PARENTAL CARE AND NEST-MAKING 309 



gathering of her brood under her wings, for protection as 

 well as for warmth, is as eloquent as it is familiar. 



§ 6. The Case of the Cuckoo 



This seems a suitable place for a brief discussion of the 

 astonishing case of the Common Cuckoo, famous for its 

 evasion of parental responsibilities. The main facts are 

 these. The cuckoo is polyandrous, one female pairing with 

 several males. The eggs are laid at unusually long intervals ; 

 they are numerous and large for the size of the bird ; they 

 are very variable in colouring, but one female probably 

 produces only one type. With considerable stealth the 

 mother-cuckoo foists its egg into the nest of some other bird, 

 usually insectivorous, such as hedge-sparrow or meadow- 

 pipit, the number of different kinds of dupes being over a 

 hundred. If the nest be suitable she may lay her egg therein, 

 or she may lay her egg on the ground, lift it in her bill, 

 and place it quickly in the nest. With few exceptions 

 only one egg is placed in a nest. Of great interest are 

 the careful observations of Mr. Edgar Chance (1922), who 

 has proved that in some cases the cuckoo lays her egg in 

 the foster-parents' nest. But there are nests in which this 

 is impossible. 



In a small percentage of cases the coloration of the 

 cuckoo's egg closely resembles that of the foster-parents' 

 eggs, but this does not seem to be important. If it should 

 come to be of survival value that the cuckoo's egg should 

 have a particular coloration, there is an extraordinary wealth 

 of variations on which Natural Selection might operate. 



The egg of the cuckoo tends to develop more rapidly than 

 that of the foster-parents, and thus the nestling cuckoo is 

 able to oust the foster-parent's eggs or young ones. For 

 some eleven days after hatching it has a curious hollow on 

 its back which works well in the " dog-in-the-manger " 

 behaviour. Moreover, the young cuckoo is ultra-sensitive 

 to contact ; the touch of another young bird sends it into 

 almost epileptic convulsions, and it is very strong for its 



