REPORT ON BITID CENSUSES, 1916-1920. 21 



in number: pos8i>)ly overstocking the range with cattle, sheep, and goats had some- 

 thing to do wath it, and the long drought of a few years ago helped to diminish their 

 numbers. I think it quite possu^le that they migrated in search of better conditions, 

 and I don't think, as some people here do, that they just died out. 



Raton, N. Mex. — A bird census on a tract of 160 acres near Raton, 

 N. Mex., at an altitude of about 6,500 feet, was taken in 1916 and 

 repeated in 1920. This land is prairie, and the nearest timber is 3 

 miles away. A small creek in which there is water throughout the 

 year crosses the tract, and the crops are all irrigated. In 1916, 12 

 acres, or 7 per cent of this tract, were under cultivation, and 78 pairs 

 of birds representing 13 species were found breeding. In 1920, 

 with 50 acres, or 31 per cent of the land, in crops, the number of 

 birds was 97 pairs of 12 species. Here the bird life has increased as 

 more land is put under cultivation, while in the more humid sections 

 of the country the reverse is usually the case. Additional food 

 supply due to the raising of more grain may have been the chief 

 factor in this increase in the bird population, since in 1920 there was 

 a colony of 20 pairs of cliff swallows, while in 1916 none of that 

 species was present. This species feeds extensively on the insect 

 enemies of grain and alfalfa that had doubtless multiplied with the 

 increased acreage in these crops. 



RELATIVE ABUNDANCE OF CERTAIN SPECIES. 



The study of the density of bird life has not been continued long 

 enough, nor have bird counts been made on a sufficiently large scale, 

 to learn definitely the relative abundance and distribution of indi- 

 vidual species. To see what could be learned even from the data 

 available, the following 10 widely distributed species of native birds 

 were selected for special study: Bluebird, robin, house wren, brown 

 thrasher, catbird, song sparrow, chipping sparrow, meadowlark, 

 kingbird, and flicker; with these were included the English sparrow 

 and European starling, the latter still being confined to the North- 

 eastern States throughout the period covered by this report. Inter- 

 esting but by no means final results were obtained, and the returns 

 of another five years may completely overthrow them. 



The accompanying table (Table 7), dealing with six of the most 

 abundant species in the Northeastern and North Central States, 

 shows for each, on the basis of the returns, its percentage of the whole 

 number of birds reported, and the average nimaber of breeding pairs 

 per hundred acres. In figuring the number of pairs of birds per 100 

 acres, the nearest whole number has been used and a plus or minus 

 sign affixed. This table should be studied in conjunction with that 

 showing the character of land on w^hich the counts were made (see 

 Table 1, p. 8), since there is a direct connection between the kind 

 of land, crops, etc., and the species and number of birds breeding. 



