88 THE ASIATIC FUR-SEAL ISLANDS. 



PROPORTIONATE NUMBER OF SEXES AND AGES ON ROOKERIES. 



A question whicli of late has been given considerable prominence is that of the 

 relative number of breeding females and old bulls on the rookeries. Upon this, and 

 upon the closely connected one as to the number of females a bull is able to serve, 

 there has been a great diversity of opinion.^ My experience this summer leads me to 

 the belief that, on the wJiole, a bnll is able to take care of as many females as he can 

 keep around him. There is undoubtedly great individual differences in this respect, 

 some bulls being stronger than others, but I think it can be safely asserted, as a rule, 

 that the procreative power of the bull is in direct proportion to his general physical 

 strength. I think it also sound to assume that, as a rule, a bull physically strong 

 enough to live through the winter gales and the vicissitudes of his winter wanderings 

 and to return to his place on the rookery is also strong enough to fulfill his duty there. 

 I have purposely emphasized "on the whole" and "as a rule," because I can easily 

 imagine individual cases of, for instance, accidentally castrated bulls, or old feeble ones 

 who might have the good fortune to meet with unusually favorable conditions during 

 their winter migrations, etc., and because I am quite willing to admit that a number of 

 such bulls may be found on each rookery. These exceptions, however, do not materially 

 alter the above propositions as relating to the whole population of the rookery. 



The train of reasoning which led me to the above conclusions is as follows: Some 

 of the most noteworthy of my observations this summer on the Commander Islands 

 establish the facts (1) that the decrease in the killable seals was most marked on Cop 

 per Island; (2) that there was a full complement of pups as compared with breeding 

 females on both islands; (3) that there was an ample supply of bulls, old and young, on 

 Copper Island, while on Bering Island they were much less numerous as compared with 

 the number of females. I was informed that the latter condition was not peculiar to 

 the present year (1895) alone, and it is also particularly mentioned in Mr. Grebnitski's 

 report for 1893. It would therefore seem as if the different proportions between the 

 sexes on the two islands have had no visible influence upon the number of pups born. 



The soundness of the above deductions may receive corroboration, or the reverse, 

 by observations on the south rookery on Bering Island in 1896. On that rookery 

 the disproportion between the two sexes was excessive in 1895. According to reliable 

 information the number of bulls on the whole rookery did not exceed flve.^ Judging 

 from what I saw of this rookery during two visits, I should place the number of 

 breeding females at about 600, possibly only 600. It would be a comparatively easy 

 matter to observe this year whether the number of pups born be very markedly small 

 in proportion to the number of females hauling out. 



On the large rookeries it is difBcult, if not impossible, for various reasons, to 

 correctly estimate the average proportion between the bulls and the females, and 

 particularly so on Bering Island, because the bachelors to so great an extent haul up 



1 While maintaining that the value of the guesses as to the number of females a bnll is able to 

 serve is of necessity very dubions, I may mention that Mr. Kluge, who for eight years spent the summer 

 upon Tiuleni Island with the seals practically under his very eyes the whole season, informed me this 

 summer that "he does not for a moment believe that twenty-five females to a bull are in the least too 

 many," though he did not venture to guess at the maximnm. 



^When I visited the rookery on August 17 the bu]ls had already left. It was rumored in the 

 village that there had only been one bull, but Nikanor Grigorief, the native in charge of the killing 

 there, informed me that the actual number was five. 



