June 12, 1908] 



SCIENCE 



919 



The method of the enumeration was such 

 as to give the numbers of each species 

 found on measured areas, taken at random, 

 of each crop or other distinguishable kind 

 of surface. The responsible observer, Mr. 

 A. 0. Gross, determined 7,740 birds be- 

 longing to 85 species — an average of 645 

 birds to the square mile, of which 18 per 

 cent, were English sparrows. On this 

 basis, the total summer population of the 

 state numbers about 30,750,000 birds, of 

 which five and a half millions were English 

 spari-ows. Eighty-five per cent, of these 

 birds belonged to one fourth of the 

 species. The ten most abundant species, 

 and the numbers seen of each, were as 

 follows: English sparrow, 1,414; meadow- 

 lark, 1,025; bronzed grackle, 900; mourn- 

 ing-dove, 461; dickeissel, 393; red- winged 

 blackbird, 347; prairie horned lark, 296; 

 flicker, 197 ; robin, 194 ; and field sparrow, 

 186. 



The English sparrows decreased in num- 

 bers per square mile from north to south 

 (perhaps because of a diminishing popula- 

 tion southward and a consequent progress- 

 ive diminution of their breeding areas), 

 100 sparrows in northern Illinois being 

 represented by 77 in central and 56 in 

 southern; but the native birds increased 

 from north to south, apparently for cli- 

 matic reasons — 100 in northern Illinois 

 being represented by 116 in central and 

 129 in southern. The same gradation was 

 still more pronounced in winter residents, 

 which averaged 384 birds to the square 

 mile in northern, 582 in central and 832 

 in southern, Illinois. The general average 

 for the whole state and the entire year, as 

 represented by 1,591 miles of travel and a 

 census area of 44J square miles, was 722 

 l)irds to the square mile. 



By comparison of the midsummer num- 

 bers with the average for the fall migra- 

 tion period, a wave of denser population 

 was detected, running from north to south 



and rising with the progress of the migra- 

 tion. The central Illinois average for Oc- 

 tober was 2.3 times that for July, August 

 and early September. 



The original relation of the Illinois bird 

 fauna to prairies was still discernible in 

 the fact that half of these summer birds 

 were found in pastures and meadows, 

 although only a little over a third of the 

 area inspected was in grass. Corn fields, 

 on the other hand, which covered 32 per 

 cent, of the area, contained but 15 per cent, 

 of the birds, and these most largely Eng- 

 lish sparrows. 



As an example of the local and numer- 

 ical distribution of species, that of the 

 meadow-lark was given, and as an example 

 of the composition of the bird fauna 

 of an ecological situation, the birds of 

 the pasture were separately discussed. 

 Meadow-larks, while numbering 85 to the 

 square mile for the whole area covered, 

 were very unequally distributed, averag- 

 ing 266 to the square mile in fields of 

 stubble, 205 in meadows, 144 in pastures, 

 and 10 in corn fields, and not occurring at 

 all in forests or among shrubbery. They 

 increased notably in number from north to 

 south— 100 in northern Illinois being rep- 

 resented by 175 in central and 215 in 

 southern. 



Pasture lands were the preferred resort 

 of the most abundant midsummer species, 

 and contained 27 per cent, of all the birds 

 seen. In average density of population, 

 however, they were surpassed by meadows, 

 which contained 920 for each square mile, 

 to 878 in pastures, 562 in stubble and 

 small grain, and 300 in fields of corn. 

 The commonest pasture birds were the 

 English sparrow, the crow-blackbird, the 

 meadow-lark, the horned lark, and the field 

 sparrow, abundant in the order named, and 

 together making more than half the sum- 

 mer residents of the pasture lands of the 

 state. 



