REPORT ON BIRD CENSUSES, 1916-1920. 33 



which H are in orchard, 4 to 5 in crops, and none in woods, there 

 was an average population for four years of 32 species and 121 pairs 

 of native birds and 2 pairs of English sparrows. 



SUMMARY. 



Results of bird censuses for the five years 1916 to 1920, inclusive, 

 show a very close agreement with those obtained in 1914 and 1915 

 for the section of the country lying north of Maryland and the Ohio 

 River and east of the Great Plains — a little more than one pair of 

 birds to the acre as the average for farm land. For the land iiyime- 

 diately surrounding the buildings and including the lawns and orchard, 

 on the average about 130 pairs of birds are found to nest on 100 acres; 

 the estimated bird population of the entire farm is about 112 pairs 

 to 100 acres. 



The counts made in the southeastern section of the country have 

 been on tracts so scattered and of so small an acreage that no con- 

 clusions concerning the average bird population are yet possible. 

 The same is true of counts on the Plains, where, except for a few 

 species, birds are largely confined to river bottoms and planted 

 groves. In the Rocky Mountain region and westward, the country 

 is even more diversified, and the added problem of altitude makes 

 general averages practically impossible, even with many times the 

 data now at hand. 



The robin is the most abundant species in the States north of 

 North Carolina and east of the Mississippi, and the English sparrow 

 is second. For the farm land in this section, as represented by the 

 counts, there are approximately 9 pairs of robins and 8 pairs of 

 English sparrows to 100 acres. 



No general statement of the average bird population of marsh 

 areas is at present possible. The marshes are the home of several 

 colony-nesting species, and the population per acre is, therefore, 

 usually much greater than on farm land. 



In small patches of woodland, especially when they are surrounded 

 by cultivated fields, birds nest very abundantly, but in the deeper 

 woods they are scarce. For the former, the average bird population 

 is 182 pairs to 100 acres; but the estimate given of 68 pairs to 100 

 acres of the latter is probably rather high. Several counts made in 

 the forests of the Rocky Mountain region show about one pair of 

 birds breeding on two acres, and it is probable that the same propor- 

 tion holds in similar regions in the Eastern States. 



The counts of 1918 showed birds to be much less abundant than in 

 other years covered. Unfavorable weather conditions during May 

 and June of the year preceding took heavy toll of the insectivorous 

 birds throughout the States east of the one hundredth meridian, and 

 unusual storms in the Southern States during the winter and spring 

 which followed proved hard on birds wintering there. By 1920 much 

 of the loss had been regained. 



Birds respond to protection, and on areas where they are protected 

 they nest much more abundantly than on surrounding territory. 



