60 



NORTH AMERICAN FAUNA. 



Although Myadestcts obscuriis insularis is very closely related to occi- 

 dentalis, yet it may be distinguished by several slight but constant 

 characters, such as the greater extension and paler shade of ashy from 

 the neck over the forward part of the back. The lower parts also are 

 paler, especially on the throat and abdomen. The white tips to the tail 

 feathers, mentioned by Dr. Stejneger as characteristic of this form, are 

 equally common on specimens of occidentalis. 



The following measurements show the relative size of the two forms: 



Measurements of Myadestes obscurns insularis and Myadestes o. occidental}*. 



Hylocichla ustulata (Nuttall). Russet-backed Thrush. 



A typical sp ecirnen of this species, taken on the islands by Colonel 

 Grayson in the winter of 1865, is in the National Museum. In his 

 notes Colonel Grayson says: "I found this little thrush in the mouth 

 of January quite abundant in the thickest of the woods of the Tres 

 Marias. It is very timid and shy, more so than any bird I saw upon 

 the islands; it frequently uttered a low, plaintive whistle, and seemed 

 solitary in its habits." We saw none of them on the islands in May, 

 and it is safe to class them as winter visitants. 



Hylocichla ustulata swainsonii (Cabanis). Olive-backed Thrush. 

 Hylocichla ustulata almce Oberholser, Auk, XV, p. 304, October, 1898. 



Two specimens of this thrush were taken on Marie Madre, one on 

 May 5, the other on May 19. They were found in the heavy forest back 

 from the coast, and evidently occur only as stray migrants. 



Mr. Oberholser mentions these specimens as typical examples of his 

 subspecies, which is considered a synonym of Hylocichla u. moaimonii 

 by the American Ornithologists' Union. 



Merula graysoni Ridgway. Tres Marias Robin. 



Turdus flavirostris Grayson, Proc. Boston Soc. Nat. Hist., XIV, p. 27fi, 1871 (part) ; 



Lawr., Mem. Boston Soc. Nat. Hist., II. p. 26G, 1874 (par; j. 

 Merula flarirostris graysoril Ridgway, Proc. U. S. Nat. Mus., V, p. 12, 1882. 



Gray son's robin is one of the most abundant and widely spread resi- 

 dents and takes the place of M. flavirostris of the mainland, which it 

 closely resembles in habits and general appearance. Although a char- 

 acteristic bird of the islands, yet occasional stragglers reach the main- 



