636 U.S. NATIONAL MUSEUM BULLETIN 23 7 pabt 2 



their presence in an area owing to their habit of calling frequently 

 under most conditions. As indicated above, they are not strictly 

 confined to riparian vegetation, but will venture forth a few yards 

 into adjacent, more open situations to forage and dust bathe. When 

 disturbed, they usually retreat directly back into riparian growth, 

 even though closer shelter may be available. 



Abert's towhees live in areas marked by very hot summers ; environ- 

 mental temperatures above 40° C. and intense solar radiation are 

 common. During hot weather these birds generally confine their 

 activity to the cooler parts of the day — the early morning and late 

 afternoon. In the hottest part of the day, between approximately 

 11:00 a.m. and 3:30 p.m., they apparently take shelter in the densest 

 part of their riparian habitat and remain inactive. Along the Alamo 

 River, Imperial County, Calif., I (1954) never found them in open areas 

 during mid-day in hot weather. This pattern of behavior, which 

 minimizes their metabolic heat production in the coolest surroundings 

 available, appears to be of critical importance in their coping with heat 

 stress. Activity of Abert's towhees declined to a much smaller degree 

 dm^ing the middle of the day in cooler weather, when birds were 

 observed frequently in the more open parts of their habitat. 



Various opinions have been expressed concerning the social tenden- 

 cies of these birds. Bendire (1890), on the basis of experience with 

 P. a. aberti, considered them to be less social than brown towhees 

 (P. f. mesoleucus), whereas Coues (1866), on the basis of experience 

 with the same form, thought them to be more gregarious than other 

 members of the genus Pipilo. Coues, according to Baird, Brewer, 

 and Ridgway (1874b), observed small flocks of this form in September. 

 Henshaw (1875) also observed them to be gregarious in this month. 

 Coues (1866) noted Abert's towhees to associate occasionally with 

 brown towhees along Rillito Creek in Arizona. I have always con- 

 sidered Abert's towhees to be rather gregarious during the nonbreeding 

 season, and this is consistent with the observations of Brown (1903), 

 who repeatedly saw them in rather large flocks in the early winter 

 months along the Colorado and lower Gila rivers "scratching in 

 the earth and sunning themselves like a lot of quail." 



In the vicinity of Tucson, Arizona, P. a. aberti and P. juscus 

 mesoleucus occur together in the same mesquite river-bottom wood- 

 lands. J. T. Marshall (1960) considers that they are in direct 

 competition with each other there, though he found little indication 

 of antagonism between the two species. 



Voice. — The call of the Abert's towhee is reminiscent of that of the 

 brown towhee, but it seems to me to be less metallic and to have 

 a more whistlelike quality. It has been variously described as "sharp, 

 high pitched" (F. M. Bailey, 1928); a "loud, clear, sharp chirp" 



