306 



through the food relation that birds affect the welfare of other 

 animals and of plants. These studies, although both qualita- 

 tive and quantitative as related to the welfare of the various 

 species of birds themselves, have been qualitative only as con- 

 cerning the relation of birds to the general welfare; and we 

 have little but vague estimate and doubtful surmise in place 

 of a definite knowledge of the relative ecological values of the 

 various species, and equally little knowledge, in consequence, 

 of the total significance of birds as a class. We do know fairly 

 well (owing, in part, to the early work of this Laboratory*, but 

 mainly to that of the United States Biological Survey) the 

 principal features of the food of many species of our common 

 birds, but we can not lay these data together for an intelligent 

 estimate of the total effect of the life of ))irds on their environ- 

 ment except on the supposition that the various species are 

 about equally abundant wherever they occur. That this is not 

 the fact is obvious to every one, and it must be equally obvious, 

 consequently, that until we know how abundant, on an aver- 

 age, the various species are in the various parts of the country 

 and .throughout the country at large, we can make little def- 

 inite application, either .scientific or strictly practical, of the 

 knowledge we now have. Our present information in this field 

 is like a chain one of the links of which is missing and has 

 been replaced by a piece of twine. To substitute iron for cot- 

 ton at this point is the object of the studies now in progress in 

 Illinois on the local distribution, average numbers, and ecolog- 

 ical preferences of the various species of Illinois birds. 



The Field Method. 



To this end, after a preliminary quantitative study made 

 in 1905-06 of the bird life of a single limited tract — a 400-acre 

 stock and grain farm in central Illinois — a systematic program 

 of field observation and statistical record was entered upon last 

 August, with complete arrangements for its continuance 

 through one entire year. Two acute and thoroughly reliable 

 ornithological observers — one of whom, Mr. A. 0. Gross, al- 



* See Bull. 111. State Lab. Nat. Hiat, Nos. 3 and 6, Vol. I. 



