514 



THE AMERICAN NATURALIST [Vol. XLII 



total acreage in these lands was but 36 per cent, of the 

 entire area inspected. These figures are equivalent to a 

 density ratio on pastures and meadows of 1.39 for all the 

 birds of the state. 5 Corn is an exotic crop in Illinois, 

 and birds were only about a third as abundant in corn 

 fields as in grass lands, while in small grains they were 

 nearly twice as abundant as in corn. The acreage in 

 these crops was such that 15 per cent, of all the birds of 

 the season were found in corn fields and 22 per cent, were 

 in small grain. In orchards they averaged 4^ times as 

 numerous to the unit of area as in fields of grain, 2,471 

 to the square mile— giving a density ratio of 3.84; but the 

 acreage in orchards from which the birds were identified 

 was so small that all the orchard birds together amount 

 to only 2 per cent, of the whole number observed. Among 

 native trees and shrubbery, birds were much less abun- 

 dant than among fruit trees, and the density ratio for 

 these situations was about 2.25. 



By way of further illustration of the application of this 

 quantitative method to the subject of local distribution, I 

 will present some of the more pronounced results for one 

 species of bird throughout its range in summer, and for 

 one kind of crop area as visited or inhabited by mid- 

 summer birds. 



The Meadow-lark 

 One thousand and twenty-five meadow-larks were iden- 

 tified by my observers in their work on the summer resi- 

 dents of the state, an average of 85 to the square mile 

 for the whole area traversed by them. As these birds 

 were unequally distributed, never occurring, for example, 

 in woodlands or among shrubbery, their numbers rose in 

 some situations far above this general average, amount- 

 ing to 266 to the square mile in stubble, 205 in meadows, 

 160 on untilled lands, 143.5 in pastures, and 131 on waste 

 lands, and falling to 10 to the square mile in fields of 

 corn. 



• That is, taking an average density of the bird population for the whole 

 area of the state as 1, the density in pastures and meadows only is 1.3ft 



