136 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



fied Ijy the characteristic flocking ^ of birds to the scene of insect out- 

 breaks or of other occurrences of unusual abundance of food. 



Constant seeking of the available leads to a wide distribution of 

 predatory attack because of seasonally or otherwise variable abundance 

 or availability of many of the food organisms, further on account of 

 the greater or lesser restriction of predators to specific habitats in 

 each of which the range of food items is diiTerent, and because of the 

 specialization of various predators in methods of seeking food. 



That the predatory attacks of birds are amazingly distributed over 

 the entire animal kingdom, preceding pages bear witness. If it be 

 asked whether birds eat bats or moles, flyingfishes or hermit crabs, 

 dragonflies or mole crickets, sea-urchins or bryozoans, the answer is 

 ever in the affirmative. Given an animal group comprising only a 

 small number of species we find that there are only a few records of 

 birds preying upon it. Given one of large numbers of species we 

 invariably find it is an important item of bird food. If the validity 

 of depending upon the number of species as an index of frequency 

 be questioned, no matter. The tendency for feeding to be distributed 

 over the whole range of the available food organisms and in at least 

 rough proportion to the known abundance of the various groups, is 

 beyond dispute. 



This principle, predation in proportion to population, stands out 

 clearly in the tabulations of the animal food of nearctic birds here 

 presented and discussed. Compared to it the efifect of the so-called 

 protective adaptations on character of food is negligible. If these 

 adaptations controlled choice of bird food to a significant extent, 

 discrimination would everywhere be evident ; finding indiscriminancy, 

 on the contrary, we must conclude that the ruling criterion in choice 

 of food is availability. 



Indiscriminancy of Predators other than Birds 



Nearctic birds, as a group, are little influenced by the protective 

 adaptations of available prey. Let us see what can be said of other 

 classes of predators. 



Odonata. — In a general article on " Predacious Insects and their 

 Prey," Prof. E. B. Poulton says of a tabulation of dragonfly victims : 

 " Short as it is, the list is extremely interesting, and raises the expec- 

 tation that dragonflies will be found to prey rather largely upon 



* American instances are summarized in the following paper : McAtee, W. L., 

 The role of vertebrates in the control of insect pests, Smithsonian Rep. 1925, 

 PP- 415-437, 7 P's., 1926. 



