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| TRANSCRIBER'S NOTE: |
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| There are a large number of compound words in |
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TERRITORY IN BIRD LIFE
[Illustration: A pair of Lesser Spotted Woodpeckers attacking a Great
Spotted Woodpecker
Emery Walker ph.sc.]
TERRITORY IN
BIRD LIFE
BY H. ELIOT HOWARD
WITH ILLUSTRATIONS BY
G. E. LODGE AND H. GRÖNVOLD
NEW YORK
E. P. DUTTON AND COMPANY
1920
PREFACE
When studying the Warblers some twenty years ago, I became aware of the
fact that each male isolates itself at the commencement of the breeding
season and exercises dominion over a restricted area of ground. Further
investigation, pursued with a view to ascertaining the relation of this
particular mode of behaviour to the system of reproduction, led to my
studying various species, not only those of close affinity, but those
widely remote in the tree of avian life. The present work is the outcome
of those investigations. In it I have endeavoured to interpret the
prospective value of the behaviour, and to trace out the relationships
in the organic and inorganic world which have determined its survival.
Much is mere speculation; much with fuller knowledge may be found to be
wrong. But I venture to hope that a nucleus will remain upon which a
more complete territorial system may one day be established.
I have to thank Mr. G. E. Lodge and Mr. H. Grönvold for the trouble they
have taken in executing my wishes; I also want to record my indebtedness
to the late E. W. Hopewell; and to Professor Lloyd Morgan, F.R.S., I am
beholden more than I can tell.
CONTENTS
PAGE
CHAPTER I
INTRODUCTION 1
CHAPTER II
THE DISPOSITION TO SECURE A TERRITORY 20
CHAPTER III
THE DISPOSITION TO DEFEND THE TERRITORY 73
CHAPTER IV
THE RELATION OF SONG TO THE TERRITORY 119
CHAPTER V
THE RELATION OF THE TERRITORY TO THE SYSTEM
OF REPRODUCTION 169
CHAPTER VI
THE WARFARE BETWEEN DIFFERENT SPECIES AND ITS
RELATION TO THE TERRITORY 216
CHAPTER VII
THE RELATION OF THE TERRITORY TO MIGRATION 259
INDEX 302
LIST OF ILLUSTRATIONS
_Face page_
A pair of Lesser Spotted Woodpeckers attacking a Great
Spotted Woodpecker _Frontispiece_
Territorial flight of the Black-tailed Godwit 54
Competition for territory is seldom more severe than
among cliff-breeding seabirds, and the efforts of
individual Razorbills to secure positions on the
crowded ledges lead to desperate struggles 64
Male Blackbirds fighting for the possession of territory.
The bare skin on the crown of the defeated bird shows
the nature of the injuries from which it succumbed 74
Male Cuckoos fighting before the arrival of a female 82
Two pairs of Pied Wagtails fighting in defence of their
territories 86
Long-tailed Tit: males fighting for the possession of
territory. The feathers have been torn from the crown
of the defeated and dying rival 96
A battle between two pairs of Jays 106
The Female Chaffinch shares in the defence of the territory
and attacks other females 110
Peregrine Falcon attacking a Raven 216
A battle between a pair of Green Woodpeckers and a
Great Spotted Woodpecker for the possession of a hole
in an oak-tree 238
Plans of the Water-meadow showing the Territories
occupied by Lapwings in 1915 and 1916 _Between_ 58 and 59
SCIENTIFIC NAMES OF BIRDS MENTIONED IN THE TEXT
Raven _Corvus corax._
Carrion-Crow _Corvus corone._
Hooded Crow _Corvus cornix._
Rook _Corvus frugilegus._
Magpie _Pica pica._
Jay _Garrulus glandarius rufitergum._
Chough _Pyrrhocorax pyrrhocorax._
Starling _Sturnus vulgaris._
Greenfinch _Chloris chloris._
Hawfinch _Coccothraustes coccothraustes._
House-Sparrow _Passer domesticus._
Chaffinch _Fringilla coelebs._
Brambling _Fringilla montifringilla._
Linnet _Acanthis cannabina._
Corn-Bunting _Emberiza calandra._
Yellow Bunting _Emberiza citrinella._
Cirl Bunting _Emberiza cirlus._
Reed-Bunting _Emberiza schoeniclus._
Sky-Lark _Alauda arvensis._
Pied Wagtail _Motacilla lugubris._
Tree-Pipit _Anthus trivialis._
Meadow-Pipit _Anthus pratensis._
Great Titmouse _Parus major newtoni._
Blue Titmouse _Parus coeruleus obscurus._
Long-tailed Titmouse _Ægithalus caudatus roseus._
Red-backed Shrike _Lanius collurio._
Whitethroat _Sylvia communis._
Lesser Whitethroat _Sylvia curruca._
Blackcap _Sylvia atricapilla._
Grasshopper-Warbler _Locustella noevia._
Savi's Warbler _Locustella luscinioides._
Reed-Warbler _Acrocephalus scirpaceus._
Marsh-Warbler _Acrocephalus palustris._
Sedge-Warbler _Acrocephalus schoenobænus._
Willow-Warbler _Phylloscopus trochilus._
Wood-Warbler _Phylloscopus sibilatrix._
Chiffchaff _Phylloscopus collybita._
Song-Thrush _Turdus musicus clarkii._
Redwing _Turdus iliacus._
Blackbird _Turdus merula._
Redstart _Phoenicurus phoenicurus._
Redbreast _Erithacus rubecula melophilus._
Nightingale _Luscinia megarhyncha._
Stonechat _Saxicola rubicola._
Whinchat _Saxicola rubetra._
Wheatear _OEnanthe oenanthe._
Hedge-Sparrow _Accentor modularis._
Wren _Troglodytes troglodytes._
Spotted Flycatcher _Muscicapa striata._
Swallow _Hirundo rustica._
Martin _Delichon urbica._
Sand-Martin _Riparia riparia._
Great Spotted Woodpecker _Dryobates major anglicus._
Lesser Spotted Woodpecker _Dryobates minor._
Green Woodpecker _Picus viridis._
Cuckoo _Cuculus canorus._
Tawny Owl _Strix aluco._
Buzzard _Buteo buteo._
Sparrow-Hawk _Accipiter nisus._
Peregrine Falcon _Falco peregrinus._
Merlin _Falco æsalon._
Kestrel _Falco tinnunculus._
Shag _Phalacrocorax graculus._
Wild Duck _Anas boschas._
Snipe _Gallinago gallinago._
Dunlin _Tringa alpina._
Ruff _Machetes pugnax._
Redshank _Totanus totanus._
Black-tailed Godwit _Limosa limosa._
Curlew _Numenius arquata._
Whimbrel _Numenius phæopus._
American Golden Plover _Charadrius dominicus._
Lapwing _Vanellus vanellus._
Oyster-Catcher _Hæmatopus ostralegus._
Herring-Gull _Larus argentatus._
Kittiwake _Rissa tridactyla._
Razorbill _Alca torda._
Guillemot _Uria troille._
Puffin _Fratercula arctica._
Fulmar _Fulmarus glacialis._
Water-Rail _Rallus aquaticus._
Corn-Crake _Crex crex._
Moor-Hen _Gallinula chloropus._
Coot _Fulica atra._
Wood-Pigeon _Columba palumbus._
Turtle-Dove _Streptopelia turtur._
Partridge _Perdix perdix._
Black Grouse _Lyrurus tetrix britannicus._
Red Grouse _Lagopus scoticus._
TERRITORY IN BIRD LIFE
CHAPTER I
INTRODUCTION
In his _Manual of Psychology_ Dr Stout reminds us that "Human language
is especially constructed to describe the mental states of human beings,
and this means that it is especially constructed so as to mislead us
when we attempt to describe the working of minds that differ in a great
degree from the human."
The use of the word "territory" in connection with the sexual life of
birds is open to the danger which we are here asked to guard against,
and I propose, therefore, before attempting to establish the theory on
general grounds, to give some explanation of what the word is intended
to represent and some account of the exact position that representation
is supposed to occupy in the drama of bird life.
The word is capable of much expansion. There cannot be territories
without boundaries of some description; there cannot well be boundaries
without disputes arising as to those boundaries; nor, one would
imagine, can there be disputes without consciousness as a factor
entering into the situation; and so on, until by a simple mental
process we conceive of a state in bird life analogous to that which we
know to be customary amongst ourselves. Now, although the term "breeding
territory," when applied to the sexual life of birds, is not altogether
a happy one, it is difficult to know how otherwise to give expression to
the facts observed. Let it then be clearly understood that the
expression "securing a territory" is used to denote a process, or rather
part of a process, which, in order to insure success to the individual
in the attainment of reproduction, has been gradually evolved to meet
the exigencies of diverse circumstances. Regarded thus, we avoid the
risk of conceiving of the act of securing a territory as a detached
event in the life of a bird, and avoid, I hope, the risk of a conception
based upon the meaning of the word when used to describe human as
opposed to animal procedure.
Success in the attainment of reproduction is rightly considered to be
the goal towards which many processes in nature are tending. But what is
meant by success? Is it determined by the actual discharge of the sexual
function? So many and so wonderful are the contrivances which have
slowly been evolved to insure this discharge, that it is scarcely
surprising to find attention focused upon this one aspect of the
problem. Yet a moment's reflection will show that so limited a
definition of the term "success" can only be held to apply to certain
forms of life; for where the young have to be cared for, fostered, and
protected from molestation for periods of varying lengths, the actual
discharge of the sexual function marks but one stage in a process which
can only succeed if all the contributory factors adequately meet the
essential conditions of the continuance of the species.
Securing a territory is then part of a process which has for its goal
the successful rearing of offspring. In this process the functioning of
the primary impulse, the acquirement of a place suitable for breeding
purposes, the advent of a female, the discharge of the sexual function,
the construction of the nest, and the rearing of offspring follow one
another in orderly sequence. But since we know so little of the organic
changes which determine sexual behaviour, and have no means of
ascertaining the nature of the impulse which is first aroused, we can
only deal with the situation from the point at which the internal
organic changes reflect themselves in the behaviour to a degree which is
visible to an external observer. That point is reached when large
numbers of species, forsaking the normal routine of existence to which
they have been accustomed for some months, suddenly adopt a radical
change in their mode of behaviour. How is this change made known to us?
By vast numbers of individuals hurrying from one part of the globe to
another, from one country to another, and even from mid-ocean to the
coasts; by detachments travelling from one district to another; by
isolated individuals deserting this place for that; by all those
movements, in fact, which the term migration, widely applied, is held to
denote. Now the impulse which prompts these travelling hosts must be
similar in kind whether the journey be long or short; and it were
better, one would think, to regard such movements as a whole than to
fix the attention on some one particular journey which fills us with
amazement on account of the magnitude of the distance traversed or the
nature of the difficulties overcome. For, after all, what does each
individual seek? There may be some immature birds which, though they
have not reached the necessary stage of development, happen to fall in
with others in whom the impulse is strong and are led by them--they know
not where. But the majority seek neither continent nor country, neither
district nor locality is their aim, but a place wherein the rearing of
offspring can be safely accomplished; and the search for this place is
the earliest visible manifestation in many species of the reawakening of
the sexual instinct.
The movements of each individual are then directed towards a similar
goal, namely, the occupation of a definite station; and this involves
for many species a distinct change in the routine of behaviour to which
previously they had been accustomed. Observe, for example, one of the
numerous flocks of Finches that roam about the fields throughout the
winter. Though it may be composed of large numbers of individuals of
different kinds, yet the various units form an amicable society actuated
by one motive--the procuring of food. And since it is to the advantage
of all that the individual should be subordinated to the welfare of the
community as a whole there is no dissension, apart from an occasional
quarrel here and there.
In response, however, to some internal organic change, which occurs
early in the season, individuality emerges as a factor in the developing
situation, and one by one the males betake themselves to secluded
positions, where each one, occupying a limited area, isolates itself
from companions. Thereafter we no longer find that certain fields are
tenanted by flocks of greater or less dimensions, while acres of land
are uninhabited, but we observe that the hedgerows and thickets are
divided up into so many territories, each one of which contains its
owner. This procedure, with of course varying detail, is typical of that
of many species that breed in Western Europe. And since such a radical
departure from the normal routine of behaviour could scarcely appear
generation after generation in so many widely divergent forms, and still
be so uniform in occurrence each returning season, if it were not
founded upon some congenital basis, it is probable that the journey,
whether it be the extensive one of the Warbler or the short one of the
Reed-Bunting, is undertaken in response to some inherited disposition,
and probable also that the disposition bears some relation to the few
acres in which the bird ultimately finds a resting place. Whilst for the
purpose of the theory I shall give expression to this behaviour in terms
of that theory, and speak of it as a disposition to secure a territory,
using the word disposition, which has been rendered current in recent
discussion, for that part of the inherited nature which has been
organised to subserve a specific biological purpose--strict compliance
with the rules of psychological analysis requires a simpler definition;
let us therefore say "disposition to remain in a particular place in a
particular environment."
But even granting that this disposition forms part of the hereditary
equipment of the bird, how is the process of reproduction furthered? The
mere fact of remaining in or about a particular spot cannot render the
attainment of reproduction any less arduous, and may indeed add to the
difficulties, for any number of individuals might congregate together
and mutually affect one another's interests. A second disposition comes,
however, into functional activity at much the same stage of sexual
development, and manifests itself in the male's intolerance of other
individuals. And the two combined open up an avenue through which the
individual can approach the goal of reproduction. In terms of the theory
I shall refer to this second disposition as the one which is concerned
with the defence of the territory.
Broadly speaking, these two dispositions may be regarded as the basis
upon which the breeding territory is founded. Yet inasmuch as the
survival value of the dispositions themselves must have depended upon
the success of the process as a whole, it is manifest that peculiar
significance must not be attached to just the area occupied, which
happens to be so susceptible of observation; other contributory factors
must also receive attention, for the process is but an order of
relationships in which the various units have each had their share in
determining the nature and course of subsequent process, so that, as Dr
Stout says, when they were modified, it was modified.
Now the male inherits a disposition which leads it to remain in a
restricted area, but the disposition cannot determine the extent of that
area. How then are the boundaries fixed? That they are sometimes adhered
to with remarkable precision, that they can only be encroached upon at
the risk of a conflict--all of this can be observed with little
difficulty. But if we regard them as so many lines definitely delimiting
an area of which the bird is cognisant, we place the whole behaviour on
a different level of mental development, and incidentally alter the
complexion of the whole process. It would be a mistake, I think, to do
this. Though conscious intention as a factor may enter the situation,
there is no necessity for it to do so; there is no necessity, that is to
say, for the bird to form a mental image of the area to be occupied and
shape its course accordingly. The same result can be obtained without
our having recourse to so complex a principle of explanation, and that
by the law of habit formation. In common with other animals, birds are
subject to this law in a marked degree. An acquired mode of activity
becomes by repetition ingrained in the life of the individual, so that
an action performed to-day is liable to be repeated to-morrow so long as
it does not prejudice the existence or annul the fertility of the
individual.
Let us see how this may have operated in determining the limits of the
area acquired, and for this purpose let us suppose that we are observing
a male Reed-Bunting recently established in some secluded piece of marsh
land. Scattered about this particular marsh are a number of small
willows and young alder trees, each one of which is capable of providing
plenty of branches suitable for the bird to perch upon, and all are in a
like favourable position so far as the outlook therefrom is concerned.
Well, we should expect to find that each respective tree would be made
use of according to the position in which the bird happened to find
itself. But what actually do we find--one tree singled out and resorted
to with ever-increasing certainty until it becomes an important point in
relation to the occupied area, a headquarters from which the bird
advertises its presence by song, keeps watch upon the movements of its
neighbours, and sets out for the purpose of securing food. We then take
note of its wanderings in the immediate vicinity of the headquarters,
especially as regards the direction, frequency, and extent of the
journeys; and we discover not only that these journeys proceed from and
terminate in the special tree, but that there is a sameness about the
actual path that is followed. The bird takes a short flight, searches a
bush here and some rushes there, returns, and after a while repeats the
performance; we on our part mark the extreme limits reached in each
direction, and by continued observation discover that these limits are
seldom exceeded, that definition grows more and more pronounced, and
that by degrees the movements of the bird are confined within a
restricted area. In outline, this is what happens in a host of cases. By
repetition certain performances become stereotyped, certain paths fixed,
and a routine is thus established which becomes increasingly definite as
the season advances.
But while it would be quite untrue to say that this routine is never
departed from, and equally profitless to attempt to find a point beyond
which the bird will under no circumstances wander, yet there is enough
definition and more than enough to answer the purpose for which the
territory has, I believe, been evolved, that is to say the biological
end of reproduction. Again, however, the process of adjustment is a
complex one. Habit plays its part in determining the boundaries in a
rough and ready manner, but the congenital basis, which is to be found
in the behaviour adapted to a particular environment, is an important
factor in the situation. For example, if instead of resting content with
just a bare position sufficient for the purpose of reproduction, the
Guillemot were to hustle its neighbours from adjoining ledges, the
Guillemot as a species would probably disappear; or if instead of
securing an area capable of supplying sufficient food both for itself
and its young, the Chiffchaff were to confine itself to a single tree,
and, after the manner of the Guillemot, trust to spasmodic excursions
into neutral ground for the purpose of obtaining food, the Chiffchaff
as a species would probably not endure. All such adjustments have,
however, been brought about by relationships which have gradually become
interwoven in the tissue of the race.
The intolerance that the male displays towards other individuals,
usually of the same sex, leads to a vast amount of strife. Nowhere in
the animal world are conflicts more frequent, more prolonged, and more
determined than in the sexual life of birds; and though they are
acknowledged to be an important factor in the life of the individual,
yet there is much difference of opinion as to the exact position they
occupy in the drama of bird life. Partly because they frequently happen
to be in evidence, partly because they are numerically inferior, and
partly, I suppose, because the competition thus created would be a means
of maintaining efficiency, the females, by common consent, are supposed
to supply the condition under which the pugnacious nature of the male is
rendered susceptible to appropriate stimulation. And so long as the
evidence seemed to show that battles were confined to the male sex, so
long were there grounds for hoping that their origin might be traced to
such competition. But female fights with female, pair with pair, and,
which is still more remarkable, a pair will attack a single male or a
single female; moreover, males that reach their destination in advance
of their prospective mates engage in serious warfare. How then is it
possible to look upon the individuals of one sex as directly
responsible for the strife amongst those of the other, or how can the
female supply the necessary condition? As long as an attempt is made to
explain it in terms of the female, the fighting will appear to be of a
confused order; regard it, however, as part of a larger process which
demands, amongst other essential conditions of the breeding situation,
the occupation of a definite territory, and order will reign in place of
confusion.
But even supposing that the male inherits a disposition to acquire a
suitable area, even supposing that it inherits a disposition which
results indirectly in the defence of that area, how does it obtain a
mate? If the female behaved in a like manner, if she, too, were to
isolate herself and remain in one place definitely, that would only add
to the difficulties of mutual discovery. We find, however, in the
migrants, that the males are earlier than the females in reaching the
breeding grounds, and, in resident species, that they desert the females
and retire alone to their prospective territories, so that there is a
difference in the behaviour of the sexes at the very commencement of the
sexual process. What is the immediate consequence? Since the male
isolates itself, it follows, if the union of the sexes is to be
effected, that the discovery of a mate must rest largely with the
female. This of course reverses the accepted course of procedure. But
after all, what reason is there to suppose that, the male seeks the
female, or that a mutual search takes place; what reason to think that
this part of the process is subject to no control except such as may be
supplied by the laws of chance?
Now, clearly, much will depend upon the rapidity with which the female
can discover a male fit to breed; for if the course of reproduction is
to flow smoothly, there must be neither undue delay nor waste of energy
incurred in the search--some guidance is therefore necessary, some
control in her external environment. Here the song, or the mechanically
produced sound, comes into play, and assists in the attainment of this
end. Nevertheless if every male were to make use of its powers whether
it were in occupation of a territory or not, if the wandering individual
had an equal chance of attracting a mate, then it would be idle to
attempt to establish any relation between "song" on the one hand, and
"territory" on the other, and impossible to regard the voice as the
medium through which an effectual union of the sexes is procured. But
there is reason to believe that the males utilise their powers of
producing sound only under certain well-defined conditions. For
instance, when they are on their way to the breeding grounds, or moving
from locality to locality in search of isolation, or when they desert
their territories temporarily, as certain of the residents often do,
they are generally silent; but when they are in occupation of their
territories they become vociferous--and this is notoriously the case
during the early hours of the day, which is the period of maximum
activity so far as sexual behaviour is concerned. So that just at the
moment when the sexual impulse of the female is most susceptible to
stimulation, the males are betraying their positions and are thus a
guide to her movements. Nevertheless, even though she may have
discovered a male ready to breed, success is not necessarily assured to
her; for with multitudes of individuals striving to procreate their
kind, it would be surprising if there were no clashing of interests, if
no two females were ever to meet in the same occupied territory.
Competition of this kind is not uncommon, and the final appeal is to the
law of battle, just as an appeal to physical strength sometimes decides
the question of the initial ownership of a territory.
I shall try to make clear the relations of the various parts to the
whole with the assistance of whatever facts I can command. I shall do so
not only for the purposes of the theory, but because one so often finds
the more important features of sexual behaviour regarded as so many
distinct phenomena requiring separate treatment, whereas they are
mutually dependent, and follow one another in ordered sequence. I spoke
of the process as a series of relationships. Some of these relationships
have already been touched upon; others will become apparent if we
consider for a moment the purposes for which the territory has been
evolved. Indirectly its purpose is that of the whole process, the
rearing of offspring. But inasmuch as a certain measure of success could
be attained, and that perhaps often, without all the complications
introduced by the territory, there are manifestly advantages to be
gained by its inclusion in the scheme. The difficulties which beset the
path of reproduction are by no means always the same--all manner of
adjustments have to be made to suit the needs of different species.
There are direct relationships, such as we have been speaking of, which
are essential to the every-day working of the process, and others which
are indirect, though none the less important for they must have
exercised an influence throughout the ages. These latter are furnished
by the physical--the inorganic world, by climate, by the supply of the
particular kind of breeding stations, by the scarcity or abundance of
the necessary food and by the relative position of the food supply to
the places suitable for breeding. Why does the Reed-Bunting cling so
tenaciously to an acre or more of marshy ground, while the Guillemot
rests content with a few square feet on a particular ledge of rock? The
answer is the same in both cases--to facilitate reproduction. But why
should a small bird require so many square yards, whilst a very much
larger one is satisfied with so small an area? The explanation must be
sought in the conditions of existence. The Reed-Bunting has no
difficulty in finding a position suitable for the construction of its
nest; there are acres of waste land and reedy swamps capable of
supplying food for large numbers of individuals, and the necessary
situations for countless nests. But its young, like those of many
another species, are born in a very helpless state. For all practical
purposes they are without covering of any description and consequently
require protection from the elements, warmth from the body of the
brooding bird, and repeated supplies of nourishment. A threefold burden
is thus imposed upon the parents: they must find food for themselves,
they must afford protection to the young by brooding, and they must
supply them with the necessary food at regular intervals. And their
ability to do all this that is demanded of them will be severely taxed
by the brooding which must perforce curtail the time available for the
collection of food.
Let us then suppose that the Reed-Buntings inhabiting a certain piece of
marsh are divided into two classes, those which are pugnacious and
intolerant of the approach of strangers, and those which welcome their
presence. The nests of the former will be built in isolation, those of
the latter in close proximity. In due course eggs will be laid and
incubation performed, and thus far all alike will probably be
successful. Here, however, a critical point is reached. If the young are
to be freed from the risk of exposure, the parents must find the
necessary supply of food rapidly. But manifestly all will not be in a
like satisfactory position to accomplish this, for whereas the isolated
pairs will have free access to all the food in the immediate vicinity of
the nest, those which have built in proximity to one another, meeting
competition in every direction, will be compelled to roam farther
afield and waste much valuable time by doing so; and under conditions
which can well be imagined, even this slight loss of time will be
sufficient to impede the growth of the delicate offspring, or to lead
perhaps to still greater disaster. If any one doubts this, let him first
examine one of the fragile offspring; let him then study the conditions
under which it is reared, observing the proportion of time it passes in
sleep and the anxiety of the parent bird to brood; and finally let him
picture to himself its plight in a wet season if, in order to collect
the necessary food, the parents were obliged to absent themselves for
periods of long duration.
Now take the case of the Guillemot. Its young at birth are by no means
helpless in the sense that the young Reed-Bunting is, and food is
readily procured. But breeding stations are scarce, for although there
are many miles of cliff-bound coast, yet not every type of rock
formation produces the fissures and ledges upon which the bird rests.
Hence vast stretches of coast-line remain uninhabited, and the birds are
forced to concentrate at certain points, where year after year they
assemble in countless numbers from distant parts of the ocean. If, then,
different individuals were to jostle one another from adjoining
positions, and each one were to attempt to occupy a ledge in solitary
State, not only would the successful ones gain no advantage from the
additional space over which they exercised dominion, but inasmuch as
many members that were fitted to breed would be precluded from doing
so, the status of the species as a whole would be seriously affected.
The amount of space occupied by each individual is therefore a matter of
urgent importance. A few square feet of rock sufficient for the
immediate purpose of incubation is all that can be allowed if the
species is to maintain its position in the struggle for existence.
Our difficulty in estimating the importance of the various factors that
make for success or failure arises from our inability to see more than a
small part of the scene as it slowly unfolds itself. The peculiar
circumstances under which these cliff-breeding forms dwell does,
however, enable us to picture, on the one hand, the precarious situation
of an individual that was incapable of winning or holding a position at
the accustomed breeding station, and, on the other, the plight of the
species as a whole if each one exercised authority over too large an
area. With the majority of species it is difficult to do this. So many
square miles of suitable breeding ground are inhabited by so few
Reed-Buntings that, even supposing certain members were to establish an
ascendency over too wide an area, it would be impossible to discover by
actual observation whether the race as a whole were being adversely
affected. Competition doubtless varies at different periods and in
different districts according to the numerical standing of the species
in a given locality and according to the numerical standing of others
that require similar conditions of existence; at times it may even be
absent, just as at any moment it may become acute. These examples show
how profoundly the evolution of the breeding territory may have been
influenced by relationships in the inorganic world, and they give some
idea of the intricate nature of the problem with which we have to deal.
I mentioned that the first visible manifestation of the revival of the
sexual instinct was to be found in the movements undertaken by the males
at the commencement of the breeding season. Such movements are
characterised by a definiteness of purpose, whether they involve a
protracted journey of some hundreds of miles or merely embrace a parish
or so in extent, and that purpose is the acquirement of a territory
suitable for rearing offspring. They are thus directly related to the
territory, and the question arises as to whether their origin may not be
traced to such relatedness. So long as we fix our attention solely upon
the magnitude of the distance traversed the suggestion may seem a
fanciful one. Nevertheless, if the battles between males of the same
species _are_ directly related to the occupation of a position suitable
for breeding purposes, if those which occur between males of closely
related forms _can_ be traced to a similar source, if the females take
their share in the defence of the ground that is occupied, if, in short,
the competition is as severe as I believe it to be, and is wholly
responsible for the strife which is prevalent at the commencement of the
breeding season--then such competition must have introduced profound
modifications in the distribution of species; it must have even
influenced the question of the survival of certain forms and the
elimination of others; and since the powers of locomotion of a bird are
so highly developed it must have led to an extension of breeding range,
limited only by unfavourable conditions of existence.