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NATURE 



[April 8, 1920 



Sea-birds: Their Relation to the Fisheries and Agriculture. 

 By Dr. Walter E. Collinge. 



P\ URING the past few years there has been 

 ^^ a growing opinion on the part of the general 

 public and those connected with our fisheries that 

 the enormous number of sea-birds on our coasts 

 are inimical to the fisheries and to a less extent 

 to agriculture. This view has been fostered to 

 a large degree by the public expression of 

 irresponsible statements and by the fact that we 

 do not possess any exact and trustworthy know- 

 ledge of the nature of the food of these birds. 

 Even amongst ornithologists and other students 

 of wild-bird life widely divergent views are held. 



Hitherto no investigation suflficiently compre- 

 hensive has been made, and in those cases where 

 the birds of a restricted area have been studied, 

 or where an insufficient number of specimens has 

 been examined, the results have proved incon- 

 clusive, and, owing to the methods employed, to 

 some extent misleading. 



About two and a half years ago, under the 

 auspices of the Carnegie Trust for the Universities 

 of Scotland, an investigation was commenced in 

 which it was proposed to examine large series of 

 each species from numerous localities during 

 each month of the year, and to estimate the food 

 by the volumetric method. Although this research 

 is not yet complete, sufficient data are in hand to 

 warrant an expression of opinion upon this 

 subject, and it is felt that such is highly desirable 

 at the present time, when so many erroneous 

 views are being circulated. 



Up to the present, fourteen species have been 

 examined, represented by upwards of three thou- 

 sand specimens. The species are cormorant, 

 shag, common gull, herring gull, great black- 

 backed gull, lesser black-backed gull, black- 

 headed gull, kittiwake, common tern, razorbill, 

 guillemot, little auk, puffin, and great northern 

 diver. Whilst it is not possible here to reproduce 

 the numerous percentage tables showing the 

 nature of the food for each species during the 

 various months of the year, or those illustrating 

 the seasonal variations or the percentages of the 

 different species of fish destroyed, it is possible 

 to make a general statement which we believe 

 future work will more fully amplify and confirm. 



First, we would point out that the importance 

 and amount of fish that has been generally 

 regarded as forming the diet of most of these 

 birds are not borne out by an actual examination 

 of their crop and stomach contents. Fish does 

 not (with such exceptions mentioned later) con- 

 stitute the bulk of their food or anything like the 

 major portion of it. Indeed, one has only to watch 

 carefully such species as the black-backed gull, the 

 herring gull, and the lesser black-backed gull on 

 the shore after the ebb of the tide to realise how 

 essentially these birds are the scavengers of the 

 shore. If they turn landwards, then injurious 

 insects, earthworms, frogs, and carrion are 

 greedily fed upon. Further, if one confines one's 

 NO. 2632, VOL. 105] 



observations to birds drowned in the fishermen's 

 nets, entirely misleading ideas are obtained, for 

 these few birds constitute but the merest fraction 

 of the huge bird population frequenting our coasts. 



The above-mentioned fourteen species may be 

 divided into three classes, viz. : (i) Purely fish 

 feeders ; (ii) largely fish feeders, but most of the 

 fish are not utilised by man as food ; (iii) fish 

 feeders to less than 20 per cent, of the total bulk 

 of their food. Most of the species fall into 

 class (iii). In class (i) is placed the cormorant 

 and shag, for, so far as observations go, their 

 food consists entirely of fish, and chiefly of food 

 fishes. In class (ii) is placed the common tern. 

 The remaining eleven species must all be placed 

 in class (iii). 



From information obtained from various 

 sources, there is a general consensus of opinion 

 that the cormorant and the shag do an enormous 

 amount of harm to the fisheries. Nothing can be 

 advanced in their favour, though it is open to 

 question whether our fish supply would show any 

 increase even were these birds exterminated. 

 Respecting the common tern, sand eels constitute 

 fully 50 per cent, of its fish diet; the gunnel or 

 butter fish, gobies, young gurnard, herring, and 

 haddock are also taken. 



It is not possible here to give the details of 

 the analyses for all the remaining species ; we 

 shall therefore select one, the black-headed gull. 

 More than five hundred specimens of this species 

 have been examined, obtained from various 

 localities and during each month of the year. 

 This species is selected because it has increased 

 enormously during the last twenty years, and is 

 now generally regarded as one of the most 

 injurious both to the fisheries and to agriculture. 



Of the total bulk of food consumed in a year. 

 96 per cent, consists of animal matter, and 4 per 

 cent, of vegetable matter. Of the former the 

 actual amount of food fishes found was 11-5 per 

 cent., and of other fishes (not utilised by man as 

 food) 9 per cent., or a total fish diet of 205 per 

 cent. Edible Crustacea are present to the extent 

 of 4 per cent., and other forms, non-edible, to 

 that of 10 per cent. Marine worms constitute 

 185 per cent., molluscs 4 per cent., echinoderms 

 2-5 per cent., injurious insects 22 per cent., other 

 insects 1-5 per cent., earthworms 10 per cent., and 

 miscellaneous animal matter 3 per cent. Of the 

 vegetable matter, 25 per cent, consists of cereals, 

 and 1-5 per cent, of miscellaneous matter (Fig. i). 



If the huge bulk of food from which these 

 figures have been obtained means anything at all, 

 it indicates clearly and definitely that this species 

 IS a highly beneficial one. By no reasonable deduc- 

 tion can it be shown to be otherwise, for nearly 

 two-thirds of its food is of a neutral nature, viz. 

 60 per cent. (38 per cent, of which consists of 

 shore refuse.) Only 18 per cent, is injurious, 

 and 22 per cent, is highly beneficial. We 



