SEED AND FRUIT COACTIONS 129 



Scansorial Life Habit. This group comprises those woodpeckers 

 that feed chiefly upon plant materials. However, in spite of the 

 marked structural adaptations of this family, its food habits are fairly 

 generalized, and most of the species are to be regarded as bivores. 

 The most sharply differentiated are the three species of Sphyrapicus, 

 the sapsuckers, which have adapted themselves to a diet of sap and 

 cambium, supplemented in considerable degree by fruits and ants. In 

 Colaptes, the gilded flicker seems to be largely vegetarian, favoring 

 the fruits of cacti; the red-shafted lives on a diet about half ants and 

 half fruits and nuts, while the northern flicker prefers ants to fruits. 

 The red-headed woodpecker mixes plant and animal materials in a 

 ratio of about two to one, but offsets this by a fondness for eggs and 

 nestlings. The California and Lewis woodpeckers prefer acorns, and 

 the former in particular stores these in single caches in the trunks 

 of oaks and pines (cf. Weiss, 1909; Griscom, 1923; Burrt, 1929; 

 Chrysler, 1930). 



The enormous number of acorns taken by certain species suggests 

 that woodpeckers have some effect upon the reproduction of oaks, but 

 of this there is no definite evidence. However, the sapsuckers not only 

 affect the health of trees and deface them by the production of burls 

 and adventitious buds, but likewise injure some of them, especially 

 young individuals, to the extent that they die. IMcAtee (1911) has 

 listed 267 species of trees and shrubs attacked by the yellow-bellied 

 sapsucker. 



Dissemination by Animals. In addition to the distribution of 

 fruits and seeds by animals in the course of food coactions, a number 

 of modifications are concerned with wholly unintentional dissemina- 

 tion. There are four types of these, namely, hooks, spines, awns, and 

 viscid excretions. The first are by far the most numerous and im- 

 portant, hooks and barbs of various form occurring in families as far 

 apart as the peas, parsleys, asters, borages, and mints, as illustrated 

 by the familiar sticktights, beggar's ticks, cockleburs, etc. Spines on 

 fruits are fairly common, but only a few are sufficiently stout to 

 bring about attachment, the best known being the sandbur and the 

 caltrop. The spiny heads of thistles are sometimes caught by the 

 hair of animals, as are the fruits of some cacti, but the most effective 

 distribution of the latter is through the food coaction, the fruits and 

 upper joints of cylindric opuntias especially becoming attached to the 

 jowls of cattle and thus spread about locally. Stipa and Erodium are 

 examples of distribution by means of a sharp callus, and Stipa, 

 Aristida, Bromus, Hordeum, and many other grasses of dispersal by 

 virtue of awns. The use of sticky substances is quite exceptional, and 



