VOL. vin.] A STUDY OF BIRD CECOLOGY. 187 



or weeks they remain, how much the flock varies from 

 day to day, at what hour of the day they appear, 

 whether they make a round of the fields each day or 

 remain in one place all the time ; what food they seem 

 to prefer, and how far this varies during the season 

 or even during the day ; how far such changes of food 

 are due to shortage of one sort or ripening of another ; 

 we may endeavour to watch the flocks flying to or 

 from their roosting-places, and see whether they fly 

 straight from all points or travel by well-defined routes — 

 or ill-defined routes. Similar observations may be made 

 with regard to Waders on the shore, and to the roving 

 bands of Tits and other little birds in the woods. 



How can such observations be made ? To obtain 

 exact information of the status of each species of bird 

 nesting in any district, and of its comparative 

 number from year to year, I think the mapping system 

 explained by my brother and myself in an early number 

 of British Birds (Vol. II., pp. 322-6) is probably as 

 satisfactory as any. This may easily be done by obtain- 

 ing an ordnance survey map of the district required,, 

 six inches to a mile scale, and placing a symbolical 

 number or mark at any spot where a species is observed 

 (seen or heard) daily during the breeding-season ; this 

 method is admirable for all birds that have a well- 

 defined breeding- range, such as the Chats, Warblers, 

 Wagtails, Pipits, Flycatchers, Buntings, Woodpeckers 

 and other species. But some of the very common 

 birds, such as Blue -Tits, Robins, Thrushes, Blackbirds, 

 and Hedge-Sparrows (I am thinking of the south-east 

 of England), are too numerous for any map short of 

 the twenty-five inch to a mile scale. As regards species 

 which nest in colonies, the most satisfactory method 

 of discovering their number exactly is obtained by 

 counting the nests ; in his Birds of Dumfriesshire^ 

 Mr. H. S. Gladstone gives important results of such 

 observations on Rooks, Herons, and Black-headed 

 Gulls. There remain a number of species which are 



