284 Mr. J. L. Bonhote on Birds 



All these specimens come from New Providence, the two 

 extremes being taken in the spring of the year and the 

 intermediate form in the autumn. 



To my mind, the best explanation is that G. rostrata is the 

 bird in its first year (i. e. from its 1st to its 2nd autumn), 

 and G. maynardi the fully adult bird ; and this conclusion is 

 borne out by my intermediate specimen being an autumn 

 bird in the moult. 



Mr. Bangs, however, states that there is a difference in 

 size between the two species, and since, as a rule, birds reach 

 their full growth in their first year, the size of G. ros- 

 trata and G. maynardi, if my solution be the correct one, 

 ought to be the same. On looking through Mr. Bangs's 

 measurements in the paper quoted above we find no definite 

 break between the two species, the one running right into the 

 other. Still, supposing that the two sets are marked by a 

 division, on looking more closely at those measurements we 

 find that the difference lies only in the wing and tail. Those 

 relating to the tarsus and culmen, the only skeletal measures 

 given, are precisely the same in both series, so that struc- 

 turally the two so-called species are identical so far as size 

 is concerned, and the apparent difference is due to the length 

 of feathers, which are moulted at a time when I suggest that 

 the transition takes place. 



The only evidence which I have to leave untouched is the 

 question of the song, which is said by Maynard to be 

 different ; but might not age affect this also ? 



Apart from these arguments, surely to those who believe 

 in the principles of evolution, as all systematists of the 

 present day are bound to do, it is practically an impossible 

 matter that two such nearly allied resident species, having 

 the same habits, should exist on an island of some 80 square 

 miles in extent. Supposing that they reached the island as 

 two separate forms, they would be bound to approximate and 

 merge together; or supposing, which is almost certainly the 

 case, that they arrived on the island as one species, in what 

 manner could natural selection so act as to produce two 

 distinct species on one small rocky island, without hills, 

 rivers, or any pronounced geographical features ? 



