124 NATURE SKETCHES IN TEMPERA'TE AMERICA 



these assemblages, often numbering several hundreds, were 

 fresh and bright appearing and without blemish. 



I do not recall in Herrick's work on the "Home Life of Wild 

 Birds" a single instance of a butterfly being taken to the 

 nests of young birds during the feeding process, yet he notes 

 carefully many other insects fed by parent birds to their young. 



Herrick, in describing the action of nestling cedar birds, 

 says: "They snapped at every ant and flying insect which came 

 within their reach, but I never saw a ^single capture. The 

 preying instinct is undoubtedly one of the most ancient among 

 animals, and young birds peck instinctively at all kinds of 

 small objects, but precision of aim which leads to success in 

 capturing their prey must be acquired by practice." 



The difficulty experienced by adult birds in catching butter- 

 flies while flying must be very great, and young birds would 

 find the task of catching them still much greater. Then, 

 after pursuit of butterflies, if the birds finally caught one of 

 these insects, and found it distasteful, what a disgust would 

 be formed for them. In such an event the species of butterfly 

 in question would after a time enjoy immunity from further 

 attacks. All evidence considered, our higher birds have 

 acquired a dislike for many butterflies, and they form but a 

 minimum portion of their diet. This cannot be said of many 

 insect larvae, flies, beetles, locusts, grasshoppers, katydids, 

 dragon-flies, and so forth, all of which are preyed upon freely 

 by birds. Young birds are taught to some extent by the parents 

 what to eat, and as a result there has arisen a kind of special 

 diet for each species of birds. 



From this line of reasoning it follows that a former promiscu- 

 ous diet among birds might become restricted, and this means 

 the exclusion of some distasteful butterflies. The latter may 

 have been eaten in generations past, but are now immune. 

 If birds were the selective factor in perfecting the supposed 

 mimicry or resemblance of the Viceroy butterfly to the Monarch, 

 the bird-eating factor must have exercised the selective influence 

 in time past, more than at present. At least it is so deduced 

 from observations. While the adult butterfly enjoys a large 

 share of immunity from birds, I am not in possession of facts 

 as to how much destruction is caused the larvae and pupae by 



