Jan., 1918 EARLY AUTUMN BIRDS IN YOSEMITE VALLEY 19 



Rock Wren (Salpinctes obsoletus obsoletus). One seen August 31; heard once or 

 twice afterwards. 



Western House Wren (Troglodytes aedon parkmani). Common but not very num- 

 erous. Last one seen September 15. 



Western Gnatcatcher (Polioptila caerulea obscura). The only one seen was taken 

 September 25. 



Western Bluebird (Sialia mexicana occidentalis). A complete family of Western 

 Bluebirds lived in front of Camp Curry, but the species was seldom noted elsewhere. A 

 small flock, in company with Audubon Warblers, was seen on September 20 near the 

 foot-bridge west of Yosemite Village, but it did not stay long. 



APPROXIMATE DATES OF DEPARTURES 



Black-headed Grosbeak {Zamelodia melanocephala) . None seen after September 20. 



Lazuli Bunting (Passerina amoena). Very scarce toward the end of September, 

 an immature taken September 28. 



Western Warbling Vireo (Vireosylva gilva sicainsoni). Numerous during latter 

 part of August, but disappeared before middle of September. 



Cassin Vireo (Lanivireo solitarius cassini). Numerous at first, gradually growing 

 scarcer, but a few still in valley on September 28. 



California Yellow Warbler (Dendroica aestiva breusteri). Disappeared early in 

 September. 



Golden Pileolated Warbler (Wilsonia pusilla chryseola). Last noticed September 

 22. 



Western House Wren (Troglodytes aedon parkmani) . Last one seen September 15. 



San Francisco, November 1, 1917. 



A NOTE ON THE TRACHEAL AIR-SAC IN THE RUDDY DUCK 



By ALEXANDER WETMORE 



IN A PAPER published recently 1 the writer described a peculiar air-sac in the 

 male Ruddy Duck (Erismatura jamaiccnsis) that was developed from the 

 trachea, and was capable of inflation through a slit behind the larynx until 

 it formed a pronounced swelling on the neck. The dissections on which these ob- 

 servations were based were made in the field in the summer of 1915, and during 

 the following winter. Other observations on this peculiar development were made 

 in the summer of 1916, but through the writer's absence in the field it was found 

 impracticable to include them in the paper quoted, which was then in press. 



On May 29, 1916, and on subsequent dates several adult Ruddy Ducks were 

 captured alive in shallow ponds in the marshes at the mouth of Bear River, 

 Utah. These ducks often were found in narrow channels that, though two feet 

 deep or more, were barely wide enough to allow a boat to pass. As we came down 

 these narrow runs the ducks swam on ahead until finally they came out into 

 ponds where the water was not more than six or eight inches in depth. When 

 closely pressed these birds chose to dive rather than attempt a laborious effort at 

 flight. Under these conditions it was often possible to capture them alive and un- 

 injured. In the clear water they could be seen swimming rapidly, both feet 

 stroking vigorously together, with wings held close at the sides and the head turn- 

 ing quickly as they sought an avenue of escape. 



On examining the males I was surprised to find that normally the tracheal 



1 On Certain Secondary Sexual Characters in the Male Ruddy Duck, Erismatura jaynaicensis (Gmelin). 

 Proc. U. S. Nat. Mus., vol. 52, Feb. 8, 1917, pp. 479-482. 



