THE PERILS OF MIGRATION
The dangers to which migratory birds are subjected during their journeys
are but little less than those which would befall them if they remained
in unsuitable zones. During long oversea passages fatigue and hunger
weed out the weaklings, sudden storms and adverse winds strike them
where no land is near, and they are carried often far from the goal
they aimed at. Predatory birds accompany them, taking toll _en route_,
and predatory man waits for the tired wanderers with gun and net. Shore
birds may rest upon the waves; sandpipers have been seen feeding as
they walked upon the drifting weed of the Sargasso Sea, and steamers
and other vessels frequently provide a rest for weary birds; but what
happens to the many which find no haven? "Woe to the luckless warbler
whose feathers once become water-soaked!--a grave in the ocean or a
burial in the sand of the beach is the inevitable result," says Mr
Cooke. A storm on Lake Michigan during spring migration piled many
birds along the shore, and in the wider Gulf of Mexico many hundreds
of passage birds were seen to fall into the water when caught, but 30
miles from land, by a violent "norther." Other similar sudden disasters
have been recorded off our British coasts, even so far back as 1786,
when, as quoted by Southwell, a Newcastle collier passed through water
off the Suffolk shores black with vast numbers of drowned woodcocks.
During normal migration birds may be brought to a lower elevation by
strong contrary winds, or they may be bewildered by fogs and cloud and
dropped nearer the surface; it is then that the travellers meet with
disaster at our coastwise lights.
Mr Tomison records some of his experiences of migration at Skerryvore
(52). He never saw a bird at the windows when the moon was shining,
and on clear nights the passing crowds go on without a pause. But on
hazy nights, with an easterly wind and drizzle, or during fogs, if
large numbers of migrants are passing, hundreds may be seen flying in
all directions, "all seemingly of the opinion that the only way of
escape out of the confusion--is through the windows of the lantern."
On one September night, when he was standing on the balcony, he likens
the appearance of the birds to a heavy fall of snow. "Thousands were
flitting about; hundreds were striking against the dome and windows;
hundreds were sitting dazed and stupid on the trimming paths; and
scores falling to the rocks below, some instantaneously killed, others
seriously injured, falling helplessly into the sea." On the following
night when many fieldfares, redwings, thrushes and other birds were
passing, he says--"Sometimes we use the terms hundreds and thousands
without thinking what these figures mean but on this occasion when I say
thousands were killed I do not exaggerate in the slightest."
Mr W. Brewster's account of his experiences at the Point Lepreaux
lighthouse (8), shows that similar disasters occur in Canada and the
States, as indeed they do wherever there are passages of birds. On a
foggy evening in September 1885 "as soon as the sky became overcast
small birds began to come about the light--with the advent of the fog
they multiplied tenfold in the course of a few minutes" and many struck.
"About the top of the tower, a belt of light projected some thirty yards
into the mist by the powerful reflectors; and in this belt swarms of
birds, circling, floating, soaring, now advancing, next retreating,
but never quite able, as it seemed, to throw off the spell of the
fatal lantern.... Dozens were continually leaving the throng" of birds
which had flown to leeward, "and skimming towards the lantern. As they
approached they usually soared upward, and those which started on a
level with the platform usually passed above the roof.... Often for a
minute or more not a bird would strike. Then, as if seized by a panic,
they would come against the glass so rapidly ... that the sound of the
blows resembled the pattering of hail." During his stay no birds came to
the light except during dense cloud or fog, and they came in greatest
numbers when an hour or two before the fog the sky was clear.
The experiences of Eagle Clarke, Seebohm and others who have spent
migration seasons at lighthouses might be quoted, but these two give a
vivid description of what regularly takes place when weather conditions
are unfavourable. Steady white lights are the most fatal to migrants,
revolving lights, if white, are struck by some birds, but red lights
seldom attract the passers. Mr Eagle Clarke thinks that birds are
actually decoyed from their path and arrested in their course by the
action of the lights; he says that a change from white to red lights at
the Galloper Lightship stopped bird attraction.
On the mainland a new high building or tower, new telegraph wires or
other erections, until their presence is familiar, take toll of passage
birds.
Mr R. M. Barrington has for years collected information from the Irish
lighthouses and light-vessels; some of his results were added to the
work of the British Association Committee, and some he published himself
(5). He emphasises the fact that these phenomena depend largely upon
weather, and therefore are not trustworthy indications of the density
at any time or place of migration. Out of 115 song thrushes killed at
the lights and sent to him, 80 per cent struck during the fourth and
first quarters of the moon, and the same rule holds good for other
species. The intimate relation between the lunar phases and the number
of examples killed was shown by statistics from 1888 to 1894. Out of 673
specimens received only 116 were killed when the moon was more than half
full.
Apart from fog or cloud, birds may fail to hit the land aimed at, either
through accidental divergence from correct direction or wind drift. In
November 1884 Mr Barrington received information of large numbers of
rooks passing simultaneously at the Tearaght and Skelligs Lights--island
stations 20 miles apart and each 9 miles off the Kerry coast. The birds
arrived in continuous flocks from the westward--the open Atlantic--and
passed in an easterly and landward direction; they came in small parties
and in flocks numbering two or three hundred, on many days between the
2nd and 25th of the month. A few birds were noticed at the same time at
stations on the south and east Irish coasts, and all alike making for
the land. From similar observations made in other years he concludes
that these were portions of hosts which had overshot the mark, and
failing to find land had turned back. The weather charts, he adds,
show no sufficient reason for the birds to have been blown out of their
course by storms.
The weather charts, as I have pointed out, do not indicate the force
or direction of the wind at high altitudes; I suggest that these birds
were carried rather than blown out of their way by strong currents at a
higher altitude than recorded on the charts, and that having left the
air currents they descended to the elevation of about 700 or 800 feet at
which most of them were flying when they were observed making for the
land.
On the night of March 29th to 30th, 1911, the south-eastern extremity of
Ireland experienced a remarkable rush of migrants, and the local papers
were full of the avian disaster, for large numbers of birds struck
the lights as well as buildings and other objects in inland towns. Mr
Barrington collected information (4), and found that most of the birds
were starlings, though thrushes, blackbirds, and redwings were numerous.
He received specimens of woodcock, water-rail, snipe, dunlin, meadow
pipit, wheatear, goldcrest, starling, song thrush, redwing, blackbird,
black redstart, robin, skylark, and stonechat, whilst some thirteen or
fourteen other species were said to have been recognised, amongst them
oyster-catcher and wild duck. The area affected lay south-east of a line
drawn across country from Balbriggan to the Old Head of Kinsale, with
a coast line of some 200 miles; most of the birds noticed inland were
at towns on the rivers Suir, Barrow, and Nore. The flight was mostly
north-east, and at the lights offshore, towards the land. Mr Barrington
gives the following explanation. After crossing the Channel the coast
of Wexford was reached and the stream divided, some going north along
the east coast and others westward along the south coast, but changing
their direction when they reached the wide mouth of the Barrow. The
flocks which passed Lucifer Shoals, 10 miles offshore, proceeded north
without touching Wexford. Northerly and easterly winds had prevailed for
weeks prior to the 29th over France and the British Islands, and birds
would be held up in southern Europe; the milder coastwise temperature
of western France, he thinks, would cause them to take a more westerly
course than usual. On the morning of the 29th the wind changed to the
south at Valentia, Pembroke and the Scilly Islands, and there was an
average rise of 7° in temperature at French stations. This rise and the
southerly wind liberated the birds, but as the wind continued north-east
or east in England they "decided" to take a longer and more exhausting
course than usual, pass to Ireland and then turn north-east. The change
took place exactly on the last day of the last quarter of the moon--the
darkest night for travel. A bank of fog and drizzle met them off the
Irish coast, and baffled and weary they were attracted by the lights,
not only on the coast but in the inland towns they passed.
In the main I think Mr Barrington's explanation is correct, but even if
the birds were gathered farther west than usual, which I doubt, it was
the north-east wind which had drifted them, and the word "decided" is a
bold one to use when dealing with the behaviour of birds. Easterly winds
would drift them westward, and the striking Ireland was accidental; it
was the safety of the many, as well as the deathblow to the comparative
few. On the night of the 31st I received news of this visitation, and
later found that similar movements, without disaster, were noticed
on the north coast of Wales and in Cheshire. On the nights of the
30th and 31st birds in large numbers passed over Bangor and the Menai
Straits; amongst them were golden plover, and the next day these birds
with fieldfares and redwings were more abundant than before in the
mid-Cheshire fields. On the night of April 2nd, from dusk to midnight,
a large passage occurred over Mere in Cheshire, where curlew, golden
plover, oyster-catcher and wild duck were recognised by their calls,
and at the same time a passage was observed at Old Colwyn on the Welsh
coast. I do not even suggest that these were the same birds which passed
over south-eastern Ireland, but their presence within so short a time,
indicates the volume of the movement.
Welsh papers recorded an "Extraordinary feathered catastrophe" at
Pwllheli in Cardigan Bay which occurred on the night of March 17th,
1904, in which "thousands" of birds fell dead and dying upon the town
and shore. The journalistic description was lurid, but I am able to
give the explanation sent to me by a friend who was an eye-witness. The
night had been dark and foggy, and in the morning he found "scores of
dead starlings, redwings, thrushes and blackbirds lying on the beach at
high-water mark." During the night a steamer had been loading setts at
the quarry at the Gimlet Rock, a large outcrop outside the harbour, and
the artificial light used had been one of the powerful oil flares. The
fog-bewildered birds were led astray and had struck masts, rigging, and
rock in their confusion.
During a big fire in Philadelphia on March 27th, 1906, Mr W. Stone saw
large numbers of birds passing in its illumination, and many passed
too near and fell into the blaze; he picked up a few half-burnt song
sparrows and juncos.
Blizzards on continents, and to a less extent snow-storms in our
islands, account for the death of thousands of travellers. And even
in most favourable weather birds fall exhausted. During a stay on the
Yorkshire coast in autumn, when migration was even-flowing and unchecked
by adverse weather, I found several goldcrests which had reached land
only to die, and though most birds came in without showing signs of
fatigue, a few larks and starlings were so tired that they made little
effort to escape when approached.
Ornithological literature supplies many accounts of more or less similar
disasters to migrating birds, but these are enough to show that the
perils of migration are not exaggerated.
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