The Zoologist/4th series, vol 6 (1902)/Issue 732/The Black-headed Gull (''Larus ridibundus''). Some Modifications of Habits

by Robert Service

 

THE BLACK-HEADED GULL (LARUS RIDIBUNDUS).
SOME MODIFICATIONS OF HABITS.

By Robert Service.

 

For the most part lacustrine in its nesting habits, the Black-headed Gull is yet by no means unknown as a strictly sea-shore species at the breeding season. One small colony that varies from season to season from sometimes only a dozen pairs to over a hundred pairs has bred annually for many years on one part or another of the grassy salt merses of the Solway to westwards of the Nith estuary.

One season this particular colony had its nests destroyed by a succession of high tides in May, whereupon the birds shifted over the sea-bank to a turnip field, and betwixt the rows of young turnips built fresh nests of sea-wrack brought from tide-marks, and successfully brought off their young. Such modifications of habits are of perennial interest to field ornithologists, and constitute much of the charm attached to the outdoor study of birds.

No other British Gull is so much of a land-bird as this one is, and it appears to me that it is becoming greatly more attached to the land in several respects than it was in by-past years. So far as my own experience goes, it was in the abnormally severe winter of 1878–79 that I first noted these Gulls perched in rows upon house-roofs, or alighting on the streets, or coming to the back gardens and such places for food. Previously this habit was only indulged in by an odd bird or two. Since then it has become quite an everyday thing whenever frost of a few days' duration sets in. And there can be little question that they spend far longer time nowadays upon the pasture fields and amongst the crops, instead of going away to the river-sides, estuaries, and shores, as they once did when nesting-days were over. An older generation looked upon the presence of flocks of these Gulls on far inland pastures as presaging storms and unsettled weather. One never hears now of their mention in this connection; rather, their absence would call for comment. Undoubtedly the amount of food—insectivorous and vermiform—they consume the year round, together, of course, with the astounding increase of the Starling within the last thirty-five to forty years, may be set down as the principal factors that have caused the no less astonishing and remarkable change of habits in the Rook, that has so greatly affected the equanimity of game-preservers. The poor Rooks have been deprived of their natural and rightful share, and have been compelled to try elsewhere for a living at their most pressing time of need, in April and May.

The particular purpose of the present paper is to draw attention to the habit of the Black-headed Gull of catching moths. I first watched them do this in the fine hot and dry summer of 1868. For long subsequent to that year they could only be seen capturing moths on the wing during similar warm summers; but for at least the last dozen of years these Gulls have regularly and constantly presented this habit. Either from choice or necessity the catching of Lepidoptera after nightfall has become a confirmed annual practice. Formerly we meet, in ornithological literature, with short and fragmentary allusions to this species feeding on the Ghost Moths, picking these from the grass-stems. There seems every reason to believe that moth-catching by this species began with the Ghost Moth. Accurate observers like Blake-Knox and Robert Gray only name Ghost Moths; if other species were taken they would have been specified. One of the latest present-day notes referring to this habit is in 'British Birds, their Nests and Eggs' (vol. vi. p. 73), where Dr. H.O. Forbes says: "In summer feeds on insects, and especially moths, which it hawks on the wing." That shows how the habit has widened from "Ghost Moths" in particular to "moths" in general.

The habit in question is no mere incidental occurrence confined to a few birds in a restricted locality. It is nightly indulged in by apparently the whole of the birds, and carried on for many a mile around all the breeding colonies in certainly the lowlands of Scotland, south of the Forth and Clyde, and across most of the North of England. Where I have not had personal observation to rely on, I have had the benefit of trustworthy information.

It first becomes widely noticeable as a habit about May 25th, and continues every fine quiet night till about July 20th. After that date, although it does not altogether cease, it appears to be indulged in merely to an individual and rather desultory extent. In the bright gloaming of our northern summer, about the time the last Blackbird lays aside his flute for the night, the Gulls put in a rather sudden appearance, flitting low along the grass, hedgerows, and clumps of shrubs, confining their attentions to such places at first. As the evening wears on they rise higher over the tree-tops and along the woodlands, and for the remainder of the night they frequent these loftier heights, only coming down lower when the night is specially bright, or becomes breezy. So far as I have seen, they take any and every moth they can catch. Early in the evening they can be seen snapping up many easily recognizable species. I have seen them take moths so small as a Depressaria. The Gulls capture the moths most dexterously, and it is curious to notice a Gull occasionally make a rush and chase a Bat, probably getting jealous of its moth-catching rival, or perhaps mistaking the flying insectivore for an insect of more than usual dimensions. Standing beneath a tree, over whose top a Gull is gliding, one hears the chuckle of satisfaction emitted when it catches and swallows a victim. Many of the swift-flying Noctuæ are safe from the Gulls' attentions so long as their usual headlong flight of the early evening continues, but when speed slackens, and they begin to dawdle—as perhaps all the species do in later hours—then the Gulls snap them up continuously.

This moth-catching habit, which has developed so regularly in recent years, occupies, as I have stated, a well-defined period, beginning quite abruptly, and almost to an hour at the same time each season. In various ways, which need not be particularized, I have ascertained with tolerable certainty that throughout the region specified the moths thus caught are for the purpose of feeding the young. No doubt, immature non-breeding birds take part in the pursuit, and apply the proceeds to their own uses, but the main purpose is capture by the breeding birds to feed their young ones.

In this connection I may refer to an excellent paper by Prof. J. Arthur Thomson, M.A., entitled "Some Notes on the Behaviour of Young Gulls artificially hatched and naturally hatched," read at the recent Glasgow meeting of the British Association. I had the pleasure of listening to this paper, which is printed in extenso in the British Association Report for 1901, p. 378. The young Gulls were L. ridibundus. Prof. Thomson says:—"They [the newly-hatched Gulls] pecked at the cotton-wool of their beds" (loc. cit. p. 379); and further on he says again: "During the first two days they got some of the cotton-wool of their beds into their mouths, but this was inevitable" (p. 380). Why "inevitable"? The Professor evidently attributes this to infantile blundering, but may it not be considerably nearer the mark to suggest that it was due to a longing for the dry fluffy moth-food their hereditary instinct told them they should be provided with? I should have made my suggestion when it occurred to me on the spot, but the formidable row of grey beards and bald heads that clustered round the President of Section D was too awe-inspiring to a mere listener on the back benches.

A further but greatly less marked modification of the habits of this species may also be described here. During those rather infrequent bright and very still days we have in September and October, when insects rise high into the air, Jackdaws and Starlings combine to hunt them, gliding backwards and forwards, Swallow-like, for hours at a time. Always within my recollection such gatherings have occasionally included one or two Blackheaded Gulls, but nowadays one never sees them without the Gulls. And the latter may often preponderate in numbers. On such autumn days—days which, it may be said, are invariably characterized by strong migration movements—the principal insect that is being pursued is a large black species of Chironomus.