1903 Moffat. — The Spri?ig Rivalry of Birds. 159 



that gentleman '' used during several years to shoot one of a 

 pair of Starlings which built in a hole in a house at Black- 

 heath, but found that the loss was always immediately re- 

 paired. During one 3^ear Mr. Engleheart kept an account, 

 and found that he had shot thirty-five birds from the same 

 nest ; these consisted of both males and females, but in what 

 proportion he could not say. Nevertheless, after all this 

 destruction a brood was reared." 



I think it appears to be established by such records as these 

 that there is a reserve of non-breeding birds, and, moreover, 

 of birds perfectly willing to breed — and that they are of both 

 sexes. The puzzling question is, why don't they breed until 

 vacancies occur in the partnerships already existing ? 



This question occurred to Darwin when he was working at 

 the subject of *' Sexual Selection." - *' How is it that there are 

 birds enough ready," he asks, " to replace immediately a lost 

 mate of either sex ? " He considers several possible reasons, 

 such as that some birds are mateless through having had 

 their nests destroj^ed, or their partners killed ; and that some 

 have mates for whom they do not particularly care. But 

 these explanations, as Darwin at once saw, were of little 

 value ; for if, as he goes on to express it, " so many males and 

 females " are ** always ready to repair the loss of a mated 

 bird," it is impossible to refrain from asking, "Why do not 

 such spare birds immediately pair together ? " And to this 

 question Darwin suggests the answer, which he gives as his 

 final clue to the difficulty, that these unmated birds — though 

 all of them willing for matrimony in the abstract — sre not in- 

 dividually pleasing to one another, and, therefore, will not 

 have one another for husband or wife. 



Now this is a rather romantic explanation, which, I fear, 

 will not stand the cold light of arithmetic ; because it is 

 as certain as any arithmetical fact can be, that if you shoot 

 07ie of a pair of nesting birds thirty-five times, or even half-a- 

 dozen times, during the season, and kill birds of both sexes, 

 you will have killed both the original members of the pair, 

 and therefore the two who are living together, a happy 

 husband and wife, at the close of the season, must be two of 

 the very lot who " ex hypothesi'' (as the Mathematicians say) 

 were "not pleasing to one another." So the romance of the 

 situation seems to vanish. Not only, we find, are these non- 



