220 MR. C. F. M. SWYNNERTON ON THE 



captives^ preferences by wild individuals, albeit of other species, seems to me 

 to be of a particularly cogent nature. 



C. Methods of Experiment and Deduction. 



The plan on which I started (on Dec. 6th, 1908) was as follows : — 

 First to offer each of my captive animals as large a series as possible of 

 every available species of butterfly, and then, having thus ensured an adequate 

 knowledge of their butterflies by these animals, to carry out on each a series 

 of preference experiments by repeatedly placing together on the floor of the 

 cage a few freshly-killed butterflies of diiferent species and noting which 

 were chosen. 



For a time I was less successful than I had hoped, though, clinging nt first 

 to certain preconceived ideas and as yet knowing little of the factors that 

 should have been allowed for in shaping the experiments, I did not i-ealize 

 this then. I noiv find many of my earlier experiments very disappointing 

 reading indeed, and it is with a feeling of surprise at my own slowness and 

 ineptitude that I realize that I largely wasted five months (Dec. 6 to May 11), 

 534 experiments, and many thousands of butterflies in merely learning to 

 experiment. For it was apparently only towards the latter date that I was 

 commencing to realize at all sufficiently the vital necessity for keeping in 

 some sort of touch throughout an experiment with the state of the animaFs 

 appetite. It is also possible that the scale on which I attempted my series- 

 offering constituted rather a counsel of perfection : at all events, from one 

 cause or another, it was only in the case of a small proportion of my earlier 

 animals that lever arrived at the second or true preference-experiment stage. 

 Finally, the above-described method of preference experiment seemed when 

 I first tried it to lead to results as difficult of interpretation as those that 

 Colonel Manders (Proc. Zool. Soc. London, Sept. 1911, pp. 696-749) obtained 

 by the same method in Ceylon. I have since (by repeated observation on 

 several species of birds, wild and tame, and one mammal — Petrodromiis tetra- 

 dactylus) found the explanation to be that an insectivorous animal, given a 

 choice, either fails to exercise it, as between the things he is hungry enough 

 for and merely picks up each as it comes, or, when he does exercise it, tends 

 to select the largest object that he is at the moment hungry enough to eat : 

 were he hungry enough for Amauris domimcanus he would probably take it 

 in preference to Precis cehrene. When this is realized and allowed for, this 

 method, first suggested to me by Mr. Marshall, is not only exceedingly useful 

 but probably the only one that can in most cases be satisfactorily employed in 

 dealing with wild birds. I had, however, in any case attempted very little 

 in the way of preference experiments at all before May 12th, 1909, when 

 I commenced a short series of experiments on one of my buzzard-eagles 

 {Asturinula monogrammica), in the course of which I evolved what is now 

 my more usual method of eliciting preferences. 



