150 BIRD BEHAVIOUR 



mous masses in the South Pacific, quite equalling 

 the old-time flocks of Passenger Pigeons. 



At any rate, such facts as these look as if one- 

 egg-laying were a good habit for survival ; but at 

 the same time we must remember that the birds 

 above quoted are conspicuous for living or at any 

 rate breeding, in masses, thus giving a false impres- 

 sion of their numbers as compared to more scattered 

 species ; that most of them draw their living from 

 the hospitable storehouse of the sea, and that two 

 of them did not stand long against human destruc- 

 tiveness at any rate, and might not have withstood 

 the invasion of any other carnivore. 



Moreover, some of the single-egg-layers are 

 scarce birds ; the Condor and Lammergeier are 

 not nearly so common as the smaller Vultures — I 

 only saw two of the latter during all my residence 

 in India ; and the large Hornbills, which lay only 

 one egg, are always rare where the smaller and more 

 prolific kinds are common. There may be in some 

 cases good reason why only one egg should be laid, 

 as wiU appear in the consideration of some curious 

 incubation and nursing habits, but it is a quite 

 possible consideration that birds which lay only one 

 egg are on the decline as species through infertility, 

 since one egg a year — and sometimes even one in 

 two years, as is said to be the case with some of the 

 great Vultures — 'is a perilously low output, and the 

 sea-birds are liable to numerous accidents. 



And as to actual numbers, it is highly probable 

 that such birds as the Quail and Skylark, which are 



