The clear air of Skomer, above the level of the
cliff-tops, was by day always filled with the large wheeling white
forms and loud wailing cries of the gulls. They were an essential
part of the liveliness and beauty of the island summer, just as
they formed an important part of the complex ecology of the
island's natural life.
It is interesting to find that the Rev. M. A. Mathew, in The Birds
of Pembrokeshire, published in 1894, attributed the increase of
gulls on Skomer to the passing of the Sea Birds' Preservation Act.
He notes that on Skomer 'All day long herring-gulls may be observed
quartering the island in their vigilant quest after young rabbits;
they frequently dig them out of the stops.' He found that 'a colony
of lesser blackbacked gulls had a station on the summit, and we
were able to walk among their nests'. He does not record great
black-backed gulls on Skomer. Three years later Robert Drane,
F.L.S., visited Skomer and wrote the paper A Pilgrimage to Golgotha
which we have already referred to. He found (May-June 1897) that
there were (an unspecified number of) great black-backed gulls
nesting, and he jocularly describes the bird as a coward, fool and
tyrant.
As the farming of the island was gradually abandoned early in the
present century the gulls increased. The central fields, falling
out of cultivation, provided new nesting sites for the lesser
black-backed gulls, as well as new ground for burrowing rabbits and
seabirds. But no accurate census work was carried out on Skomer
until 1945, when Messrs. C. W. G. Paulsen, H. H. Davis and M.
Gurteen visited the island from May 25th to June 4th. Their census
of the gulls may be compared with ours of 1946:
Pairs of
|
Herring Gull
|
L.B.B.
|
G.B.B
|
Kittiwake
|
1945
|
c. 660
|
c. 1,090
|
c. 40
|
c. 1,500
|
1946
|
c. 700
|
c. 1,000
|
60
|
1,909
|
.
The great black-backed and kittiwake gulls alone
could be counted with accuracy - they were distinctive in form and
habitat. The herring and lesser black-backed gulls were too mingled
one with the other for us to be able to assess their numbers
separately with a greater degree of accuracy than to the nearest
round figures. With every large colony of lesser black-backs on the
plateau of the island there were roughly 5 per cent. of
herring-gulls, and with some but not all of the large groups of
herring gulls on the cliffs there were a few pairs of lesser
black-backs.
This mingling is characteristic of the gull colonies on Skokholm
and other breeding places of the lesser black- backed gull. The
eight main lesser black-back communities were sited where the
annual vegetation was fairly tall; the bracken-bluebell association
was preferred, but not exclusively. There was one colony in the
heather- ragwort community near the Garland Stone, with many
herring-gulls in it. In these lesser black-back colonies the
herring-gulls usually though not invariably placed their nests
against rock or loose stones, sometimes against a stone-banked
hedge-wall, which seemed to serve the purpose of a look-out perch,
as well as - to the observer - a link with the rocky cliff which is
their normal habitat on Skomer. Similarly, the lesser black-backs
nesting on cliff slopes among the herring-gulls usually placed
their nests in vegetation. Thus in the lush vegetation of the
ledges of the north-east coast, from Garland Stone to North Castle
Point, lesser black-backed gulls were almost as numerous as
herring-gulls, but they were absent or very scarce on the bare
exposed cliffs of the south-west.
The great black-backed gulls had settled in pairs occupying the
rocky outcrops, headlands and islets, when we first landed in
March. We counted exactly 60 pairs of this large gull, but its main
breeding ground was on the top of Middleholm where it was estimated
that some loo pairs nested in 1946. The reason for this
concentration on the 22 acres of Middleholm seemed obvious to us.
On Skomer, because of the slaughter this gull does among other
seabirds, it was (and had always been since its increase within the
last two decades) the subject of persecution by the human occupants
of and visitors to the island, not so much by shooting (though a
little of this had been done before the war) as by the constant
collection of its eggs. We are informed that previous owners of the
island collected the eggs when fresh, and destroyed them when too
far incubated to be used as human or stock food. But Middleholm has
been visited on few occasions in recent years (we ourselves only
visited it four times in 1946- April 3rd and 4th, May 26th, and
August 22nd), and there the great black-backs have concentrated, to
breed in comparative peace. The owners of the island were
astonished to learn from our records that there were nearly twice
as many great gulls breeding on Middleholm as on Skomer, and they
vowed to pay more attention to collecting their eggs on Middleholm
in future.
Although we had come to Skomer as observers with no plan to do more
than watch and record, we found ourselves sufficiently influenced
by the feeding-habits of the great black-back, which caused such
general indignation in our visitors, to agree that something should
be done about controlling its increase. Fortunately it was
perfectly easy for us to agree to the collecting of its eggs on
grounds acceptable to such scientific conscience as we might
possess as wardens of a study centre. These eggs were most useful
as food, and as the eggs of the domestic hen were still rationed
and difficult to obtain, we gladly consented to the collection of
great black-backed gulls' eggs, and also to the taking of the eggs
of lesser black-backed and herring-gulls in certain colonies set
aside for that purpose. As a result, although no exact record was
kept, something like fifty gulls' eggs a day were collected during
May and June, that is, about 3,000; many of these were put down in
pickle to be used later in the summer. In addition, several hundred
were collected by local farmers and fishermen who made their annual
egging excursion to Skomer late in May.
How far this regular egg-collecting (for it has gone on for many
years now; even during the war gulls' eggs were collected on both
Skokholm and Skomer) has affected the numbers of breeding gulls it
is impossible to measure. The undoubted increase of the great
blackbacked gull locally may be associated with the increase of
rabbits and burrow-nesting birds which followed the decay of
farming on the islands. It has been shown, however, that the great
black-backed gull 'as a breeding species has increased in the last
thirty years' all round the coasts of the British Isles. In
Pembrokeshire the development of Milford Haven as a fishing and
trawling port has provided all three breeding gulls with the
opportunity of almost unlimited food in the form of fish- heads and
offal. Hundreds of all three species of gulls, but especially of
herring gulls, throng the quayside market, and there is food for
all - in fact so much food is available that it is observable that
the scavengers are at times quite dainty in their selection of
tit-bits, ignoring coarse and bony fish and fish-heads.
Many of these gulls are in immature plumage in summer, but numbers
are fully adult. There appears to be a definite flight-line between
Skomer and Milford Haven; especially in the evenings are great
numbers, chiefly of herring-gulls, seen to return westwards along
the haven towards Dale and St. Brides and thence along the outer
coasts across Jack Sound to Skomer. This movement continues long
after the breeding season, and is then apparently due to gulls
returning to the safety of the islands, especially uninhabited
Middleholm, to roost for the night. This local movement might be a
line for research in the future; it could be studied by catching
and ringing (and colourmarking too) adults at Milford Haven
fish-market, combined with the trapping and ringing of adults at
the nest. Stephen Marchant demonstrated the ease with which gulls
can be trapped on Skomer by means of a wire cage placed over the
nest (containing eggs) with a funnel or lobster-pot-type entrance;
he found that in many cases the adult returned within a few
minutes, or as soon as the observer was out of sight, and it
quickly found the entrance to the cage, but was unable to find the
exit afterwards. After being ringed and released the bird did not
immediately return to the nest, but its mate usually took its
place, and it was thus possible to ring the pair within an hour or
two of setting the trap. This technique is of course not new; it
has been used extensively in ornithological experiments with many
species all over the world. It is possible that these gulls, and
especially herring-gulls (because they are the least migratory and
the most familiar with the country near their breeding grounds),
unable to obtain sufficient food on Skomer, may visit Milford Haven
from time to time during the breeding season, and obtain there
sufficient food to last several days. We suspect that, except when
feeding young, gulls, like shearwaters and other seabirds, are able
to fast for long periods, probably several days, after gorging or
filling their stomachs with a heavy meal. And perhaps because it is
the most migratory and therefore presumably the least familiar with
the topography of Pembrokeshire, the lesser blackback, the most
abundant gull on Skomer, is most scarce of the three at Milford
Haven during the breeding season.
The vast breeding population of approximately 4,000 adults of the
three predatory gulls on Skomer cannot be supported entirely on the
limited number of chicks and eggs of other seabirds, plus the
rabbits, which are available if the populations of these food
species are to maintain their numbers year by year. We can only
give quite hypothetical figures of this food estimated to be
available during one season and the following table is intended
purely as a guide, compiled out of our knowledge of the mortality
in these species caused by predatory gulls:
- from
1,909 pairs of kittiwakes probably 1,000 chicks or eggs
- from
2,500 pairs of razorbills, probably 1,000 chicks or eggs
- from
3,000 pairs of guillemots, probably , 1,500 chicks or eggs
- from
50,000 pairs of puffins , probably 5,000 adult or young
- from
25,000 pairs of shearwaters, probably 2,500 adult or young
- from
5,000 doe rabbits, probably 10,000 young rabbits
or sufficient food to provide about ten good meals in a season for
each adult gull-allowing a proportion to buzzards, ravens and
crows.
Of course these meals are not 'rationed' equally
in this way. We know that the great black-back takes the majority
of adult and young birds and the larger young rabbits. The other
two gulls are egg thieves and slayers of small rabbits and baby
chicks. We have remarked before that a great number of the eggs and
very young gull chicks, at least of the herring and lesser
black-back gulls, are killed, often cannibal-wise, by all three
species. Quite well-grown (i.e. partly feathered) herring and
lesser black-back chicks are killed by the great black-back,
especially late-born chicks which are still small in August, when
the fledging of the chicks of the cliff-nesting auks deprives the
great gull of a source of food. The mortality among young gulls
from this and all other causes is very heavy and we estimated that
the percentage of young gulls which reached complete juvenile
plumage and were able to fly on Skomer in 1946 was very low,
probably not more than l0 per cent. of the number of breeding
birds.
It was not very safe to ring the half-grown nestlings of the
herring and lesser black-back gulls as they resembled each other so
closely and the two species were nesting in the same community. But
it was possible to catch a number of old birds with nest-traps as
mentioned earlier, and also, on nights of dense fog, breeding
adults could be, caught by dazzling them at the nest with a
powerful torch. It was interesting to find that these gulls, which
apparently can find their way across mist-covered sea so easily,
were, like small migratory birds at lighthouses on misty nights,
helpless in the light of a torch on a really foggy night, and made
little attempt to fly or, if they did, they could be seized in the
air, so feebly did they move then. On dark nights without mist,
however, they were too nimble to catch, and seemed to see the
approaching human being from some distance.
In the early hours of April 29th, 1946, a night of heavy mist, we
caught fifteen adult lesser black-backs (to say nothing of one
surprised rabbit) with the aid of torches. Of these one was
recovered at Portimao, southern Portugal on February 15th, 1947,
and a second at Baracaldo, northern Spain, on November 2nd,
1947.
Comparatively few immature gulls were present
during the breeding season, so few in fact that observers were
moved to make special notes on their occurrence. This was
especially true of the kittiwake, only few individuals of which
were recorded in the striking yearling or 'tarrock' plumage; the
latest on June 16th.
The kittiwakes were last of all to nest, although they were seen to
be flying below the cliffs even in March. Not until late in May did
they begin seriously to build their small platforms on the
scarcements of the sheer rock face, usually above fairly deep
water. Nearly a thousand pairs thronged the great wall of the Wick,
and never ceased to provide wonder and joy to the observer until
they departed late in August. Kittiwakes seem to prefer working in
concert, even calling in concert. The great chasm of the Wick would
suddenly resound with a fresh outburst of their wailing cries which
would rise above the growling undertones of the guillemots; and as
suddenly there would be almost complete silence. In May the
kittiwakes made communal sorties to gather thrift and grass from a
selected spot on the cliff, attacking the herbage with excited
mewings like a crowd of schoolboys flinging themselves at the
window of a tuckshop. The mouthful of grass or thrift would be
carried to the nest and there padded down by the bird which had
remained to guard the site. Sometimes the nesting material was
cemented with what appeared to be mud. The log-book records for May
22nd: 'One kittiwake appeared to be carrying all the nesting
material including mud, while the other remained standing in the
nest. The mud-carrier, after depositing mud on the sides of the
nest, stooped over the mud with wide-open bill, and appeared to be
in the act of exuding some form of moisture. The action was
accompanied by a quick padding of the feet by both birds, to
consolidate the walls of the nest. After the mud-carrier had left
the nest, the remaining bird continued the paddling action.' Mating
at the nest followed. Laying continued well into June, at the end
of which month the first chicks were born.
Herring-gulls persecuted the kittiwakes, even impudently pouncing
upon the nest while the owner was sitting, in the effort to
dislodge the sitter and seize egg or chick. Great black-back gulls
would take larger chicks and gulp them down whole. Out of ten nests
under daily observation from July 4th onwards, containing at that
date sixteen new-born chicks or near-hatching eggs, Joan Keighley
observed that only two chicks reached the flying stage. This
accurate record gives us a figure of ten chicks reared to each
hundred adults, and unless the kittiwake is (for a bird) very
long-lived, this margin is insufficient for the maintenance of
kittiwake numbers (but, of course, it is not possible to generalise
from one small sample). These chicks remained in the nest
approximately forty- four days.
The last breeding seabirds to be noted are the cormorant and shag,
and because they nested in rather inaccessible situations and in
very small numbers very little work was done on these species. One
colony of cormorants has nested in most years (but not in 1898 or
1947) on the top of the Mew Stone where in I946 some twelve pairs
were breeding. Ben Hawkins seems to have adopted this colony for
special observation; perhaps, as others suggested to him, he
enjoyed the feeling of seclusion which a visit to the Mew Stone
gave him. He swam to the rock on June 13th, July 6th and August
19th, and ringed young cormorants. Asked to give an account of his
observations on the first occasion, he reported twelve young
cormorants hatched of which three were old enough for him to ring.
He added (in the log- book): 'It is remarkable what details escape
the notice of an untrained observer whose trousers and luncheon and
future are on the farther shore.'
There were very few shags nesting on Skomer, although many adults
and immatures fished close inshore and rested with wings extended
on the cliffs and outlying rocks. In the Lantern Cave at the east
end of the island, high up on ledges in the darkness of this arch
through which the tides flow from south to north at high water,
three or four pairs nested. There were three other pairs in dark
crannies elsewhere on the Neck. On Middleholm ten pairs nested in
like situations; some of these had the honour of being sketched by
Charles Tunnicliffe, A.R.A., when he spent several hours on the
holm on May 26th