BIRDS OF THE TRES MARIAS ISLANDS. 



49 



forest within a mile or two of the seashore and kept among the branches 

 of trees and bushes within 10 or 15 feet of the ground. Its habits 

 were the same as on the mainland. 



A careful comparison of series from the islands and the mainland 

 shows but little difference. The island birds are slightly grayer on the 

 back, the bills average a little longer and wider, and the tarsus is longer, 

 but these differences are too slight to warrant subspecific recognition. 

 Unfortunately the type of this subspecies is based on a winter specimen 

 from Santa Eugenia, Oaxaca, near the border of Chiapas. This leaves 

 the summer range of typical birds in doubt. 



Below are averages of specimens from the islands and the mainland: 



Measurements of Myiarchus lawrencei olirascens. 



Contopus richardsonii (Swains). Western Wood Pewee. 



During the first ten days of May these birds were not uncommon in 

 some of the denser growths of small trees along the lower slopes of Maria 

 Madre. None were seen on the other islands and they all disappeared 

 a little later, showing that they were merely stray migrants. The 

 single specimen taken is identical with others from the western United 

 States. 



Empidonax difficilis Baird. Western Flycatcher. 



These birds were very sparingly distributed on the Tres Marias. 

 They were seen on Maria Madre soon after our arrival, and on May 27 

 one was taken on Maria Magdaleua. They were usually found in dense 

 thickets and along shady canyons. Colonel Graysou records them 

 as common, but they undoubtedly occur only as winter visitants and 

 migrants. 

 Ornithion imberbe (Sclater). Beardless Flycatcher. 



Two specimens were taken and a few others seen early in May on 

 Maria Madre; none were seen later, and they probably occur merely as 

 stragglers during migration. They move about like small vireos in the 

 tops of low trees and in large bushes, searching the outer twigs for 

 insects and flying out every now and then to capture one on the wing. 



A series of specimens from various localities on both coasts and the 

 interior of Mexico, the Tres Marias Islands, and southern Arizona fails 

 to show any tangible characters to distinguish 0. imberbe ridyicayi 

 from typical 0. imberbe. 

 13950 No. 14 i 



