THE ENVIRONMENT AND REPRODUCTION 37 



and other instances have been discussed by Fox^^ and 

 Baker.io Regarding vertebrates there is still not a great 

 deal of information. However, it is probable that both 

 the Californian smelt, and the New Zealand whitebait 

 spawn only at particular phases of the moon, the process 

 being repeated during two or three successive months, 

 although of course such action by a marine species may 

 be related more to the state of the tide than to the light 

 of the moon. 



Regarding the amphibians, reptiles and mammals, 

 nothing appears to be known, although the possibility 

 of an effect cannot be discounted. The breeding of bats 

 may be remembered in this connexion, and it is not 

 impossible that the precise nature of the breeding season 

 of Miniopterus in the New Hebrides may be ensured in 

 this way, the effect of the moon being to impart great 

 accuracy to the timing of an internal rhythm with 

 approximately a yearly periodicity. 



Among birds there are indications that ovulation in 

 the nightjar, a crepuscular species, is controlled by the 

 moon. Wynne-Edwards has described how the twa eggs 

 are laid during the last quarter of the lunar cycle so that 

 the chicks are reared during the next full moon when 

 hunting can continue all night. ^^'^ Similarly, it has been 

 showni32 that when the eggs of a nightjar are taken a 

 period of three weeks must pass before the bird can lay 

 again. This is unlike the other species which have been 

 studied, and the contrasting case of the flicker has been 

 mentioned in which the steady removal of eggs has 

 resulted in the production of 73 eggs in 93 days. 



Another environmental variant which is particularly 

 important in the tropics is rain. In these regions the 

 alternation of dry and rainy seasons is normal, and there 

 is a great deal of evidence that this change in some way 

 controls the breeding habits of many tropical species. 

 Frequently birds breed when the rains begin. An 

 Australian cockatoo, Kakatoe roseicapillay does this, and 

 it may miss a season altogether if the rains fail.i^s 



