SUGGESTIONS AND GUESSES
Several important migration phenomena have hardly been touched upon in
the previous pages; a few words about these may not be out of place.
There is no doubt that now and again American species are met with in
Europe, and European in America, though there is no evidence of direct
regular trans-Atlantic passage, except from Greenland. The appearance of
these birds has been explained in several ways, the general notion being
that it is impossible for a bird to fly unaided across the Atlantic, say
over 3000 statute miles, without rest. In considering the question we
are met with various points on which we still lack knowledge.
We know that strong-winged waders can accomplish 2500 miles, apparently
without a rest, and that if rest is necessary these birds can swim and
rise from the waves. We know, too, that there is regular passage between
Greenland and Europe. We do not know how long a bird can, without rest
and food, sustain flight; we do not know the speed it can travel when
aided by favourable winds, nor to what extent even passerine birds may
rest upon the water. My friend Mr J. A. Dockray, when punting in the
Dee estuary, has often seen birds alight to rest on his punt, and once
saw a tired thrush settle repeatedly on the water and finally safely
cross the estuary. There are several instances recorded of passerine
birds alighting upon and rising again from the water.
We do not know the extent of Greenland as a summer breeding home of
birds; the growing knowledge of this vast continent proves that its
summer avifauna is much larger than we thought, and that western and
eastern forms inhabit adjacent breeding areas; the possibility of birds
banding with the wrong set of travellers is greater than was suspected.
It is urged that the western shores of Scotland and Ireland should
receive these stragglers, but that the records of American birds
are fewer from these coasts than from the eastern shores and even
Heligoland. The best island route, however, would lead birds to join
the travellers from Scandinavia which pass by the safer eastern route
than the one round the western wind-swept shores of Ireland. Even this
reputed scarcity may be error, for how many reliable watchers are there
compared with the immense length of this wave-indented coastline? How
easy for a straggler to be overlooked! Mr S. F. Baird, in his paper on
the "Distribution and Migration of North American Birds," is emphatic
that the transfer of American birds to Europe is entirely due to the
agency of winds carrying them from their course (6). Mr A.L. Butler
met with snow-buntings in mid-Atlantic travelling east, and Mr J.
Trumbull supplies information about many passerine birds--especially
snow-buntings and wheatears--seen in September and October at various
points between Canada and the British coasts (53). Some joined ships
but others made no attempt to do so, even at 54° north 44° west.
Unfortunately there is the negative evidence of fraud, for when
unscrupulous dealers found that the public would give high prices for
rare birds, a trade in American skins began. It is not impossible that
even Gätke was victimised. Error or even accidental fraud may be taken
into account. Some years ago I heard that a hawk-owl had been killed
in Cheshire, at an inland port on the Ship Canal; I traced the bird,
the American species, but discovered that it had been captured on an
east-bound steamer in the Straits of Belle Isle, and had only died or
been killed when the vessel reached the coaling station at Partington,
where the taxidermist who received it thought it had been taken. A Cape
pigeon, which I saw in the flesh, reported as shot in Lancashire, I
found had been brought home in cold storage.
Birds may be carried on shipboard. When the "Mauretania" was between
400 and 500 miles out from New York, bound eastward on June 15th, 1911,
a curlew came on board and remained for three days, leaving when the
Irish shores were sighted on the 18th. My informant, an experienced
wildfowler, failed to catch the bird, but described it as like our
curlew. Probably it was the American _Numenius longirostris_, but
amongst the Irish curlews it would easily remain unrecognised.
When a seabird appears inland the usual explanation given is
"storm-blown," but increasing knowledge shows the frequent fallacy of
this idea. The Manx shearwater, for instance, is a regular migrant, and
the examination of the dates of the records of so-called "storm-blown"
birds found in inland localities, shows a remarkable regularity; the
majority are met with between the end of August and the end of the first
week in September. Not only do the birds move south in the early days of
September but many, usually at any rate, cross England; the weaklings
fall out and are found. Is it possible that some of these collapses of
passing birds are due to more than mere physical fatigue? Aviators have
discovered the existence of "wind pockets" or "holes in the air," where
the resistance of the air appears suddenly to fail; what is the effect
on a flying bird which suddenly enters one of these pockets?
The lesser black-backed gull also crosses England in large numbers; its
movements are more noticeable than those of the herring gull, common
gull, or even of the inland nesting and inland feeding black-headed gull.
Recent investigation has added the yellow-browed warbler, the
blue-throat, and many other "rare," or "casual" passerine birds to the
list of regular British birds of passage; evidently they have been
overlooked before. Even the crossbill, so long classed as a spasmodic
invader, is now seen to be a regular bird of passage to Britain, though
in varying numbers, and quite independently of the sub-specific form
which is always with us.
The wanderings to our islands of southern petrels and other oceanic
birds has occasioned much surprise. Take two examples of the genus
_Oestrelata_, one _O. brevipes_ taken at Borth in 1889, and _O.
neglecta_ in Cheshire in 1908, the known breeding range of both being in
the western Pacific; pelagic wanderings might lead a bird anywhere, but
it is conceivable that investigation may show that the breeding area is
wider than is supposed and that these species have stations even in the
South Atlantic.
Some writers affirm that birds only migrate on the wing, but the journey
by sea of many species is varied in method. Those very regular migrants,
the puffins and guillemots, which the light keepers assure us leave and
return to their stations almost at fixed dates, move by slow nautical
stages, swimming and feeding as they go. On May 2nd, 1911, I watched
a red-throated diver slowly travelling north; it actually travelled
farther beneath the surface than either by swimming or flying, so long
as I had it in view. The penguin's migrations cannot possibly be on
the wing. Dr Brooks rightly contended that the periodic assemblage of
wandering sea-birds at their "rookeries" is true migration, regular
as the almanack, although the feeding area is immense and the birds
do not reach home by any single path. Seebohm tells us of young bean
geese migrating in full moult, marching in an army to the interior of
the Tundra, and Mr W. H. Hudson, in "Birds and Man," relates a pathetic
story of a pair of upland geese in southern Buenos Ayres. His brother
saw them in August, the early spring of South America, leaving the
plains where they had wintered to breed in Magellanic islands. The main
flocks had departed, but these two birds, the female with a broken wing,
were steadily moving south, the male taking short flights and waiting
for her, as if to urge her on, and the female walking. "And in this
sad, anxious way they would journey on to the inevitable end, when a
pair or family of carrion eagles would spy them--and the first would be
left to continue the journey alone."
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