SEED AND FRUIT COACTIONS 127 



opening of the cones. After trees again begin bearing and the ani- 

 mals return, the cones are so completely harvested that seedlings 

 rarely appear, even where space and germination conditions are 

 favorable. 



Seasonal Coactions in Birds. This group includes the vast majority 

 of gallinaceous and passerine birds, the species and individuals con- 

 cerned being very numerous. In the large forms such as wild turkeys, 

 pheasants, and quail, a scratching reaction on litter and leaf mold is 

 similar to the rooting of peccaries and swine, turning up fruits, seeds, 

 nuts, and invertebrates. The diet of the bobwhite has been studied 

 much more thoroughly than that of other members of the group, espe- 

 cially by Handley (Stoddard, 1931) and by Judd (1905). The food of 

 chicks was found to consist of 84 per cent of animal matter, by con- 

 trast with 22 per cent for adults; the two largest items were beetles 

 38 per cent and grasshoppers 27 per cent. For adults, the plant and 

 animal material, and the major items in each, fluctuated greatly dur- 

 ing the year. The maximum for the plant material occurred in Janu- 

 ary and February with 98 per cent, contrasting with 2 per cent for 

 animals, but the animal material rose to 38 per cent in October, leav- 

 ing 62 per cent for plants. In nature even these larger birds rarely if 

 ever bring about denudation other than in minute areas, but they may 

 affect composition and invasion directly through eating or disseminat- 

 ing seeds and fruits. 



Perching Birds. The food coactions of this vast group may be 

 exemplified by the following tables. These have been compiled from 

 several sources, chiefly Forbes, jMcAtee, Henshaw, Beal, and Gabriel- 

 son; although the values are more or less typical, they cannot take 

 account of all regional, annual, and individual variations. 



The fruit- and seed-eating birds do much under agricultural condi- 

 tions to plant certain shrubs and trees. The prevalence of sumac, 

 trumpet vine, mulberry, etc., along fences is evidence of their work. 

 One of the best demonstrations of the effect of this group of birds on 

 the composition of communities resulted from the controversy as to 

 whether trees would grow on prairie soil. In 1875 and at various 

 subsequent dates, some 18 acres of prairie soil on the campus of the 

 University of Illinois were set with trees of about 30 species. Many of 

 these died, and frequent cutting of the undergrowth largely prevented 

 the development of the forest which would have succeeded. However, 

 under a grove of green ash the recurrence of seedlings was striking, 

 especially of cherry, hackberry, sassafras, grape, Virginia creeper, cur- 

 rant, and other shrubs with fruits having indigestible pits, indicating 

 that the succeeding forest would have been planted by birds. 



