BIRDS OF THE TRES MARIAS ISLANDS. 55 



ous ainoug tbe trees ami tall bushes about the few springs and little 

 streams near the summit. A few were also seen in similar places on 

 Maria Magdalena. Vireo f. forreri occupies the lower slopes, while 

 sordidus occurs mainly higher up, the ranges of the two birds being 

 complementary. The Tres Marias vireo is usually found at a medium 

 height among the foliage of thick-topped trees, rarely ascending to tlie 

 extreme top. It was also often seen in the dense, tall undergrowth 

 near water. 



Compsothlypis insularis (L.awr.). Tres Marias Pariila. 



Panda iiisitlarin Lawr., Anu. Lye. Nat. Hist., N. Y., X, p. 4, 1871; Grayson, Proc. 

 Boston Soc. Nat. Hist., XIV, pp. 278, 300, 1871; Lawr., Mem. Boston Soc. Nat. 

 Hist.,n, p.2fi9, 1874. 



These pretty little warblers were the most abundant of the land birds 

 on the Tres Marias. A few of them were also founc on Isabel Island, 

 and the only Compsothlypis taken on the mainland at San Bias belongs 

 to this species. They frequent the thin forest of the lower slopes ou 

 the Tres Marias, and dozens of them were seen during every visit to tlie 

 woods, and they were seen in smaller numbers ou the higher slopes. 

 Many also came familiarly into the small trees and shrubbery about the 

 houses at the settlement. They were always l)usily at work in pursuit 

 of insects among the branches, and searched the bark of small shrubs 

 near the ground as well as the branches at the tops of large trees. 

 They were rather common in the scrubby growtli of stunted trees ou 

 Isabel, and were very abundant in the tree tops of the heavy forest on 

 the maiidand between San Bias and Santiago. Their song is weak and 

 lisping and not at all musical. 



There is little doubt that a good series of specimens will demonstrate 

 thut Gn7npso1hlypis pitiayumi o( northern South America is represented 

 in Central America and Mexico by a number of geographical races 

 rather than by the closely related species now recognized — G. inoriiata, 

 C. puJchra, C nif/rilora, and G. insularis. Even the imperfect series at 

 hand shows signs of iatergradation, but treating G. insularis as a 

 species for the present, its differences from its nearest relative, G. 

 pulelint^ are set forth in the following notes. G. pitlchra. was the only 

 form found on the mainland back of the low coast plain, on the tropical 

 or subtropical slopes of the mountains. This species was described 

 Irom Cldliufthua, and api)ears to bf a resident of the lower slopes of 

 the Sierra Madre, ranging from tJhihuahua to Te[)ic, while ('. insularis 

 is characteristic of the hot lowlands on tlie coast near San Bias and the 

 outlying islands. 



G. insul((ris is larger than G. ptilchra, with a heavier shading of 

 brown along the flanks; the yellow of the under parts is duller and 

 more generally suffused with dull orange brown ; the white spots on 

 outer tail feathers are decidedly larger, and the bluish of the dorsal 

 surface is grayer. In the small series examined, difference in size 

 seems to be the most constant character. Following are average meas- 

 urements of the two species : 



