I 20 Allen on Sexual Selection and the Nesting of Birds. [April 



species of birds of the groups here instanced — species too in which 

 the sexual difference of plumage is at a maximum — resort to 

 hollow trees for greater safety, as is the case with the Wood 

 and Mandarin Ducks (genus A/x),the Bufffe-heads (genus Clan- 

 gula), and the Sheldrakes' Merginae). In other cases, as in our 

 brilliantly colored Grosbeaks, where the female is dull-colored 

 as compared with the male, the male shares in the work of in- 

 cubation, and is even so indiscreet as to indulge in ecstatic out- 

 bursts of song while sitting on the eggs. 



Mr. Dixon's second group consists of "Birds in which the 

 plumage of both sexes is showy or brilliant in colour, and which 

 nidificate in open nests." "This group," Mr. Dixon says, "forms 

 one of those exceptions which, at first sight, appears seriously 

 to affect the reliability of the whole theory" ; but he believes "it 

 can be shown that the birds included in it may possibly secure 

 their safety in other ways." Unquestionably this is the case ; at 

 least they appear to get on quite as well as do the plain plumaged 

 open nest builders. It certainly is true that, as our author states, 

 many "brightly plumaged birds are safe enough in the locali- 

 ties where the}' build their nests." Mr. Dixon even suggests that 

 "Some gaily attired female birds may have no special enemies 

 against which to guard — their brilliant or showy dress is no dis- 

 advantage to them, as is the case with many conspicuous insects ; 

 and this fact may in itself explain why it is that the}' have 

 assumed such tints." He even supposes that as some brilliant 

 females may have become so through natural selection, the}' may 

 have altered the form of their nest from an open to a covered 

 structure; "and this would explain many of the apparent excep- 

 tions to the general rule that gaily dressed female birds sit in 

 covered nests." Unfortunately this is not susceptible of proof, 

 while the probabilities seem quite against the supposition. It 

 is true, as he adds, that we should '"also take into consider- 

 ation what colours are showy in certain haunts," — that while 

 they would be "very conspicuous in some places they may be 

 especially protective in others." 



The third and last group of open nest builders instanced con- 

 sists of those few species "in which the male is less brilliant 

 than the female," as the Phalaropes, Dotterel, Emu, etc. 



Passing to the second great division, 'in which the nests are 

 concealed,' the first group mentioned is composed of "Birds in 



