Birds in Belat'wn to their Prey. 101 



insects, occur as between any two species of birds, and, for 

 that matter, any two individuals of the snme species. 



It is interesting to note how the experiments described in 

 this paper bear on the above. Nauseation of Ii'risor by 

 J)anaina3 and Acrreinre eaten beyond their respective safety- 

 limits has already been I'eferred to. The quaint shaking up 

 again of a swallowed Alijlothris in experiment 540 by Loplio- 

 ceros melanoleiicKs, and the same bird^s attempted shaking 

 up again of the yet higher-grade butterfly, Neplis^ on another 

 occasion, are probably to be explained on the same lines : 

 each had been rashly eaten after its normal refusal-point had 

 been passed. I have had numerous other instances of insects 

 swallowed and brought up again at once, and it seems to me 

 that many liirds, at any rate, are often able to gauge an insect's 

 effect directly it approaches the glandular stomach, perhaps 

 through sensations arising from the stimulation and in- 

 hibition, respectively, of the digestive secretions *. In tliis 

 last point we have, I believe, the whole explanation of the 

 phenomena we have been considering. In my later and 

 more knowledgeable experiments I found myself able to 

 restore my animals' fading appetites, and to enable them to 

 eat with impunity prey that they were already refusing, by 

 giving them special dainties, and (in carnivorous animals) to 

 spoil their appetites and make them refuse what they would 

 otherwise have readily eaten by letting them see, smell, or 

 taste the equivalents of AcrcBa and Danaida when they were 

 by no means ravenous enough for them. It is probable, in 

 other words, that certain insects, eaten eagerly to repletion- 

 point, have the stimulative effect on a bird's digestive secre- 

 tions that roast beef and certain soups have on our own, 

 while others, such as the Danaina>, tend definitely to inhibit 

 the secretions, and can only be digested, or even retained, 



* Applied to frugivorou3 birds, this, witli parental guidance, might 

 explain sufficiently their learning to avoid poisonous fruits without 

 being killed in the process. It is also no doubt perfectly true that 

 fewer fruits are highly poisonous to birds than to us. The fact 

 that birds are readily destroyed by powerful poisons concealed in foods 

 in which they have learned to place perfect conlidouce is no objection. 



