SIALIA. 581 



back, scapulars, etc.; wings (except coverts) and tail as in 

 adult ; beneath white, the feathers of breast, etc., very broadly- 

 bordered with dark grayish or brownish; a whitish orbital 

 ring. Eggs .82 X -64. Hab. Eastern United States, north to 

 Nova Scotia, Ontario, Manitoba, etc., west to base of Eocky 

 Mountains ; Bermudas (resident). 



766. S. sialis (Linn.). Bluebird. 



c\ Breast, etc., light ochraceous-cinnamon, the sides of neck and (usually) 



malar region similar. 



d\ Above light greenish blue or cerulean-blue (much as in S. arctica), 



the sexes differing as in S. sialis; anal region cinnamon-buff; 



length 6.40-7.10, wing (male) 4.05^.20 (4.10), tail 2.70-2.95 



(2.79), culmen .47-.50 (.49), tarsus .80-.85 (.82). Female: Wing 



3.90, tail 2.55. Hab. Highlands of Mexico, north to southern 



-Arizona 766a. S. sialis azurea (Baird). Azure Bluebird. 1 



d*. Above rich cobalt-blue, varying to ultramarine, like S. sialis; 

 otherwise resembling S. azurea. Male: Wing 4.15-4.35 (4.25), 

 tail 2.80-3.00 (2.93), culmen .50, tarsus .62-.65 (.63). Female : 

 Wing 4.05-4.10, tail 2.70-2.80. Sab. Highlands of Guatemala 

 and Honduras. 



S. sialis guatemalae Eidgw. Guatemala Bluebird. 1 

 b 2 . Throat and belly blue. 



Adult male : Above rich smalt-blue (varying to ultramarine), the back 

 usually with more or less of chestnut (sometimes entirely chestnut, 

 rarely entirely blue 8 ) ; lower parts lighter and duller blue, the breast 

 and sides deep cinnamon-chestnut. (Colors duller and more suf- 

 fused in winter.) Length 6.50-7.12, wing 3.95-4.45 (4.19), tail 2.62- 

 3.05 (2.84), culmen .45-.50 (.48), tarsus .80-.90 (.82). Adult female: 

 Head, neck, and upper parts dull gray, paler on throat, browner on 

 back ; rump, upper tail-coverts, and tail bright blue, the outer web 

 of lateral tail-feather whitish ; wings dull blue ; breast and sides 

 dull light cinnamon ; belly dull grayish ; wing about 4.00, tail 2.50. 

 Young: Not always distinguishable with certainty from correspond- 

 ing stage of S. sialis, except by slenderer bill ; usually darker, how- 

 ever, especially on lower parts, the throat dull grayish and sides 

 tinged with dull dark brown. Eggs .81 X -64. Hab. Western 

 United States, north to British Columbia, east to Eocky Moun- 

 tains, south over table-lands of Mexico. 



767. S. mexicana Swains. Western Bluebird. 



1 Swainson's Sialia azurea, usually quoted for this form, is a complete nomen nudum. The name was first 

 coupled with a description by Professor Baird (Review Am. B. i. July, 1864, 62), who is therefore to be quoted 

 as its authority. 



* S. sialis guatemalm Ridgw., Pr. U. S. Nat. Mus. v. June 5, 1882, 13. 



3 This variation is purely individual, and not at all dependent on locality, as supposed by Mr. Seebohk 

 (Cat. B. Brit. Mus. v. 1881, pp. 331-333). 



