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NORTH AMERICAN FAUNA. 



Species. Visitant land birds, 26 species or subspecies. Resident water 

 fowl, 13 species. Visitant water fowl, 8 species. 



Of tbe 36 resident species or subspecies of land birds all but 5 were 

 observed by Colonel Grayson. These excei)tions are: Melopelia leucop- 

 tera, Tyr annus melanchoUciis couchi, OrnitJiion imherbe, Yireo flavoviridis 

 forreri^ and Thryothorus latvrencii magdalence. 



Twenty- four of the 36 resident land birds are specifically or subspe- 

 cifically distinct from their mainland representatives. Of this number 

 12 were described from Grayson's collections, 1 from Forrer's, and 11 

 from our own. A study of our collections from the islands, and near 

 San Bias on the mainland, brings out the interesting fact that several 

 species from the latter district show a decided approach to their island 

 representatives. This is very marked in Compsothlypis which is very 

 nearly the same at San Bias as on the islands. The Folyhorus and 

 Flatypsaris from that locality seem to be intermediate between the 

 island races and the birds of the mainland. Specimens of Thryothorus 

 felix from the same part of the coast are much nearer T. lawrencii than 

 they are to typical T. felix. 



Among the 24 species or subspecies of land birds peculiar to the 

 Islands 15 are larger than their relatives of the nearest mainland. 

 These are Columba f. 7nadrensis, Leptotila capitalis, Psittacula insularis, 

 Bryohates s, graysoni, JSyctidromus a, insularis, Amazilia graysoni, 

 Icterus graysoniy Cardinalis e. mariw, Firanga h. flammea, Yireo /. 

 forreri^ Yireo h, sordidus, Compsothlypis insularis, Granatellus francescce, 

 Thryothorus lawrencii and Merula graysoni. 



Six of the island birds average smaller than their mainland repre- 

 sentatives. These are Folyhorus c. pallidus, lache lawrencei. Flatyp- 

 saris a, insulariSj Myiopagis p. minimuSy Melanotis c. longirostris, and 

 Trogon a. goldmani. The two first named are generally smaller, but 

 Flatypsaris a, insular is has a longer tarsus, Myiopagis p. minimus a 

 longer bill and tarsus, Melanotis c. longirostris a longer bill, and Trogon 

 a, goldmani a longer bill and tarsus. 



Although Compsothlypis insularis also occurs in a limited area along 

 the coast, I have considered it as a typical island species. The 

 difference in size between island birds and their mainland repre- 

 sentatives varies greatly, being slight in some and very well marked 

 in others. Nyctidromus a. insularis is a larger bird than alMcollis 

 proper, but has a shorter bill and tarsus. Among the birds peculiar 

 to the islands Thryothorus lawrencii magdalence and Myadestes o. insu- 

 laris are almost the only ones which do not show more or less well- 

 defined differences in size from their nearest mainland relative; a series 

 of the first named, however, may show that it also differs. 



One of the most puzzling features of the fauna of these islands is 

 the absence of various land birds found on the adjacent mainland. 

 Although the physical conditions appear so much like those of the 

 mainland, yet some change must have occurred to upset nature's fine 

 balance and render these isolated areas unsuitable for many species. 



