i64 BIRD BEHAVIOUR 



progenitively inclined, the rearing of one brood 

 satisfying as a rule both wild and domestic species 

 of this character for the year, even the pampered 

 park Mallard not breeding in autumn, though they 

 pair • and among the birds which have helpless 

 young, or at any rate young which have to be fed, 

 the least fertile, i.e. those which lay but one egg 

 at a time, are also the least apt to want to repeat 

 the process. The diving rock-birds which throng 

 our cliffs, for instance, depart to sea quite content 

 with their single chick. 



Pigeons, however, are quite willing and anxious 

 to repeat their task of rearing twins as often as 

 occasion allows, that is to say, as long as they can 

 get plenty of food. I have seen Wood-Pigeons in 

 Regent's Park, where conditio are exceptionally 

 favourable, pairing at Christmas in very cold 

 weather, and in India nests of the commonest 

 species of Turtle-Doves are to be found practically 

 all the year round, so that these birds apparently 

 are always ready to breed, except, no doubt, when 

 moulting, at which time the most enthusiastic 

 nesters have perforce to postpone operations. 



Ordinary passerine birds, also, frequently rear 

 two or even more broods in a season, so that even 

 when their sittings are individually less in number 

 than those of birds with active chicksj their total 

 output for the year is larger. There are also certain 

 individual species which have ' a special bent for 

 procreation, and will commence nesting on less 

 provocation, if I may so express it, than any others ; 



