Nest-building, Incubation, and Migration. 239 



nests of its own species, and not the equally good, or per- 

 haps, better nests of an allied species. The subject is full of 

 difficulties whichever way it be regarded. And if we ask 

 by what steps the Baltimore oriole has come to build 

 his hanging nest in just that particular fashion, we can 

 only reply, evasively, that with all our advances in biologi- 

 cal knowledge a child can still ask questions which its 

 elders find it hard to answer. 



The laying of eggs in the nest when it is built is un- 

 doubtedly a habit of congenital origin ; and problems of 

 interest and some difficulty arise out of a study of the 

 colour and markings of these eggs. These problems are 

 not directly connected with habit and instinct, and they do 

 not therefore call for consideration here. But the strange 

 and abnormal habits of the cuckoo demand some notice. 



The cuckoo (Cuculus canorus) is in several respects an 

 anomalous bird. " He is a ' vagrom man/ as Dogberry 

 would say : a vulgarian, a disreputable parasite. Yet he 

 is in some ways an interesting creature, and the world 

 has," Mr. Cornish,* reminds us, " always a fondness 

 for interesting scamps." In the matter of food, he 

 will eat hairy caterpillars which are rejected by most 

 birds. There appears to be a great preponderance of 

 males, the proportion being variously estimated at from 

 twenty, to five to one. Mating is indiscriminate ; and 

 polyandry prevails. The hen bird lays a largish number 

 of eggs, some say at relatively long intervals of several 

 days. According to the careful observations of Dr. Eey, 

 however, the hen cuckoo lays an egg every other day, from 

 the middle of May till the middle of July, and, at times, 

 lays one every day for short periods. They are remarkably 

 small for the size of the bird, and are somewhat variable 

 both in this respect and in that of coloration. They are 



* "Wild England of To-day," p. 108. 



