1917-] Breediny-habits of the Cuckoo. 203» 



(/) Generally speaking, by far tlie most complete resem- 

 l)laiice ill colour to the eggs of the foster-parent occurs in 

 the case of foreign species of Cuckoos, which deposit tlieir 

 eggs in the open nests of species nearly related to each 

 other, 



(//) In Germany, however, the most complete similarity 

 in the eggs of C. caaorus most often occurs when the eggs 

 are placed in the nest of the Common Redstart, a species 

 which breeds in holes. 



Such curiously contradictory facts have, needless to say, 

 produced very varying tlieories. 



The general consensus of opinion, including such autho- 

 rities as J3aldamns^ Rey, Professor Newton, and others, 

 favours the theoiy that the Cuckoo, whenever possible, 

 deposits her eggs in the nest of that species by which she 

 herself ivas reared., and that, provided sufficient nests of such 

 species are available, this habit is transmitted to her pos- 

 terity and we have what are termed " Hedge-Sparrow 

 Cuckoos," " Meadow-Pipit Cuckoos,'^ etc. 



It is also a generally accepted fact that each female 

 Cuckoo lays eggs of approximately the same type all 

 her life. 



After this, however, the theories diverge rather widely. 

 Baldamus, in 1853 and 1854, explained the resemblance 

 of the eggs of the Cuckoo to those of the foster-parents by 

 concluding that the Cuckoo, whenever possible, deposits her 

 eggs in the nests of those species ivhuse eggs most resemble 

 her own, and only selects others when it is not possible to 

 find such nests. 



This was opposed " in tolo " by Adolph Miiller, who con- 

 sidered it the exception for any resemblance to occur, but 

 liis facts and arguments are neither numerous nor convincing. 

 He states that the species selected as foster-parents will not 

 only incubate eggs of a totally different colour to their own, 

 but even bits of lime. Yet, later on, he quotes the cases 

 of a Yellow-Haramer and Whitethroat who ejected the 

 Cuckoo's egg, presumably, he says, because they detected 



