5 8 Barrett. Parasitical Habits in the Cuculidcc. [ ^^^ 



Emu 

 Oct. 



Thrushes. In the Great Spotted Cuckoo {Coccystis glandarms), 

 ranging through south-western Europe, Asia Minor, and Africa, 

 we can see the instinct to shirk parental cares yet more highly 

 developed. These birds are truly parasitical, inasmuch as they 

 foist their eggs on certain species of Crows and Magpies whose 

 eggs bear a marked resemblance in colour to their own. In 

 this case, however, several Cuckoos' eggs are found in the same 

 nest, and when these are hatched out it is stated that the intruders 

 live in perfect harmony with such of their foster- brethren as 

 have survived, and make no attempt to eject them. Occasion- 

 ally the female Spotted Cuckoo, before laying in the chosen 

 nest, breaks the eggs of the rightful owner, in order to make 

 more room for her own. Thus we find the parasitical habit and 

 instinct to eject fellow-nestlings being manifested in various 

 stages of development by certain existing representatives of 

 the CuculidiC. 



Concerning the origin of these instincts or habits, the theory 

 that natural selection, acting during a long period of time upon 

 a chance beneficial variation in habits displayed by an early 

 progenitor of the race, is responsible for the habit, receives much 

 support from a further fact. Certain birds have been known to 

 lay eggs in the nests of others belonging to widely different 

 genera. Moor-Hens' eggs have been found in a Coot's nest, and 

 an egg of the former species was taken in the half-finished home 

 of a Blackbird. Starlings eject Woodpeckers from their nesting- 

 holes in trees and the eggs of Gulls and Eider Ducks have been 

 noticed in each other's nests. Romanes, in his "Animal Intelli- 

 gence," says that we are justified in setting down the Cuckoo 

 instinct to the creating influence of natural selection, and a con- 

 sideration of the facts just mentioned will show how easily the 

 parasitic instinct may have originated. The practice is by no 

 means confined to birds, and an interesting comparison may be 

 made between birds and insects by referring to the habits of a 

 certain kind of bee, which always consigns its eggs to the care 

 of another species. These parasitical insects are structurally 

 modified in obedience to the law of co-ordination of structure 

 with function and habit, for they are devoid of the pollen-gather- 

 ing apparatus, which would have been absolutely essential had 

 they been obliged to rear their own offspring. 



There are two other phases of the Cuckoo problem that I 

 should like to touch upon briefly, viz. : — 



(i.) The resemblance that certain Cuckoos' eggs bear to those 

 of the chosen foster-parent. 



(2.) The nature of the impulse acting on a newly-born Cuckoo 

 and causing it to eject its fellow-nestlings from their home. 



As regards the first much-debated point, it is interesting to note 

 that the Great Spotted Cuckoo {C. g/andarms) of South Africa 

 lays eggs closely resembling those of certain Crows and Magpies 



