Gulls & Cormorants
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