VIU INTRODUCTION. 



of a bird as a subspecies) how island forms can be reduced to this 

 rank. If there be no possible intergradation, the birds must, 

 according to ornithologists holding this yievr, be specifically- distinct. 

 I am, of course, of opinion that where a species intergrades into an 

 allied form, the latter is a subspecies ; but I do not consider that 

 without proof of distinct intergradation a bird must necessarily 

 merit specific rank and fail to be regarded as subspecificallj' distinct 

 only. Some island forms, although they may certainly differ 

 slightly from typical birds, have differences so suggestive of cli- 

 matic variation only and not of specific value, that I take them upon 

 their own merits and assign them a position accordingly. 



The most serious difficulty, however, presents itself in treating of 

 the CoJaptes of North America, C. auratus and C. mexicanus, and 

 the intermediate form termed C. ayersi. Whether we accept the 

 strong evidence of the late Professor Spencer Baird and regard the 

 varied race as the result of hybridization, or whether we adopt the 

 views of Mr. J. A. Allen, who is not in favour of such a theory, and 

 seems rather to consider the variation as the result of climatic 

 influence and of a change in the conditions of environment, or 

 whether we follow Dr. Elliott Coues, who suggests that it may be a 

 transitional form, it is evident that a difi[iculty must arise in 

 endeavouring to ascertain whether the intermediate birds which 

 are found at a great distance from the point of junction of C. auratus 

 and C. mexicanus are really beyond the radius to which a change 

 would extend, or whether beyond that to which some of the inter- 

 mediate birds might wander, or whether such change in individual 

 examples be a sign of a reversion to a remote ancestral plumage. 

 I am certainly in favour of the theory of interbreeding, and I see 

 no insurmountable difiiculty, by adopting such a view, in accounting 

 for certain characters, suggestive of hybridization, appearing in a 

 remote region where no interbreeding of C. auratus and C. mexi- 

 canus could possibly exist. It may be that the ancestors of the 

 Colaples had the red malar stripe in the male, and the black stripe 

 in the female, and a red nuchal band may have existed in either 

 one or both sexes, and the differentiation in succeeding forms would 

 not preclude reversion to the original one, — in fact, it is what might 

 he looked for. 



