52 BIRDS' NESTS 



in which certain individuals of a species will return 

 each season, not only to the same locality, but in 

 many cases to the same precise spot for nesting 

 duties. Birds that pair for life appear to have this 

 nostalgic impulse very highly developed, and this 

 applies not only to sedentary species but to migra- 

 tory ones as well. The Magpie, for instance, is no 

 more deeply attached to its old nest, that it visits 

 from time to time all the year round, than is the 

 House Martin to its mud-built cradle beneath the 

 eaves, to which it unerringly returns after a journey 

 of many thousands of miles and a continuous absence 

 of seven months. Both these species pair for life, 

 and the nest seems to be a home centre, a trysting 

 place of an irresistibly attractive kind. 



We now pass to the consideration of another class 

 of non-nest-building birds, what we have ventured to 

 call " parasites." These we can scarcely describe as 

 nestless birds, for their young are hatched and reared 

 in nests — not the discarded homes of other species — 

 the eggs being surreptitiously inserted during the 

 absence of the rightful owners, the latter incubating 

 them and rearing the chicks with every care. The 

 Cuckoo, of course, is the most familiar instance to 

 British naturalists of these bird parasites, but the 

 curious habit is by no means confined to that species, 

 not only prevailing widely in the family to which "the 

 Messenger of spring " belongs, but in another group 

 as well. There can be little doubt that the parasitic 



