Some Results of Bird-Lore's Christmas Bird Censuses 13 



not the slightest motion beyond that caused by their breathing, and squatted 

 close to the uncomfortable-looking pebbles. 



However we may criticise the Nighthawk for deserting the pure air of the 

 country for the city's grime and smoke, we must admit, at least, that in the 

 tar-and-gravel roof she has selected about as admirable a background as could 

 be found for the concealment of herself and her offspring. The downy chicks, 

 especially, were practically invisible from a short distance, and they added to 

 the delusion by their motionless crouching. They permitted unlimited time 

 exposure from every angle, till the sun was gone altogether and we were obliged 

 to withdraw from the roof. 



Some Results of Bird-Lore's Christmas Bird Censuses 



By E. H. PERKINS 



THE following curves and diagrams are based on the Christmas Bird 

 Censuses published in Berd-Lore from 1901 to 1911. In the great 

 accimiulation of data in these reports much can be learned on the winter 

 distribution of a given species over a series of years. In the figures given in 

 this article, I have plotted the rise and fall in numbers of ten species of winter 

 birds over an area including New England and New York. The species have 

 been selected from the two classes into which our winter birds fall. From the 

 regular residents I have taken the Chickadee, White-breasted Nuthatch, 

 Downy Woodpecker, and Brown Creeper. The irregular winter visitants are 

 represented by the Red-breasted Nuthatch, Pine Siskin, Redpoll, Pine Gros- 

 beaks, and the Red- and White-winged Crossbills. In plotting the curves, the 

 years are taken as the abscissas, while the ordinates are found by dividing the 

 total number of indixdduals seen each year by the number of reports for that 

 year. In figure II the scale of the ordinance is twice that in Figure I, otherwise 

 the curves of the birds in Figure II would be too flat to show well. The curves 

 start with 1901, as I was unable to obtain the census for 1900. 



There seems to be some evidence that the various species of birds rise and 

 fall together in abundance. This is best seen between 1905 and 1907. The 

 year 1906 was one of abundance for almost all species. This year was 

 preceded and followed by years of general scarcity. About 1903 and 1904, 

 and again in 1908, there seems to have been a more or less general rise in 

 abundance. 



It might be expected that the curves of the regular winter residents would 

 be fairly regular, and that those of the boreal species would be more or less 

 jagged. This expectation is, in every case but one, borne out by the 

 facts. The exception is the Chickadee. This bird is an abundant permanent 

 resident over the area under consideration, and a regular curve might be 

 expected. The fact is that the Chickadee shows one of the most irregular of all 



