54 . BIRDS' NESTS 



Possibly the Common Cuckoo {Cucidus canorus) has 

 the widest range of selection in this respect, a fact 

 which is confirmed by the exceptional amount of 

 variation presented by its eggs. Other species of 

 Cuckoos in the same genus ranging over a wide 

 expanse of country tenanted by vast numbers of 

 suitable foster parents may exhibit a similarly large 

 amount of variation in the coloration of their eggs, 

 but unfortunately our information is extremely 

 scanty. On the other hand such parasitic species 

 as the Great Spotted Cuckoo {Coccyzus glandarius), 

 which confines its unwelcome attentions practically 

 to birds of the Crow tribe dwelling in the localities it 

 frequents, lays eggs remarkably uniform in tint, and 

 somewhat resembling those of the Magpie. Outside the 

 Cuckoo family the only bird parasites at present known 

 to exist are certain species of American Icteridae, of 

 which the Cowbird {Molohrus pecoris) is by far the best 

 known {conf. p. 58). Whether the invading Cuckoo 

 breaks any or all of the eggs of the rightful owner of 

 the nest when paying her clandestine visits seems not 

 to be definitely known ; but with regard to the Cow- 

 bird and its allies Mr Hudson definitely states con- 

 cerning the South American species that both male 

 and female do actually destroy many of the eggs 

 of their dupes. Another very remarkable fact is that 

 one species of South American Cowbird (Molobrus 

 rufaxillaris) is actually parasitic upon another species 

 {M, badius), the latter making its own nest. 



