8 



BULLETIN OF THE NUTTALL 



ON GEOGRAPHICAL VARIATION IN TURDUS ' 

 MIGRATORIUS. 



BY ROBERT EIDGWAY. 



Certain diflferences between Eastern specimens of the common 

 Robin and those from the Rocky Mountains were first pointed out 

 by Professor Baird, in his "Review of American Birds" (1864, 

 pp. 28, 29), in the following words : " In highly plumaged speci- 

 mens from the East the feathers of the interscapular region are 

 frequently, even generally, tinged with blackish in their centres, 

 passing gi-adually into ash on the edges, and the black of the head 

 ceas3s to be abruptly defined. There is also usually a well-defined 

 whitish tip, half an inch long, to the outer tail-feathers. In Rocky 

 Mountain skins the tail is either black, except a very narrow 

 whitish edge, or the white tips of Eastern specimens are replaced 

 by a dull gray. The black of the head, too, is better defined, the 

 interscapular feathers more uniformly ash, and the vipper parts 

 without the faint brownish wash so frequently seen in Eastern 

 specimens. There are, however, some exceptions to these features 

 in sjiecimens from each locality. The colors generally of Western 

 birds appear to be paler." Again, in the "History of North 

 American Birds" (Vol. I, p. 25), the same and additional differen- 

 ces are alluded to, as follows : " There are some variations, both 

 of color and proportions, between Eastern and Western speci- 

 mens of the Robin. In the latter there is a tendency to a 

 longer tail, though the difference is not marked ; and, as a rule, 

 they slightly exceed Eastern specimens in size. The broad white 

 tip to the lateral tail-feather — so conspicuous a mark of Eastern 

 birds — is scarcely to be found at all in any Western ones ; and in 

 the latter the black of the head is very sharply defined against the 

 lighter, clearer ash of the back, there liardly ever being a tendency 

 in it to continue backward in the form of central spots to the 

 feathers, as is almost constantly seen in Eastern examples ; of 

 Western specimens, the rufous, too, is appreciably lighter than in 

 Eastern." 



Very extensive material received at the National Museum since 

 the above was written tends to confirm the constancy of most of 

 these differences between Eastern and Western Robins, while other 



ORNITHOLOGICAL CLUB. 



9 



points of diversity, previously overlooked, have been detected, the 

 most important being the much blacker tail of Eastern birds, and 

 their decidedly shorter wing. 



Upon the whole, the two forms seem to constitute two veiy 

 strongly marked geographical races, which may be distinguished as 

 follows : — 



T. mifjratorins. — Wing, 4.85-5.35 ; tail, 4.10-4.60 ; bill, from nos- 

 tril, .48 -.51 ; tarsus, 1.20-1.35 ; middle toe, .85 -.92.* Inner web of 

 outer tail-featlier with a distinct white terminal spot. Tail-feathers of 

 adult male dusky black, with slight edging of plunibeus. Habitat. 

 Eastern region, including the whole of Alaska, Eastern Mexico, and the 

 eastern border of the Missouri Plains. 



T. propinquus, Ridgw. (MSS.). — Wing, 5.35 - 5.60 ; tail, 4.60 - 4.70 ; 

 bill, from nostril, .50 -.55 ; tarsus, 1.30-1.35 ; middle toe, .90. Inner 

 web of lateral tail-feather with merely a narrower terminal edging of white, 

 or with no white whatever. Tail-feathers of adult male dusky slate, with- 

 out distinctl}' paler edges. Habitat. Western region, including eastern 

 base of Rocky Mountains. 



We find the character of blackish centres to the interscapulars in 

 Eastern specimens to be too inconstant a feature to serve as a 

 character. No specimens of the Western series are so marked, but 

 many Eastern ones, otherwise typical, have no trace of these mark- 

 ings. It is a well-known fact that the eggs of the Western Robins 

 average considerably larger in size than those of Eastern birds. 



Buli. N.O.O. 2. Jaa.,1877.p. 



* 



