50 MIGRATION, ETC., OF THE MOUNTAIN MOCKINGBIRD 



Thrasher. It was one of the birds discovered by Mr. J. K. 

 Townsend, who, with his some time companion Nuttall, explored 

 the region of the Columbia, bringing many ornithological novel- 

 ties to light. aSTuttall speaks of its pleasant song, which he says 

 resembles that of the Thrasher, and ascribes to it powers of 

 imitation ; but as his statement of such ability has not been 

 since corroborated, we are left to infer that it possesses nothing 

 beyond the flexible modulation of the voice for which all its 

 tribe are famous. He discovered a nest, situated in a worm- 

 wood-bush, containing four eggs. The original accounts of the 

 species constituted the sum of our information respecting it 

 for many years, until the general opening-up of almost untrod- 

 den wastes put other eager and curious observers upon its track. 

 From what we have learned, it would appear to have been mis- 

 named the Mountain Mockingbird, since, as has been intimated, 

 its repertoire is not remarkably extensive, while its favorite 

 haunts are the arid and desolate sage plains of the great cen- 

 tral plateau. We are now pretty well acquainted with its 

 geographical distribution, though more precise knowledge of 

 its movements would be acceptable. It is migratory, like most 

 of its tribe, but only within a limited area. It is known to be 

 resident in Texas, where my friend H. E. Dresser, of London, 

 observed it at San Antonio and Eagle Pass in winter and sum- 

 mer, and where he procured the eggs. He found it, like others, 

 in brushy plains, and noticed its terrestrial habits. As well as 

 I can judge from the accounts to which I have referred for in- 

 formation having nothing original to present upon the subject 

 the bird offers one of the many instances of what I should call 

 " migration at will", if I dared to propose a sort of paradoxical 

 term. That is to say : out of the sum-total of individuals com- 

 posing the species, congregated in their winter haunts, a cer- 

 tain percentage elects to go north in the spring, dropping loi- 

 terers by the way, while the rest breed where they wintered. 

 In this manner, the species spreads latitudinally until the limit 

 of its dispersion, which cannot be far from the northern bound- 

 ary of the United States, is reached, and may be found nesting 

 anywhere within the area it inhabits. In the fall the return 

 movement is accomplished, and the species is then withdrawn 

 into its comparatively narrow winter quarters, the limits of 

 which I believe remain to be ascertained. This kind of optional 

 or elective migration, witnessed in many other cases besides 

 the present one, contrasts with the regular migration perforce 



