184 



Illinois Natlrai. History Slrvlv Hui.letin 



Vol. 27, Art. 2 



The collection designed to illustrate the food 

 of birds has been more than doubled in the 

 last two years, and now numbers over six 

 thousand stomachs, representing about two 

 hundre<l species. Kight hundred and eighty of 

 these have now been exhaustively studied, . . . 



L'nf(irtiinatcl\ . the anal\ses were ap- 

 parently discontinued at this point, for 

 there were no more publications on the 

 food of birds, and the annual reports of 

 the State Laboratory of Natural History 

 indicate that nothing further on this sub- 

 ject was done. 



Forbes' evaluations of his findings on 

 the food of birds indicated awareness of 

 the need for giving special consideration 

 to the high niobilit\' of birds, food prefer- 

 ences, density effects, ability to diversify 

 diet, and the importance of seasons, geo- 

 graphic location, and specific ecological 

 circumstances. Fcjrbes ( 1880^' : 122-3) de- 

 scribed what appears to have been a new 

 method of evaluating proportions of food 

 in the stomachs and crops of birds, a 

 technique which is used yet today. He 

 (Forbes 188]r/:107) also showed himself 

 to be aware of the importance of sample 

 size and made crude tests for significance 

 by comparing the results of analyses of 

 small samples with those of larger 

 samples to determine whether there were 

 important departures in the pattern of 

 the diet. 



Because l-'orbes believed that the num- 

 bers and kinds of birds in specific habitat 

 categories needed to be known before 

 their economic importance could be evalu- 

 ated, he encouraged studies based on sys- 

 tematic censuses, which were carried out 

 in 1906, 1907, 1908, and 1909. These 

 studies are classics in American ornithol- 

 ogy and introduce a new censusing tech- 

 nique for birds. I believe them to be the 

 first extensive statistical analyses of bird 

 populations in this country. Although the 

 results of these surveys are presented in 

 six papers, two of them contain most of 

 the data (Forbes & Gross 1922, 1923). 

 Unfortunatrh-, a final paper in which it 

 was hoped to present all of the findings 

 for each species was never published. 

 Plans for this paner are described (Forbes 

 &: Gross 1923:397) as follows: 



It has been our general plan to work at first 

 with broad strokes of the full brush, refining 

 upon our neutral background by degrees and 

 ending, as we hope to do in a pajicr follow- 



ing the pres^ent one, with the final details for 

 each species taken up separately and followed 

 all over the state and aroimd the year. 



Forbes' experience with plankton sur- 

 veys guided him in the development of 

 the census technique devised specifically 

 for the bird surveys (Forbes & Gross 

 1921:1). Forbes believed that two men 

 walking abreast could identify and count 

 all of the birds flushed by them or cross- 

 ing their track on a strip 150 feet wide 

 in relatively open country but 60 feet 

 wide in heavier cover, such as orchards, 

 open woods, and patches of close shrub- 

 bery. This census technique was pictured 

 (Forbes c^ Gross 1921:1) as a 



huge net a hundred and fifty feet wide, 

 drawn in straight lines across every kind of 

 crop or other surface vegetation, by which 

 all the birds found there should be caught 

 and held until they had been identified and 

 counted. 



Results were obtained by application of 

 this census technique during the summers 

 of 1907 and 1909 (Forbes ^' Gross 

 1922:189, 199): the census indicated 

 an average of 852 birds per square mile 

 for the state as a whole. The numbers of 

 birds per square mile showed a striking 

 increase of 54 per cent from the 1907 fig- 

 ure to that of 1909. Orchards were found 

 to have the greatest numbers of birds per 

 square mile, 3,943 ; yards and gardens 

 were a close second with 3,418. The state- 

 wide number of birds per square mile in 

 winter was estimated from data collected 

 in 1906 and 1907 to have been 520 

 (Forbes & Gross 1923:398). 



Dr. Frank Smith (1930) prepared a 

 thorough and useful paper dealing with a 

 chronology of the spring migration of 221 

 species of birds through Urbana from 

 1903 through 1922. The objective of the 

 study was to determine whether there was 

 a correlation between migration flights of 

 spring migrants and certain kinds of 

 weather. Smith (1930:112) concluded: 



.\ careful study of the weather maps during 

 the time when recorcis were being made re- 

 vealed that the greatest migratory activity 

 in spring occurred at times when the weather 

 maps showed an area of low barometric 

 pressure approaching from the west, with the 

 south w'inds and rising temperatures which 

 normally accompany such movements. 



The monograph by Dr. Alfred O. 

 Gross (1921) on the dickcisscl must be 



