5IO 



NATURE 



[January 7, 19 15 



and of our fisheries, that such work is more and 

 rnore becoming a necessity and one also fraught 

 with great possibihties. So clearly has this been 

 recognised by other countries that special State 

 officers devote the whole of their time to the 

 elucidation of the various problems in connection 

 with economic ornithology. If a particular species 

 confers greater benefits than injuries, and we are 

 not affording it all the protection possible, we are 

 pursuing a downgrade and very dangerous course, 

 which cannot fail but produce direct injury to 

 the State. 



The subject is a complex one, approachable 

 from many sides, and any investigations, to be 

 of real value, must entail a large amount of 

 careful and detailed work extending over some 

 considerable period of time. The mere cata- 

 loguing of the crop or stomach contents of a 

 limited number of specimens of any species, ob- 

 tained at a particular period from one locality is 

 really of very little value. As the writer has else- 

 where stated,^ " In order to arrive at a proper 

 understanding of the food of any particular 

 species, it is necessary to examine the food con- 

 tents found in the intestinal tract during the 

 different seasons di the year and from various 

 districts. Further, careful observations must be 

 made in the field, and of the nature of the food 

 brought to the nest by the parents during the 

 breeding season, and also of the faecal contents 

 extruded from the nest." 



We now know that many of the earlier records 

 are either only partially correct or will scarcely 

 bear the interpretation put upon them by their 

 respective authors, for two most important factors 

 have been overlooked, viz., the rate of digestion, 

 and the intestinal food contents found beyond the 

 region of the gizzard. The rate of digestion, 

 according to experiments at present in hand, 

 would seem to vary in different groups of birds ; 

 as yet but little work has been done in this in- 

 teresting field, a more accurate knowledge of 

 which must largely alter our ideas of the various 

 statistical tables which have been given for 

 different species. 



Under certain conditions, e.^. , during dry 

 summers,^ a much larger percentage of weed 

 seeds pass through the intestinal canal uninjured, 

 due to the fact that under such climatic conditions 

 a much smaller percentage of grit and soil is 

 taken into the intestinal canal. Thus, observations 

 made upon the grit and soil content in the gizzard 

 of thirty-six rooks during the dry summer of 191 1 

 (June to September) showed that the average con- 

 tent was 108 grains, of which not more than one- 

 sixth was grit, whereas in the same number of 

 birds examined during the wet summer of 1912', 

 the average amount was 214 grains, of which 

 nearly one-third was grit. Similar investigations 

 carried out on the starling and house-sparrow 

 gave an average, in 191 1, of 42 and 27I grains 

 respectively, as against 68 and 53 grains in 1912. 



In the past it has been all too readily assumed 



1 " The Food of Some British Wild Birds," 1913, p. 7. 



2 Journ. Econ. Biology, 1914, vol. ix., p. 69. 



NO. 2358, VOL. 94] 



! that those species that feed upon insects and upon 

 ! weed seeds must be beneficial. We now know 

 that no hard and fast line can be drawn : much 

 I careful and extended work is necessary on each 

 j individual species before it can be definitely stated 

 that a species is injurious or beneficial. 



To the farmer and fruit grower such information 

 I is of the greatest import, for at the present 

 moment they suffer enormous annual losses due 

 to certain species of birds. 

 i Of the majority of species of British wild birds, 

 it is generally agreed that they are beneficial, of 

 the remainder the present writer has elsewhere 

 stated that : " Many species which are injurious 

 at one season of the year are distinctly beneficial 

 for the remainder. Again, many birds that are 

 beneficial, may, if allowed unduly to increase, 

 become equally injurious. In other cases the 

 partial failure of their natural food supply, or 

 other causes, may lead to a change in their food 

 habits, in a like manner, the alteration or removal 

 of their natui'al environment m.ay lead to equally 

 disastrous results." 



Although in some districts farmers and others 

 are loud in their complaints of the injuries in- 

 flicted, any policy of wholesale destruction would, 

 we believe, be equally disastrous. In nearly all 

 cases, "the misdeeds of birds are much more 

 manifest than the benefits they confer upon us." 

 With the exception of doves and pigeons, 

 practically all birds feed their young upon an 

 animal diet, whatever the nature of the food of 

 the adult may be, and the bulk of the food con- 

 sists of insects. These are destroyed just when 

 they are capable of inflicting the greatest possible 

 harm upon our crops and orchards. Further, 

 during the nestling season, the young birds re- 

 quire an enormous amount of food ; feeding 

 commences before sunrise and continues after 

 sunset. The starling is known to pay nearly 200 

 visits to the nest a day, and in the case of the 

 house-sparrow, between 220 and 260 visits daily 

 have been counted. In any attempt, therefore, 

 to estimate the value or economic status of a 

 species, the nature of the food of the nestlings 

 must be taken into consideration. 



A careful investigation extending over a period 

 of ten years, entailing an examination of the 

 stomach contents of upwards of 4000 adult birds 

 and 600 nestlings, and numerous observations in 

 the field and laboratory shows that we can classify 

 the commoner species under five headings, viz. : — 



1. Distinctly injurious. — House-sparrow, bull- 

 finch, sparrow-hawk, wood-pigeon, and stock- 

 dove. 



2. Too plentiful, and consequently injurious. — 

 Missel thrush, blackbird, greenfinch, chaffinch, 

 starling, and rook. 



3. Injurious, but not plentiful. — Blackcap. 



4. Neutral. — Jay. 



5. Beneficial. — Song thrush, fieldfare, white- 

 throat, great tit, blue tit, wren, goldfinch, linnet, 

 yellow bunting, magpie, jackdaw, skylark, barn 

 owl, brown owl, kestrel, and plover. 



The so-called "avian rat," the ubiquitous house 



