32 



NATURALIST'S GUIDE TO THE AMERICAS 



or refuge, the list is found to be rela- 

 tively short, especially if the locality is 

 distant from a river or lake. From 

 several locality lists available to the 

 writer, each including from 85 to 170 

 species, it is evident that about 75 per 

 cent of the species listed are in one way 

 or another dependent on trees or shrubs. 

 Since, of course, the same ratio may not 

 hold for the number of individual birds 

 found, it is desirable to ascertain, if 

 possible, what share of the bird popula- 

 tion of an average Illinois locality is 

 independent in every way of trees and 

 shrubs. Fortunately a pretty close ap- 

 proximation to such knowledge is ob- 

 tainable from the very extensive and 

 useful data accumulated by Prof. S. A. 

 Forbes from the work of expert ornitho- 

 logical assistants in 1906, 1907 and 1909. 

 Two such observers, traveling in 

 straight lines and always 30 yards 

 apart, recorded all the birds flushed on 

 a strip of land 50 yards wide and those 

 that crossed the strip within 100 yards 

 ahead. They recorded also the char- 

 acter of the fields traversed and the 

 distances in each. Heavy timber in 

 which there was little chance of a com- 

 plete count was disregarded/and the 

 record was, of course, deficient for water 

 birds. This work was carried on during 

 all seasons of the year and was nearly 

 equally distributed between the north- 

 ern, central and southern parts of the 

 state. The results show the numbers 

 and kinds of birds in samples of the 

 various sorts of environment in the 

 state, equivalent to a strip of land fifty 

 yards wide and over two thousand miles 

 long. Among these results we have 

 record of 48,558 birds from 39,940 acres. 

 There were 9199 English sparrows and 

 546 birds were not positively identified. 

 Deducting these latter two classes, we 

 have record of the identity of 38,813 wild 

 birds as distributed over farm lands, 

 orchards, and shrubby areas and open 

 woodlands. One hundred and seventy 

 species were represented, 44 of which 

 may be regarded as independent of 

 trees and shrubs able, apparently, to 

 get along perfectly well without them. 



Of these latter 24 species are birds of the 

 open field and the others are shore birds 

 or water birds. Of the remaining 126 

 species many will eventually disappear 

 altogether, and the others will be rep- 

 resented in reduced numbers in locali- 

 ties where trees and shrubs are de- 

 stroyed. About 69 per cent of the 

 individual wild birds recorded by the 

 foregoing observers belong to this group. 

 These ratios correspond very closely 

 with those from other available records 

 based on more limited data. Fully two- 

 thirds of the wild birds of ordinary 

 Illinois localities are in some way de- 

 pendent on trees and shrubbery. The 

 reasons for this dependence differ 

 greatly for various species. Many, in- 

 cluding some of the woodpeckers, are 

 wholly dependent on trees for food, 

 nesting sites and places of refuge. In 

 most cases the insects associated with 

 the trees supply the food, although to 

 some extent the seeds, buds and even 

 the cambium layer (in case of trees 

 visited by the yellow-bellied sapsucker) 

 may be eaten. Numerous other species, 

 while getting their food from the ground 

 or from the flying insects of the air, 

 depend on trees or shrubbery for nesting 

 sites or refuge or for lookout stations. 

 Here, again, there is great diversity, 

 since some kinds frequent mostly the 

 upper parts of the trees, others prefer 

 the lower parts, while still others are 

 limited to those woods in which the 

 ground is more or less covered with a 

 thick undergrowth. Comparatively few 

 species prefer the interior of the heavy 

 forest, but many more frequent the 

 forest margins or open woodlands, es- 

 pecially those with thickets. Shrubby 

 fields and hedges are preferred by a 

 number of species. 



A large majority of the birds that pass 

 the winter with us and of those that 

 come from the south in the early part 

 of the spring migration are of the 

 thicket-and shrubbery-loving kinds. To 

 find them we must seek them in the 

 environment they prefer along hedges, 

 in neglected berry patches, in shrubby 

 pastures, or in woods with plenty of 



