Vol. XXXVI II n „, OAO 



1920 Correspondence. oQo 



ous birds have more or less regular beats which they cover approximately 

 on schedule. This means they do repeatedly go over the same trees; 

 but in their territory they undoubtedly make excursions, for when we 

 test them by exposing food supplies they quickly find them. Their sys- 

 tem of food-finding, like that of various other animals (as ants and mice), 

 is, I am convinced, to look everywhere in their domain. They have all 

 their time for the work, and searching all day every day, in the compara- 

 tively restricted area, to which most birds at any given time, appear to 

 confine themselves, it is inevitable that the same spots will be inspected 

 again and again. 



The appeal to theory when observed facts really have nothing particu- 

 larly mysterious about them, seems to be due to taking too seriously the 

 so-called "struggle for existence." Except at the breeding season, an 

 individual bird has practically nothing to do but to search for food. Under 

 anything like normal conditions there must be no great difficulty in secur- 

 ing the required amount. In fact in the case of Audubon's Warbler and 

 numerous other birds of mixed feeding habits there is always available 

 a reserve food supply, in the form of overwintering fruits, upon which 

 the birds can draw at will. Such birds, therefore, distinctly are not under 

 constant pressure of necessity of food-finding. They at least have leisure, 

 though their actions may belie it. In the writer's opinion, all birds, 

 normally, are not in dire straits for food. Of the smaller species, at least, 

 I would say, they make countless unnecessary excursions, they peck a 

 hundred times for each morsel of food secured, they are, they must, they 

 will be busy. This ceaseless unproductive activity in itself is sufficient 

 evidence that the struggle for existence is not the gripping, controlling 

 thing some would believe. 



In conclusion I would mention briefly certain other points in the two 

 papers reviewed that seem rather too highly tinged by theory. The sense 

 of direction, admittedly marvellously developed in certain birds, is not 

 entirely occult to man. Australian natives and other savages have been 

 recorded as having it in marked degree and civilized man certainly does 

 not entirely lack it. The wonderful cases of male insects finding females 

 immediately after issuance from their pupal cases certainly are more 

 satisfactorily explicable on the basis of a finely developed tropic sensitivity 

 than on an occult mate-finding sense. Results of experiments certainly 

 support this view, since female moths emerging in indoor cages, as in 

 greenhouses, have attracted numerous males, though the circumstances 

 could not agree in the province of any mate-finding sense that would have 

 developed under natural conditions. In other words, since greenhouses 

 have never been part of the normal environment, an "occult" mate- 

 finding sense developed by natural selection would not take male moths 

 into such a structure. However, a very sensitive tropic reaction would 

 take them there or to any other accessible place where the excitatory 

 object, the female, happened to be. 



