THE DISPOSITION TO SECURE A TERRITORY
Those who have studied bird life throughout the year are aware that the
distribution of individuals changes with the changing seasons. During
autumn and winter, food is not so plentiful and can only be found in
certain places, and so, partly by force of circumstances and partly on
account of the gregarious instinct which then comes into functional
activity, different individuals are drawn together and form flocks of
greater or less dimensions, which come and go according to the
prevailing climatic conditions. But with the advent of spring a change
comes over the scene: flocks disperse, family parties break up, summer
migrants begin to arrive, and the hedgerows and plantations are suddenly
quickened into life. The silence of the winter is broken by an outburst
of song from the throats of many different species, and individuals
appear in their old haunts and vie with one another in advertising their
presence by the aid of whatever vocal powers they happen to possess--the
Woodpecker utters its monotonous call from the accustomed oak; the
Missel-Thrush, perched upon the topmost branches of the elm,
persistently repeats its few wild notes; and the Swallow returns to the
barn.
All of this we observe each season, and our thoughts probably travel to
the delicate piece of architecture in the undergrowth, or to the hole
excavated with such skill in the tree trunk; to the beautifully shaped
eggs; to the parent birds carrying out their work with devoted zeal--in
fact, to the whole series of events which complete the sexual life of
the individual; and the attachment of a particular bird to a particular
spot is readily accounted for in terms of one or other of the emotions
which centre round the human home.
But if this behaviour is to be understood aright; if, that is to say,
the exact position it occupies in the drama of bird life is to be
properly determined, and its biological significance estimated at its
true value, it is above all things necessary to refrain from appealing
to any one of the emotions which we are accustomed to associate with
ourselves, unless our ground for doing so is more than ordinarily
secure. I shall try to show that, in the case of many species, the male
inherits a disposition to secure a territory; or, inasmuch as the word
"secure" carries with it too much prospective meaning, a disposition to
remain in a particular place when the appropriate time arrives.
If the part which the breeding territory plays in the sexual life of
birds is the important one I believe it to be, it follows that the
necessary physiological condition must arise at an early stage in the
cycle of events which follow one another in ordered sequence and make
towards the goal of reproduction, and that the behaviour to which it
leads must be one of the earliest visible manifestations of the seasonal
development of the sexual instinct. When does this seasonal development
occur? For how long does the instinct lie dormant? In some species there
is evidence of this first step in the process of reproduction early in
February; there is reason to believe that in others the latter part of
January is the period of revival; and the possibility must not be
overlooked of still earlier awakenings, marked with little definiteness,
though nevertheless of sufficient strength to call into functional
activity the primary impulse in the sexual cycle. Here, then, we meet
with a difficulty so far as direct observation is concerned, for the
duration of the period of dormancy and the precise date of revival vary
in different species; and, if accurate information is to be obtained,
the study of the series of events which culminate in the attainment of
reproduction ought certainly to begin the moment behaviour is
influenced by the internal changes, whatever they may be, which are
responsible for the awakening of the sexual instinct.
In considering how this difficulty might be met, the importance of
migratory species as a channel of information was gradually borne in
upon me; for it seemed that the definiteness with which the initial
stage in the sexual process was marked off, as a result of the incidence
of migration, would go far towards removing much of the obscurity which
appeared to surround the earlier stages of the breeding problem in the
case of resident species. Recent observation has shown that I
exaggerated this difficulty, and that it is generally possible to
determine with reasonable accuracy the approximate date at which the
internal changes begin to exert an influence on the behaviour of
resident species also. Nevertheless, the specialised behaviour of the
migrants furnished a clue, and pointed out the direction which further
inquiry ought to take.
Those who are accustomed to notice the arrival of the migrants are aware
that the woods, thickets, and marshes do not suddenly become occupied by
large numbers of individuals, but that the process of "filling up" is a
gradual one. An individual appears here, another there; then after a
pause there is a further addition, and so on with increasing volume
until the tide reaches its maximum, then activity wanes, and the slowly
decreasing number of fresh arrivals passes unnoticed in the wealth of
new life that everywhere forces itself upon our attention. If now,
instead of surveying the migrants as a whole, our attention be directed
to one species only, this gradual arrival of single individuals in their
accustomed haunts will become even more apparent; and if the
investigation be pursued still further and these single individuals
observed more closely, it will be found that in nearly every case they
belong to the male sex. Males therefore arrive before females. This does
not mean, however, that the respective times of arrival of the males and
females belonging to any one species are definitely divided, for males
continue to arrive even after some of the females have reached their
destination; and thus a certain amount of overlapping occurs. A truer
definition of the order of migration would be as follows:--Some males
arrive before others, and some females arrive before others, but on the
average males arrive before females. This fact has long been known.
Gätke refers to it in his _Birds of Heligoland_. "Here in Heligoland,"
he says, "the forerunners of the spring migration are invariably old
males; a week or two later, solitary old females make their appearance;
and after several weeks, both sexes occur mixed, _i.e._, females and
younger males; while finally only young birds of the previous year are
met with." Newton alludes to it as follows:--"It has been ascertained by
repeated observation that in the spring movement of most species of the
northern hemisphere, the cock birds are always in the van of the
advancing army, and that they appear some days, or perhaps weeks, before
the hens"; and Dr Eagle Clarke, in his _Studies in Bird Migration_,
makes the following statement:--"Another characteristic of the spring
is that the males, the more ardent suitors, of most species, travel in
advance of the females, and arrive at their meeting quarters some days,
it is said in some cases even weeks, before their consorts." Some
interesting details were given in _British Birds_[1] in regard to the
sex of the migrants that were killed by striking the lantern at the
Tuskar Rock, Co. Wexford, on the 30th April 1914. In all, there were
twenty-four Whitethroats, nine Willow-Warblers, eight Sedge-Warblers,
and six Wheatears; and on dissection it was found that twenty
Whitethroats, seven Willow-Warblers, eight Sedge-Warblers, and one
Wheatear were males.
What a curious departure this seems from the usual custom in the animal
world! Here we have the spectacle afforded us of the males, in whom
presumably the sexual instinct has awakened, deserting the females just
at the moment when we might reasonably expect their impulse to accompany
them would be strongest; and this because of their inherited disposition
to reach the breeding grounds. If, in order to attain to reproduction,
the male depended primarily upon securing a female--whether by winning
or fighting matters not at the moment--if her possession constituted the
sole difference in his external environment between success and failure,
then surely one would suppose that an advantage must rest with those
individuals which, instead of rushing forward and inflicting upon
themselves a life of temporary isolation, remained with the females and
increased their opportunities for developing that mutual appreciation
which, by some, is held to be a necessary prelude to the completion of
the sexual act, and to which close companionship would tend to impart a
stimulus.
In thus speaking, however, we assume that the revival of the sexual
instinct in the migratory male is coincident in time with its return to
the breeding quarters; and we do so because the act of migrating is
believed to be the first step in the breeding process. But it is well to
bear in mind just how much of this assumption is based upon fact, and
how much is due to questionable inference. All that can be definitely
asserted is this, that appropriate dissection reveals in most of the
migrants, upon arrival at their destination, unquestionable evidence of
seasonal increase in the size of the sexual organs. Beyond this there is
nothing to go upon. Yet if the term "sexual instinct" is held to
comprise the whole series of complex relationships which are manifest to
us in numerous and specialised modes of behaviour, which ultimately lead
to reproduction, and which have gradually become interwoven in the
tissue of the race, there can be little doubt that the assumption is a
reasonable one. To some, the term may recall the fierce conflicts which
are characteristic of the season; to others, emotional response; to not
a few, perhaps, the actual discharge of the sexual function--all of
these, it is true, are different aspects of the one instinct; but at the
same time each one marks a stage in the process, and the different
stages follow one another in ordered sequence. However, we are not
concerned at the moment with the term in its wider application; we wish
to know the precise stage at which the disposition to mate influences
the behaviour of the male. Is the female to him, from the moment the
seasonal change in his sexual organs takes place, a goal that at all
costs must be attained? Or is it only when the cycle of events which
leads up to reproduction is nearing completion that she looms upon his
horizon? One would like to be in a position to answer these questions,
but there is nothing in the way of experimental evidence to go upon; and
if I say that there is reason to believe that, in the earlier stages,
the female is but a shadow in the external environment of the male, it
must be taken merely as an expression of opinion, though based in some
measure upon a general observation of the behaviour of various species.
Before attempting to explain the difference in the times of arrival of
the male and female migrant, let us examine the behaviour of some
resident species at a corresponding period. My investigations have been
made principally amongst the smaller species--the Finches and the
Buntings--which often pass the winter in or near the localities wherein
they brought up offspring or were reared. It is true that they wander
from one field to another according to the abundance or scarcity of
food; it is also true that, if the weather is of a type which precludes
the possibility of finding the necessary food, these wanderings may
become extensive or even develop into partial migrations. But under the
normal climatic conditions which prevail in many parts of Britain, these
smaller resident species seem to find all that they require without
travelling any great distance from their breeding haunts. Flocks
composed of Yellow Buntings, Cirl Buntings, Corn-Buntings, Chaffinches,
Greenfinches, etc., can be observed round the farmsteads or upon arable
land; small flocks of Reed-Buntings take up their abode on pieces of
waste land and remain there until the supply of food is exhausted,
deserting their feeding ground only towards evening when they retire to
the nearest reed-bed to pass the night; flocks of Hawfinches visit the
same holly-trees day after day so long as there is an abundance of
berries on the ground beneath; and so on.
I have mentioned the Reed-Bunting; let us take it as our first example
and try to follow its movements when the influence exerted by the
internal secretions begins to be reflected on the course of its
behaviour. First, it will be necessary to discover the exact localities
in any given district to which the species habitually returns for the
purpose of procreation; otherwise the earlier symptoms of any
disposition to secure a territory may quite possibly be overlooked in
the search for its breeding haunts.
In open weather Reed-Buntings pass the winter either singly, in twos or
threes, or in small flocks, on bare arable ground, upon seed fields, or
in the vicinity of water-courses; but in the breeding season they
resort to marshy ground where the _Juncus communis_ grows in abundance,
to the dense masses of the common reed (_Arundo phragmites_), and such
like places. During the winter, the male's routine of existence is of a
somewhat monotonous order, limited to the necessary search for food
during the few short hours of daylight and enforced inactivity during
the longer hours of darkness. But towards the middle of February a
distinct change manifests itself in the bird's behaviour. Observe what
then happens. When they leave the reed-bed in the morning, instead of
flying with their companions to the accustomed feeding grounds, the
males isolate themselves and scatter in different directions. The
purpose of their behaviour is not, however, to find fresh feeding
grounds, nor even to search for food as they have been wont to do, but
rather to discover stations suitable for the purpose of breeding; and,
having done so, each male behaves in a like manner--it selects some
willow, alder, or prominent reed, and, perching thereon, leads a quiet
life, singing or preening its feathers. Now if the movements of one
particular male are kept in view, it will be noticed that only part of
its time is spent in its territory. At intervals it disappears. I do not
mean that one merely loses sight of it, but that it actually deserts its
territory. As if seized with a sudden impulse it rises into the air and
flies away, often for a considerable distance and often in the same
direction, and is absent for a period which may vary in length from a
few minutes to an hour or even more. But these periodical desertions
become progressively less and less frequent in occurrence until the
whole of its life is spent in the few acres in which it has established
itself.
The behaviour of the Yellow Bunting is similar. In any roadside hedge
two or more males can generally be found within a short distance of one
another, and in such a place their movements can be closely and
conveniently followed. Under normal conditions the ordinary winter
routine continues until early in February; but the male then deserts the
flock, seeks a position of its own, and becomes isolated from its
companions. Now the position which it selects does not, as a rule,
embrace a very large area--a few acres perhaps at the most. But there is
always some one point which is singled out and resorted to with marked
frequency--a tree, a bush, a gate-post, a railing, anything in fact
which can form a convenient perch, and eventually it becomes a central
part of the bird's environment. Here it spends the greater part of its
time, here it utters its song persistently, and here it keeps watch upon
intruders. The process of establishment is nevertheless a gradual one.
The male does not appear in its few acres suddenly and remain there
permanently as does the migrant; at first it may not even roost in the
prospective territory. The course of procedure is somewhat as
follows:--At dawn it arrives and for a while utters its song, preens its
feathers, or searches for food; then it vanishes, rising into the air
and flying in one fixed direction as far as the eye can follow, until it
becomes a speck upon the horizon and is ultimately lost to view. During
these excursions it rejoins the small composite flocks which still
frequent the fields and farm buildings. For a time the hedgerow is
deserted and the bird remains with its companions. But one does not have
to wait long for the return; it reappears as suddenly as it vanished,
flying straight back to the few acres which constitute its territory,
back even to the same gate-post or railing, where it again sings. This
simple routine may be repeated quite a number of times during the first
two hours or so of daylight, with, of course, a certain amount of
variation; on one occasion the bird may be away for a few minutes only,
on another for perhaps half an hour, whilst sometimes it will fly for a
few hundred yards, hesitate, and then return--all of which shows clearly
enough that these few acres possess some peculiar significance and are
capable of exercising a powerful influence upon the course of its
behaviour. And so the disposition in relation to the territory becomes
dominant in the life of the bird.
Or take the case of the Chaffinch. In winter large or small flocks can
be found in many varied situations. But in the latter part of February,
or the early days of March, these flocks begin to disperse. At daylight
males can then be observed in all kinds of situations, either calling
loudly, uttering their spring note, or exercising their vocal powers to
the full; and it will be found that, in the majority of instances, these
males are solitary individuals, that they pass the early hours of the
morning alone, and that their normal routine of calling, singing, or
searching for food, is only interrupted by quarrels with their
neighbours. The same locality is visited regularly--not only the same
acre or so of ground, but even the same elm or oak, has, as its daily
occupant, the same cock Chaffinch. And temporary desertions from the
territory occur also, much like those referred to in the life of the
Bunting, but perhaps not so frequently. One has grown so accustomed
during the dark days of winter to the sociable side of Chaffinch
behaviour--to the large flocks searching for food, to the endless stream
of individuals returning in the evening to roost in the holly-trees, to
the absence of song--that this radical departure from the normal routine
comes as something of a surprise; for the days are still short, the
temperature is still low, the nesting season is still many weeks ahead,
and yet for part of the day, and for just that part when the promptings
of hunger must be strongest, the male, instead of joining the flock,
isolates itself and expends a good deal of energy in insuring that its
isolation shall be complete. And in place of the silence we hear from
all directions the cheerful song uttered with such marked persistency
that it almost seems as if the bird itself must be aware that by doing
so it was advertising the fact of its occupation of a territory. This is
surely a remarkable change, and the females in the meantime continue
their winter routine.
One other example. The monotonous call of the Greenfinch is probably
familiar to all. In winter these birds accompany other Finches and form
with them flocks of varying sizes, but in the spring the flocks
disperse, and the Greenfinch, in common with other units of the flock,
alters its mode of life. But whereas the Chaffinch or the Bunting begins
to acquire its territory in February, the Greenfinch only does so in
April. When the organic changes do at length begin to make themselves
felt, the male seeks a position of its own, and having found one remains
there, uttering its characteristic call. But owing probably to the fact
that it is much later than the aforementioned species in acquiring a
territory, temporary desertions are not so much in evidence. The species
is so very plentiful, and the bird is so prone to nest in gardens and
shrubberies surrounding human habitations, that this seasonal change in
its routine of existence cannot fail to be noticed. One can hear its
call in every direction, one can watch the same individual in the same
tree; and it is the male that is thus seen and heard, the female appears
later. Thus the behaviour falls into line with that of the Bunting or
the Chaffinch.
The behaviour of these resident species throws some light upon the early
arrival of the males which we are endeavouring to explain in the case of
the migrants. Let us see how their actions compare. The male resident
deserts the female early in the year and establishes itself in a
definite position, where it advertises its presence by song; the male
migrant travels from a great distance, arrives later, and also
establishes itself in a definite position, where it, too, advertises its
presence by song. The male resident passes only the earlier part of the
day in its territory at the commencement of the period of occupation;
the male migrant remains there continuously from the moment it arrives.
The male resident deserts its territory at intervals, even in the
morning; the male migrant betrays no inclination to do so. Thus there is
a very close correspondence between the behaviour of the two, and what
difference there is--slight after all--cannot be said to affect the main
biological end of securing territory. One is apt to think of the problem
of migration in terms of the species instead of in terms of the
individual. One pictures a vast army of birds travelling each spring
over many miles of sea and land, and finally establishing themselves in
different quarters of the globe; and so it comes about, I suppose, that
a country or some well-defined but extensive area is regarded as the
destination, the ultimate goal, of the wanderers. But the resident male
has a journey to perform, short though it may be; it, too, has a
destination to reach, neither a country nor a locality, but a place
wherein the rearing of offspring can be safely accomplished, and it,
too, arrives in that place in advance of the female.
With these facts at our disposal, we will endeavour to find an
explanation. It is unlikely that specialised behaviour would occur in
generation after generation under such widely divergent conditions,
and, moreover, expose the birds to risk of special dangers, if it were
but an hereditary peculiarity to which no meaning could be attached.
Hence the appearance of the males in their breeding haunts ahead of the
females becomes a fact of some importance, and suggests that the
extensive journey in the one case, and the short journey in the other,
may both have a similar biological end to serve.
Darwin evidently attached importance to this difference between the
males and the females in their times of arrival. In the _Descent of Man_
he referred to it as follows: "Those males which annually first migrated
in any country, or which in spring were first ready to breed, or were
the most eager, would leave the largest number of offspring; and these
would tend to inherit similar instincts and constitutions. It must be
borne in mind that it would have been impossible to change very
materially the time of sexual maturity in the females without at the
same time interfering with the period of the production of the young--a
period which must be determined by the season of the year." Newton
suggested the following explanation[2]: "It is not difficult to
imagine that, in the course of a journey prolonged through some 50° or
60° of latitude, the stronger individuals should outstrip the weaker by
a very perceptible distance, and it can hardly be doubted that in most
species the males are stouter, as they are bigger than the females."
Granting that the males are the stronger, how can this account for
their outstripping the females by a week, ten days, or even a fortnight,
in a journey of perhaps 1500 miles? To expect the birds to accomplish
such a distance in seven days is surely not estimating their
capabilities too highly, and any slight inequality in the power of
flight or endurance could give the males an advantage of a few hours
only. But this explanation, based upon inequalities in the power of
flight and endurance on the one hand, and the magnitude of the distance
traversed on the other, cannot afford a solution of the behaviour of the
resident males, and is less likely, therefore, to be a true solution of
that of the migrants.
There is another theory, simple enough in its way, which will probably
occur to many. It is based on the assumption that the males reach sexual
maturity before the females; and it is contended that the functioning of
the instincts which contribute towards the biological end of
reproduction depend upon the organic changes which the term "sexual
maturity" is held to embrace, and that, inasmuch as the migratory
instinct belongs to the group of such instincts, the males must be the
first to leave their winter quarters.
What is meant by the "migratory instinct"? To speak of it as one of the
instincts concerned in reproduction is not enough. Reproduction involves
the actual discharge of the sexual function, which involves the
females; but the first visible manifestation of organic change in the
male is its desertion of the females. Yet this is the behaviour which is
referred to as the "migratory instinct," and which comes into play,
according to this theory, because the bird has reached sexual maturity.
Manifestly we must have some clear understanding as to what these terms
represent. That organic changes determine the functioning of certain
definite instincts at certain specified times there can be no doubt;
that these changes may occur at a somewhat earlier date in the male than
in the female is more than probable, but that this explains the
behaviour in question I do not believe. One wants to know why the
changes should occur earlier in the male, what disposition it is which
first comes into functional activity, and to what such disposition is
related.
It may, however, be urged that, after all, this apparent eagerness to
reach the breeding grounds is but a modification of hereditary procedure
under the guiding hand of experience. What more likely result would
follow from the enjoyment associated with previous success in the
attainment of reproduction than a craving to repeat the experience? What
stronger incentive to a hurried return could be imagined? It must be
admitted that there are certain facts which might be used in support of
an appeal to experience as a reasonable explanation. For example, the
first males to arrive often display that richness of colouring which is
generally supposed to indicate a fuller maturity. Gätke even speaks of
the "most handsome old birds being invariably the first to hasten back
to their old homes." But if experience is a factor, if some dim
recollection of the past is held to explain the hurried departure of the
male migrant, one wants to know with what such recollection is
associated. Is it associated with the former female, or with the former
breeding place, or with both? I take it that any recollection, no matter
how vague, must be primarily associated with the particular place
wherein reproduction had previously been accomplished; and I grant that
if the first individuals to appear were invariably the older and
experienced birds, their early return might be explained on the basis of
such an association. But if there is reason to believe that a proportion
are young birds on the verge of carrying out their instinctive routine
for the first time, then we cannot appeal to past experience in
explanation of their behaviour.
The age of a bird is difficult to determine. Experience leads me to
believe that some of the males that arrive before the females are birds
born the previous season; one finds, for instance, individuals with
plumage of a duller hue, which denotes immaturity, amongst the first
batch of arrivals. But though plumage may sometimes be a satisfactory
guide, yet to rely upon it alone, or upon a more perfect development of
feather, is to exceed the limits of safety. How, then, can we ascertain
whether all the males that arrive before the females have had some
previous experience of reproduction? Well, we take a particular locality
and note the migrants that visit it year after year, and we find that
the respective numbers of the different species are subject to wide
annual fluctuations. Not every species lends itself to an inquiry of
this kind: some are always plentiful and fluctuation is consequently
difficult to discern; others are scarce and variation is easily
determined. Those which are of local distribution but conspicuous by
their plumage, or easily traced by the beauty or the peculiarity of
their song, afford the more suitable subjects for investigation. For
example, the Grasshopper-Warbler, Marsh-Warbler, Nightingale, Corncrake,
Red-backed Shrike, or Whinchat have each some distinctive peculiarity
which makes them conspicuous, and each one is subject to marked
fluctuation in numbers. The small plantation or wooded bank may hold a
Nightingale one year, but we miss its song there the next; the osier bed
or gorse-covered common which vibrates with the trill of the
Grasshopper-Warbler one April is deserted the following season; the
plantation which is occupied by a host of common migrants this summer
may be enlivened next year by the song of the rarer Marsh-Warbler also;
and so on. The fluctuation is considerable: we observe desertion on the
one hand, appropriation on the other, and yet males appear before
females whether the particular plantation, osier bed, or swamp had been
inhabited or not the previous season. This fact is not without
significance. It shows that similar conditions prevail both amongst the
males that appropriate breeding grounds new to them, and amongst those
that return to some well-established haunt; and on the assumption that
the earlier arrivals are experienced males, the same birds evidently do
not return to the same place year after year. Granting, then, that the
males which appropriate new breeding-grounds are young birds, how can
their earlier arrival be explained in terms of past experience; and
granting that they are old, and therefore experienced, how can it be
explained in terms of association?
Again, it may be urged that if there is some biological end to be
furthered by this hurried return, and if recollection of past experience
is a means towards that end, such recollection need not necessarily be
associated with a definite place, but only in a vague way with the whole
series of events leading up to reproduction--in which series the
migratory journey may even have acquired meaning. Whether there be any
recollection of a previous journey or of a nest with young, I do not
know. But the young bird is capable of performing its journey, of
building its nest, and of rearing its young antecedent to
experience--racial preparation has fitted it thus far; why then exclude
the other event in the series, the earlier departure of the male, from
hereditary equipment? If the journey were a casual affair without any
goal attaching to it, if the males upon arrival wandered about in search
of a mate, there would be some ground for thinking that a vague
recollection of the whole former experience was sufficient to explain
the hurried return; but since the pleasurable effect of association,
founded upon previous experience of a definite place, cannot well be
established, and since it is so difficult to study the objective aspect
of the behaviour in question without coming to the conclusion that the
journey is related to the appropriation of a place suitable for the
rearing of offspring, one is tempted to ask whether the hurried return
may not also be so related.
Now the males of some of the migratory species, especially of those
which are accustomed to return to their breeding haunts early in the
season, are called upon to face greater dangers and have a greater
strain imposed upon their strength by starting forth upon their journey
ten days or a fortnight before their prospective mates. The blizzards
which so often sweep across the northern parts of Europe in the latter
half of March, destroying in their course the all too scanty supply of
insect life, may take toll of their numbers; or the westerly gales,
which are not infrequent at that period, may meet them in mid-ocean and
add to the perils of their journey; or the temperature of the previous
weeks may have been sufficiently low to arrest the development of insect
life--and yet males are annually exposed to these risks in hurrying to
their breeding grounds. For what purpose? The answer will largely depend
upon the way in which we regard those few acres wherein a resting place
is ultimately found. For myself, I believe that they are of importance,
inasmuch as the securing of a place suitable for the rearing of
offspring is a primary condition of success in the attainment of
reproduction; and if this be so, it is evident that the interests of
the race will be better served by the males making good this first step
before the females are ready to pair, otherwise they might oscillate
between two modes of behaviour, created by the premature functioning of
conflicting impulses.
The different steps in the process seem to follow one another in ordered
sequence. The male inherits a disposition--which for us, of course, has
prospective meaning--to seek the appropriate breeding ground and there
to establish itself; and as early a functioning of this disposition as
possible, consonant with the conditions of existence in the external
environment, may have been evolved for the following reasons--firstly,
the earlier individuals will meet with less interference wherever they
may settle, every locality will be open to them, every acre free, their
only need being that particular environment for which racial preparation
has fitted them. In the second place, being already established when
other males appear upon the scene, and advertising their presence by
song, they will be less liable to molestation; thirdly, in those cases
in which a long journey is undertaken, they will have ample time to
recover from the fatigue, and, if attacked by later arrivals, will thus
be in a better position to defend their territories; and lastly, a
greater uniformity in their distribution will be insured before the
females begin their search.
There is, besides, another good reason for thinking that the earlier
males will have an advantage. We will assume--and from the abundant
evidence supplied by the marking of birds, it is quite a reasonable
assumption--that there is a tendency, generally speaking, for
individuals to return to the neighbourhood of their birthplace, or to
the place in which they had previously reared their offspring. Now the
earlier arrivals will have no difficulty in securing territories; those
that come later may have to search more diligently, still they will gain
all that they require so long as any available space remains. Then comes
the point when all suitable ground is occupied, and yet there are males
to be provided for. What will be the position of these males? Urged by
their inherited nature, they will leave the district and possibly
continue their search into those adjoining, only, however, to add to the
difficulties of the males there similarly situated; and even allowing
that they are at length successful in establishing themselves, what are
their prospects of securing mates? Since the earlier females will not
extend their wanderings farther than is absolutely necessary, but will
pair whenever the opportunity for doing so arises, it is to the later
females, forced onwards by competition, that the late males must look
for mates; so that when at length pairing does take place, much valuable
time will have been lost.
The disadvantages which the late arrivals have to face are therefore
great, and it is probable that the percentage which attain to
reproduction will on the average be somewhat lower than the percentage
in the case of the earlier arrivals. The district in which my
observations have been made lies well within the limits of the breeding
range of most of our common species, and it is not surprising that I
should have met with little evidence of failure to breed as a result of
failure to secure territory. Some interesting information was supplied
to me, however, by the late Robert Service. He found, in certain seasons
in Dumfriesshire, flocks of from ten to fifty unmated Sedge-Warblers,
which, from the time of their arrival in May until the middle of July,
haunted reed-filled spaces along stagnant streams. These flocks appeared
to him to be composed of loosely-attached individuals of a migrant flock
that had failed to find things congenial enough to entice them to
disperse. But may they not have been composed of males that had failed
to secure territories, or of females that had failed to discover males
in possession of territories, or of both?
We have seen that, in the case of many species, each male establishes
itself in a particular place at the commencement of the breeding season,
even though this may mean a partial or perhaps a complete severance from
former companions. We must now discuss this fact in greater detail
because it is opposed to the views often held regarding the sexual
behaviour of birds, and is manifestly of importance when considering
the theory of breeding territory.
First, however, there is a point which requires some explanation. I
speak of the _same_ male being in the _same_ place. How can I prove its
identity? In the first place it is highly improbable that a bird which
roams about within the same small area of ground, makes regular use of a
certain tree and a certain branch of that tree, and observes a similar
routine day after day, can be other than the same individual. But, apart
from this general consideration, are there any means by which
individuals of the same species can be identified? Well, there is
variation in the plumage. Supposing we take a dozen cock Chaffinches and
examine them carefully, we shall find slight differences in pattern and
in colour--more grey here or a duller red there, as the case may be--and
though these differences may not be sufficient to enable us to pick out
a bird at a distance, they are nevertheless conspicuous when it is close
at hand. Then again there is variation in the song; and the more highly
developed the vocal powers the greater scope there is for variation. But
even the phrases of a simple song can be split up and recombined in
different ways. If one were asked casually whether the different phrases
of the Reed-Bunting's song always followed one another in the same
sequence, the answer would probably be that they certainly did so,
whereas the bird is capable of combining the few notes it possesses in a
surprising number of different ways. And lastly, there are differences
in just the particular way in which specific behaviour, founded upon a
congenital basis, is adapted by each individual to its own special
environment. Racial preparation determines behaviour as a whole, but the
individual is allowed some latitude in the execution of details which
are in themselves of small moment--the selection of a particular tree as
a headquarters and a particular branch upon that tree, the direction of
the distant excursion, and the direction of the limited wanderings
within the small area surrounding the headquarters which in the course
of time determine the extent of the territory, are matters for each
individual to decide when the occasion for doing so arises. Moreover
instances of abnormal coloration or abnormal song are not rare, and they
are valuable since they place the identity of the individual beyond
dispute. I can recall the case of a Willow-Warbler whose song was unlike
that of its own or any other species, and of a Redbreast whose voice
puzzled me not a little. I can recollect also a male Yellow Bunting
whose foot was injured or deformed. Of this bird's behaviour I kept a
record for two months or so; and inasmuch as it inhabited a roadside
hedge, and was of fearless disposition, the deformed foot could plainly
be seen whenever it settled upon the road to search for food.
Identification is not, therefore, a difficulty. There is always some
small difference in colour or in song, or some well-defined routine
which makes recognition possible.
Owing to their great powers of locomotion, birds have generally been
regarded as wanderers more or less; anything in the nature of a fixed
abode, apart from the actual nest, having been accounted foreign to
their mode of life; and even the locality immediately surrounding the
nest has not been apprehended as possessing any meaning for the owner of
that nest. No doubt the supply of food determines their movements for a
considerable part of the year; they seek it where they can find it, here
to-day, there to-morrow--in fact few species fail to move their quarters
at one season or another, so that there is much truth in the notion that
birds are wanderers. Yet to suppose that every individual one sees or
hears--every Lapwing on the meadow, or Nightingale in the withy bed--is
in that particular spot just because it happens to alight there as it
roams from place to place, is to take a view which the observed facts do
not support. For as soon as the question of reproduction dominates the
situation, a new condition arises, and the habits formed during the
previous months are reversed, and the males, avoiding one another, or
even becoming actively hostile, prefer a life of seclusion to their
former gregariousness--all of which occurs just at the moment when we
might reasonably expect them to exhibit an increased liveliness and
restlessness as a result of their endeavour to secure mates; and so
universal is the change that it might almost be described as an
accompaniment of the sexual life of birds generally.
That the Raven and certain birds of prey exert an influence over the
particular area which they inhabit has long been known, and it has been
recognised more especially in the case of the Peregrine Falcon,
possibly because the bird lives in a wild and attractive country, and,
forcing itself under the notice of naturalists, has thus had a larger
share of attention devoted to its habits. Moreover, when a species is
represented by comparatively few individuals, and each pair occupies a
comparatively large tract of country, it is a simple matter to trace the
movements and analyse the behaviour of the birds. There is a rocky
headland in the north-west of Co. Donegal comprising some seven miles or
so of cliffs, where three pairs of Falcons and two pairs of Ravens have
nested for many years. Each year the different pairs have been more or
less successful in rearing their young; each year the young can be seen
accompanying their parents up to the time when the sexual instinct
arises; and yet the actual number of pairs is on the whole remarkably
constant, and there is no perceptible increase. It seems as if the
numbers of three and two respectively were the maximum the headland
could maintain. But this is no exceptional case; it represents fairly
the conditions which obtain as a rule amongst those species, granting,
of course, a certain amount of variation in the size of each territory
determined by the exigencies of diverse circumstances.
If we take a given district, and devote our attention to the smaller
migrants that visit Western Europe each returning spring for the purpose
of procreation, we shall find that the movements of the males are
subject to a very definite routine. This, however, is not true of every
male; some may be wending their way to breeding grounds at a distance;
others may be seeking the particular environment to which they may be
adapted; others again, having found their old haunts destroyed, may
consequently be seeking new.
Of all this there is evidence. Small parties of Chiffchaffs pass through
a district on their way to other breeding grounds, flitting from hedge
to hedge as they move in a definite direction with apparently a definite
purpose; Reed-Warblers settle in a garden or plantation, eminently
unsuited to their requirements, and disappear; Wood-Warblers arrive in
some old haunt, and finding it no longer suitable for their purpose,
seek new ground. So that plenty of individuals are always to be found,
which, for the time being at least, are wanderers.
In the district which I have in mind, the wandering males form only a
small part of the incoming bird population. The majority of individuals
that fall under observation are those that have made this particular
district their destination; and in doing so, they may possibly have been
guided by their experience as owners or inmates of former nests, for it
cannot be doubted that a return to the neighbourhood of the birthplace
would lead to a more uniform distribution and therefore be advantageous,
and the tendency to do so might consequently have become interwoven in
the tissue of the race. How, then, do they behave? A certain amount of
movement, an interchanging of positions, even though restricted to an
area defined, let us say, by experience, might be expected under the
circumstances--that, however, is not what we find; we observe the
available situations plotted out into so many territories, each one of
which is occupied by a male who passes the whole of his time therein.
Take whatever species we will--Whitethroat, Whinchat, Willow-Warbler,
Red-backed Shrike, it matters not which, for there is no essential
difference in the general course of procedure--this condition will be
found to prevail. Generally speaking, the behaviour in relation to the
territory can be studied more conveniently where a number of individuals
of the same species have established themselves in proximity to one
another. Such species as the Chiffchaff, Willow-Warbler, or Wood-Warbler
are often sufficiently common to allow of three or more of their
respective males being kept in view at the same time; and the
disposition to occupy a definite position can be readily observed. The
Reed-Warbler is a suitable subject for an investigation of this kind;
for since it is restricted by its habits to localities wherein the
common reed (_Arundo phragmites_) grows in abundance, and since such
localities are none too plentiful and often limited in extent, the area
occupied by each individual is necessarily small--if it were not so the
species would become extinct. Hence it is a simple matter to study the
routine of the different individuals and to mark the extent of their
wanderings.
In this way the males of all the Warblers that breed commonly in Great
Britain establish themselves, each one in its respective station at the
respective breeding ground; so, too, do those of many other
migrants--for example, the Whinchat, Wheatear, Tree-Pipit, and Red-backed
Shrike. All of these, it is true, are common species--numbers of
individuals can often be found in close proximity--and therefore it may
be argued that they keep to one position more from pressure of
population than from any inherited disposition working towards that end.
But the rarer species behave similarly. Districts frequented by the
Marsh-Warbler and offering plenty of situations of the type required by
the bird are often inhabited by a few members only, and yet the
disposition to remain in a definite position is just as marked.
You will say, however, that these smaller migrants have no exceptional
powers of flight; that they have besides just completed a long and
arduous journey; and you will ask why they should be expected to wander,
whether it is not more reasonable to expect that, in order to overcome
their fatigue, they should remain where they settle. The Cuckoo is a
wanderer in the wider sense of the term, and is gifted with considerable
powers of flight. Upon arrival the male flies briskly from field to
field, showing but little signs of weariness; yet we have only to follow
its movements for a few days in succession to assure ourselves that the
bird is no longer a wanderer; for just as the Warbler or the Chat moves
only within a definitely delimited area, so the male Cuckoo, strange as
it may seem, restricts itself to a particular tract of land. The area
over which it wanders is often considerable and consequently it is not
possible to keep the bird always in view, but inasmuch as the variation
in the voices of different individuals is quite appreciable,
identification is really a simple matter. If we cannot keep the bird in
sight, we can trace its movements by sound and mark the extent of its
wanderings, which by repetition become more and more defined, until a
belt of trees here, or an orchard there, mark a rough and rarely passed
boundary line.
Let us take another example from the larger migrants--the Black-tailed
Godwit, a bird common enough in the Dutch marshes but no longer breeding
in this country. On suitable stretches of marsh land, numbers will be
found in proximity one to another after the manner of the Lapwing, each
male occupying a definite space of ground wherein it passes the time
preening, searching for food, or in sleep--though at the same time
keeping a strict watch over its territory. Now the preference shown for
a particular piece of ground, and the determination with which it is
resorted to, is the more remarkable when we take into consideration the
specific emotional behaviour arising from the seasonal sexual condition.
This behaviour is expressed in a peculiar flight. The bird rises high in
the air, circles round with slowly beating wings above the marsh, and
utters a call which, as far as my experience goes, is characteristic of
the performance. The air is often full of individuals circling thus
even beyond the confines of the marsh, for a male does not limit its
flight to a space immediately above its territory; but nevertheless
careful observation will show how unerringly each one returns to its own
position on the breeding ground, no matter how extensive the aerial
excursion may have been. And so, when the males of the smaller migrants
confine their movements to an acre of ground at the completion of their
long journey, they are acting no more under the influence of fatigue
than the Cuckoo, which keeps within certain bounds yet flies about
briskly, or the Godwit which, though holding to its few square yards on
the ground, executes most tiring and extensive flights above the marsh.
Of all the migrants, however, the behaviour of the Ruff is perhaps the
most strange, and though it has long been known that these birds have
their special meeting places where they perform antics and engage in
serious strife, yet it is only within recent years that the primary
purpose of these gatherings has been ascertained--that purpose being the
actual discharge of the sexual function. Mr. Edmund Selous has carried
out some exhaustive investigations into their activities at the meeting
places, and he makes it clear that each bird has its allotted position.
He says, for example, that "It begins to look as though different birds
had little seraglios of their own in different parts of the ground,"
that "each Ruff has certainly a place of its own," or again that "this
Ruff indeed, which I think must be a tender-foot, does not seem to have
a place of its own like the others." Nevertheless it is only at the
meeting places that they have their special positions; there is no
evidence to show that each one has a special territory, wherein it seeks
its food, as the Warbler has, and therefore some may think that we are
here confronted with behaviour of a different order. But we must bear in
mind that the process has been adjusted to meet the requirements of
different species: the size of the territory, the period of its daily
occupation, the purpose which it serves--these all depend upon manifold
relationships and do not affect the principle. Why it has been
differentiated in different circumstances we shall have occasion to
discuss later; for the moment it is enough that at the end of its
migratory journey each Ruff occupies one position on the meeting ground.
[Illustration: Territorial flight of the Black-tailed Godwit
Emery Walker ph.sc.]
Now birds that are paired for life, whose food-supply is not affected by
alternations of climate, have no occasion to desert the locality wherein
they have reared their offspring, and so their movements, being subject
to a routine which would tend to become increasingly definite, must in
the course of time and according to the law of habit formation become
organised into the behaviour we observe. Is it necessary, therefore, to
seek an explanation of their tendency to remain in one place in anything
so complex as an inherited disposition? Again, since we have to confess
to so very much ignorance on so many points connected with the whole
phenomenon of migration, may there not be some condition, hitherto
shrouded in mystery, which might place so different a complexion on the
corresponding aspect of migrant behaviour as to rid us, in their case
also, of the necessity of appealing to an inherited disposition? Such
questions are justifiable. And if the life-histories of other species
gave no further support to our interpretation, if, in short, the
evidence were to break down at this point, then we should be forced to
seek some other explanation more in keeping with the general body of
facts.
But far from placing any obstacle in the way of an interpretation in
terms of inherited disposition, the behaviour of many of those residents
which are not paired for life gives us even surer ground for that
belief. Moreover in their case the initial stages in the process are
more accessible to observation. I will endeavour to explain why. In the
process of reproduction the environment has its part to play--whether in
the manner here suggested, or indirectly through the question of
food-supply, matters not at the moment. Now, migratory species are more
highly specialised than resident species as regards food, and are
affected more by variations of temperature, so that they can live for
only a part of the year in the countries which they visit for the
purpose of procreation. Hence the organic changes, which set the whole
process in motion, must be coincident in time with the growth of
appropriate conditions in the environment; for if it were not so, if the
internal organic changes were to develop prematurely, the bird would
undertake its journey only to find an insufficiency of food upon its
arrival, and this would scarcely contribute towards survival. Definite
limitations have therefore been imposed upon the period of organic
change. But in the case of many resident species the conditions are
somewhat different, for they remain in the same locality throughout the
year, and a gradual unfolding of the reproductive process cannot
therefore have a similarly harmful effect. Thus it comes about that the
behaviour of the migrant, when it arrives at the breeding ground and
first falls under observation, represents a stage in the process which,
in the case of the resident, is only reached by slow degrees; and by
closely observing the behaviour as it is presented to us in the life of
the resident male, we not only gain a better insight into the changes in
operation, but can actually witness the breaking down of the winter
routine, stereotyped through repetition, by the new disposition as it
arises.
The first visible manifestations, even though they may be characterised
by a certain amount of vagueness, are therefore of great importance if
the behaviour is to be interpreted aright; and in order to insure that
none of these earlier symptoms shall be missed, it is necessary to begin
the daily record of the bird's movements at an early date in the season.
As a rule the second week in February is sufficiently early for the
purpose, but the date varies according to the prevailing climatic
conditions. Even in species widely remote there is great similarity of
procedure, and the behaviour of the Buntings is typical of that of many.
With the rise of the appropriate organic state the male resorts at
daybreak to a suitable environment, occupies a definite position, and
singling out some tree or prominent bush, which will serve as a
headquarters, advertises its presence there by song. At first the bird
restricts its visits, which though frequent in occurrence are of short
duration, for the most part to the early hours of the morning; it
disappears as suddenly as it appeared, and one can trace its flight to
the feeding grounds--a homestead or perhaps some newly sown field. But
by degrees the impulse to seek the society of the flock grows less and
less pronounced, the visits to the territory are more and more
prolonged, and the occupation of it then becomes the outstanding feature
of the bird's existence. This in outline is the course of procedure as
it appears to an external observer.
But although much can be learnt from the lives of these smaller species,
there is no gain-saying the fact that a great deal of patient
observation is required, and the process is apt to become tedious. There
are others, however, which are more readily observed, whilst their
life-histories afford just as clear an insight into the effect produced
by the new disposition upon the developing situation; and among these
the Lapwing takes a prominent position, because it is plentiful and
inhabits open ground where it is easily kept in view.
There is a water meadow with which I am familiar, where large numbers
resort annually for the purpose of procreation. Here they begin to
arrive towards the end of February, and at first collect in a small
flock at one end of the meadow. A male, here and there, can then be seen
to break away from the flock, and to establish itself in a definite
position upon the unoccupied portion of the ground, where it remains
isolated from its companions. Others do likewise until the greater part
of the meadow is divided into territories. Six of these territories I
kept under observation for approximately two months in the year 1915.
The occupant of the one marked No. 6 upon the 1915 plan was a lame bird,
a fortunate occurrence as it enabled me to follow its movements with
some accuracy; and though it maintained its position for some weeks, it
ultimately disappeared, as a result, I believe, of the persistent
attacks of neighbouring males. The behaviour of the males during the
first fortnight or so after they broke away from the flock was
interesting. Though they retired to their territories and remained in
them for the greater part of their time, yet it was only by degrees that
they finally severed their connection with the flock, for so long as a
nucleus of a flock remained, so long were they liable to desert their
territories temporarily and to rejoin their companions.
[Illustration: Emery Walker Ltd. sc.
Plan of the water meadow showing the territories occupied by Lapwings in
the year 1915.]
[Illustration: Emery Walker Ltd. sc.
Plan of the water meadow showing the territories occupied by Lapwings in
the year 1916.
_Between pages 58 and 59._]
Lapwings, as is well known, collect in flocks during the winter months,
and these flocks, which sometimes reach vast proportions, are to be
found on tidal estuaries, water meadows, arable land, and such like
places, according to the prevailing climatic conditions. This flocking
may contribute towards survival, and may therefore be the result of
congenital dispositions which have been determined on biological
grounds. On the other hand, since food at that season is only to be
obtained in a limited number of situations, the birds may be simply
drawn together by accident. In the former case the behaviour would be
instinctive, in the latter, though accidental at first, recurrent
repetition would tend to make it habitual; but in either case the
impulse to accompany the flock must be a powerful one, for on the one
hand it would depend upon inherited, and on the other hand upon
acquired, connections in the nervous system. Now observe that soon
after the flock arrived in the meadow, single males detached themselves;
there was no hesitation, they just retired from their companions and
settled in their respective territories. They were not expelled, for if
their leaving had been compulsory much commotion would have preceded
their departure, and their return would certainly not have been
welcomed. A reference to the plan will make the position clearer; the
neutral zone inhabited by the flock is there shown as situated in one
corner of the meadow, the territories that fell under observation are
plotted out as far as possible to scale, and the more important zones of
conflict are also marked.
The males spent part of their time in their respective territories and
part with the flock, so long as it remained in existence. When a male
was in its territory it avoided companions and was openly hostile to
intruders; when it was with the flock it wandered about with companions
in search of food. The contrast between the two modes of behaviour was
very marked, and it was evident that the gregarious instinct was
gradually yielding its position of importance to the new factor--the
territory. If there had been no flock, if a few solitary individuals had
appeared here and there and had established themselves in different
parts of the meadow, one would have had no definite evidence of the
strength of the impulse in the male to seek a position of its own, one
could only have argued from the general fact of males flocking in the
winter and isolating themselves in spring that something more than
accident was required to explain so radical a change. But since the
birds returned in a flock to the ground upon which they intended to
breed, and since the flock occupied temporarily part of the ground
whilst the partitioning of the remainder was still proceeding, it was
possible to gauge the strength of the impulse, which was forcing the
males to isolate themselves in particular areas of ground, by comparing
it with the impulse to accompany the flock--and the measure of its
intensity was the rapidity with which the latter impulse yielded its
position of importance.
Like the Lapwing, the Coot and Moor-Hen are easily kept under
observation, and since many individuals often breed in proximity, more
than one can be watched at the same moment; moreover the area occupied
by each male generally embraces an open piece of water as well as part
of the fringe of reeds, so that the movements of the bird can be
followed without much difficulty. Under favourable conditions
manifestations of the developing situation become visible at a
comparatively early date in the season--the middle or the latter part of
February--and these manifestations resemble those of other species. But
the Moor-Hen passes summer and winter alike in the same situation, and
being therefore in a position to respond at once to internal
stimulation, however vague, the change from the one state to the other
is gradual. This, however, is a matter of detail; the main consideration
lies in the fact that the impulse to retire to a definite position, to
avoid companions, and to live in seclusion, is strongly marked, and
produces a type of behaviour similar on the whole to that of the
Lapwing. First of all there is the appropriation of a certain position,
the limits of which are fixed according to the law of habit formation,
and according to the pressure exerted by neighbouring individuals; then
there is the neutral ground over which the birds wander amicably in
search of food; and finally there is the contrast between the pugnacity
of the male whilst in its territory, and its comparative friendliness
when upon neutral ground.
Evidence of similar behaviour is to be found in the life of the Black
Grouse, a bird which has always excited the curiosity of naturalists on
account of the special meeting places to which both sexes resort in the
spring. Mr. Edmund Selous watched these birds in Scandinavia, where he
kept a daily record at one of the meeting places. In various passages he
refers to the appropriation of particular positions by particular males,
and concludes thus: "It would seem from this that, like the Ruffs, each
male Blackcock has its particular domain on the assembly ground, though
the size of this is in proportion to the much greater space of the
whole. On the other mornings, too, the same birds, as I now make no
doubt they are, have flown down into approximately the same areas."
The cliff-breeding species--Guillemots, Razorbills, and Puffins--are
difficult to investigate because individuals vary so little, and the
sexes resemble one another so closely; yet, despite these difficulties,
we can gain some idea of the general purport of their activities. But
when the ledges are crowded and the air is filled with countless
multitudes, how is it possible to keep a single bird in view for a
sufficient length of time to understand its routine? The difficulty is
not an insuperable one. The flights, undertaken seemingly for no
particular purpose, are often of short duration and are completed before
the strain of observation becomes too great; moreover an individual
sometimes possesses a special mark or characteristic which serves to
make it conspicuous. For example, there is a well-marked variety of the
Common Guillemot, the Ringed or Bridled Guillemot of science,
distinguished by an unusual development of white round the eye and along
the furrow behind it. One such individual I was fortunate in discovering
upon a crowded cliff, and, as in the case of the Lapwing with the broken
leg or the Yellow Bunting with the injured foot, the identity of the
bird was beyond dispute, and one could observe that it appropriated to
itself a particular position upon a particular ledge.
Guillemots and Razorbills return at intervals to the breeding stations
early in the season, and these visits are repeated with growing
frequency until the birds are finally established. I have witnessed
these periodic returns during March in the south of England, and during
April in the north-west of Ireland, and I am informed that in the latter
district such visits may occur as early as February. Gätke, who had
ample opportunity of observing the birds in Heligoland, puts their
return at an even earlier date. "They visit their breeding places," he
says, "in flocks of thousands at the New Year, often even as early as
December, as though they wanted to make sure of their former haunts
being well preserved and ready for their reception." Such visits,
however, are irregular in occurrence; the birds arrive, and, after
spending a short time upon the ledges, disappear. And since there is not
the same evidence in their coming and going of that method which we
observe in the periodical returns of the Bunting or the Finch, it may be
thought that needless importance is being attached to an episode in
their lives which is quite intelligible in terms of a feeble response
determined by a dawning organic change. While it may be quite
intelligible in such terms it is not thereby explained; for every
response must have as its antecedent an inherited connection in the
nervous system determined on biological grounds. Besides, these early
periodic returns conform in general to the type of behaviour displayed
by other species, the males of which return to their breeding grounds
many weeks before the real business of reproduction begins. Are we then
justified in regarding them as accidents of the developing situation?
Are we not rather bound to admit that they have some definite biological
end to serve?
[Illustration: Competition for territory is seldom more severe than
amongst cliff-breeding sea birds, and the efforts of individual
Razorbills to secure positions on the crowded ledges lead to desperate
struggles.
Emery Walker ph.sc.]
These examples show that the males of many species reverse their mode of
life at the commencement of the breeding season and proceed to isolate
themselves, each one in a definitely delimited area.
There are three ways in which we may attempt to interpret this
particular mode of male behaviour. We may regard it as an accidental
circumstance, nowise influencing the course of subsequent procedure; or,
appealing to the law of habit formation, we may regard it as an
individual acquirement; or again, we may invest it with a deeper
significance and seek its origin in some specific congenital disposition
determined on purely biological grounds.
Which of these three shall we choose? The first by itself requires but
little consideration; for though it might explain the initial visit, it
cannot account for the persistency with which the plot of ground is
afterwards resorted to. Supposing, however, that we combine the first
and the second; supposing, that is to say, we assume, for the purpose of
argument, that the initial visit is fortuitous, and that constancy is
supplied by habit formation--would that be a satisfactory
interpretation? It is a simple one, inasmuch as it only requires that a
male shall alight by chance in a particular place for a few mornings in
succession in order that the process may be set in motion. Now an
essential condition of habit formation is recurrent repetition; given
this repetition and, it is true, any mode of activity is liable to
become firmly established. But how can we explain the repetition? Even
if we are justified in assuming that the initial visit is purely an
accidental occurrence, we cannot presume too far upon the laws of chance
and assume that the repetition, at first, is also fortuitous.
So that we come back to the congenital basis, the last of our three
propositions. And it will, I think, be admitted that the facts give us
some grounds for believing that the securing of the territory has its
root in the inherited constitution of the bird. In comparing the
behaviour of the migratory male with that of the resident, attention was
drawn to the manner in which the occupation of a territory was effected:
the former bird, it may be remembered, established itself without delay,
whereas the latter did so only by degrees, and the difference was
attributed to the incidence of migration which required a closer
correspondence between organic process and external environment. But the
significance for us just now lies in the fact that the definiteness,
which accompanies the initial behaviour of the migratory male in
relation to the territory, cannot have been acquired by repetition; for
this reason, that when the male occupies its space of ground at the end
of its long and arduous journey, it does so without preparation or
experiment, even without hesitation, as if aware that it was making good
the first step in the process of reproduction. No doubt, if it happened
to be an individual that had already experienced the enjoyment of
reproduction, it might be aware of the immediate results to be achieved
and act accordingly. But among the hosts of migrants that one observes,
there must be many males which have not previously mated; and yet, upon
arrival, they all behave in a similarly definite manner--so that
experience cannot well be the primary factor in the situation. If, then,
the essential condition of habit formation is absent and experience is
eliminated, there is nothing left but racial preparation to fall back
upon.
Nevertheless, it is true that many resident males seem to pass through
a period of indecision before they establish themselves permanently in
their respective territories; they come and go, their visits grow more
and more prolonged, and only after the lapse of some considerable time
does the process of establishment attain that degree of completeness
which is represented in the initial behaviour of the migratory male.
Their whole procedure seems therefore to bear the stamp of individual
acquirement; and, if it stood alone, we might be content to construe it
thus, but the example of the migratory male necessitates our looking
elsewhere for the real meaning of the indecision.
Let me first of all give some instances of the persistence with which a
male remains in one spot, and this despite the fact that it has no mate.
A Reed-Bunting occupied a central territory in a strip of marshy ground
inhabited annually by four or five males of this species. Throughout
April, May, and until the 19th June, it clung to its small plot of
ground, tolerated no intrusion, and sang incessantly.
Two Whitethroats arrived at much the same time--the 30th April
approximately--and occupied the corner of a small plantation; the one
obtained a mate the day following its arrival, the other remained
unpaired for a fortnight.
A Reed-Warbler established itself amongst some willows and alders
adjoining a reed-bed and made its headquarters in a small willow bush.
Not more than fifteen yards away, on the edge of the main portion of the
reeds, another male was established and was paired on the 22nd May. Each
morning the single male behaved in much the same way, singing
continuously whilst perched upon the bush. And so the days passed by
until it seemed improbable that it would ever secure a mate, but one
appeared on the 20th June, and a nest was built forthwith.
Now it is difficult to believe that a chance visit, even though repeated
for a few mornings in succession, could have accounted for the
Reed-Bunting remaining so persistently in the marsh, or the Whitethroat
in one corner of the osier bed, or the Reed-Warbler in that one
particular willow. Not only so, but if a habit of such evident strength
can be acquired so readily, we have a right to ask why it should only be
acquired in the spring--why not at every season? Considerations such as
these lead to the belief that there must be some congenital basis to
account for such persistent endeavour; the more so since it is difficult
not to be impressed with the conative aspect of the male's behaviour. To
a stranger, unacquainted with its previous history, the bird might
appear to be leading a life of hesitation, whereas, if carefully
watched, its whole attitude will be found to betray symptoms of a
striving towards some end; and the frequent departure and return, which
might be pointed to as the material from which a definite mode of
procedure would be likely to emerge, is in reality behaviour of a
determinate sort.
My interpretation, then, of the apparent indecision in the behaviour of
the resident male is this. During the winter most species live in
societies, together they seek their food and together they retire in the
evening to the accustomed roosting places; and the association of
different individuals confers mutual benefits upon the associates. The
movements of these societies are dominated by the question of food; all
else is subservient, and the supply of the necessary sustenance may,
under certain conditions, become a difficulty which can only be met by
energy and resource. After the long night the sensation of hunger is
strong, and the birds, on awakening, fly to the accustomed feeding
grounds, returning again in the evening to the selected spot, and by
frequent repetition a routine becomes established. Thus the behaviour of
each individual is determined not only by the powerful gregarious
impulse but also by the habits formed in connection therewith during
many weeks in succession. Now with the rise of the appropriate organic
state, the disposition to seek the breeding ground and there to
establish itself becomes dominant in the male. But the process is a
gradual one. There is no need, as happens amongst the migrants, for the
period of organic change to conform rigidly to the growth of any
particular condition in the environment, and hence for a time the bird
oscillates between two modes of behaviour--between that one organised by
frequent repetition and that one determined by the functioning of this
new disposition.
To look at the matter broadly, it is scarcely likely that so definite a
mode of behaviour would recur with such regularity, generation after
generation, in the individuals belonging to so many widely divergent
forms, if it had no root in the inborn constitution of the bird. But the
law of habit formation has its part to play also. By itself it is
inadequate; yet it probably does assist very materially in adding still
greater definition, and it probably is responsible in a large measure
for determining the limits of the territory according to the conditions
of existence of the species--thus the Falcon seeks its prey over wide
tracts of land, and, by hunting over certain ground repeatedly,
establishes a routine, which broadly fixes the area occupied; the
Woodpecker cannot find food upon every tree, and every forest does not
contain the necessary trees, and therefore the bird regulates its flight
according to the position of the trees; and the Warbler, finding food
close at hand, does not need to travel far, and the area it occupies is
consequently small.
So that the most likely solution of the problem will be found in a
combination of our second and third propositions; that is to say, in an
initial responsive behaviour provided for in the inherited constitution
of the nervous system, and in a definiteness acquired by repetition and
determined by relationships in the external environment.