LESSER BULLOCK'S ORIOLE 281 



ICTERUS BULLOCKII PARVUS van Rossem 



Lesser Bullock's Oriole 

 HABITS 



Based on the study of a series of 42 adult males and 15 adult 

 females referable to this race, van Rossem (1945) named this subspecies 

 and described it as "similar in color to Icterus bullockii bullockii 

 (Swainson) of western North America in general. Size distinctly 

 smaller. Measurements of the type are: wing, 97; tail, 76; culmen, 

 18.4; tarsus 23.2; middle toe, minus claw, 16.7. The corresponding 

 measurements of Swainson's type of Xanthornus bullockii (examined 

 at Cambridge, England, in 1933, and again on July 4, 1938) are 105, 

 83, 20.0, 24.5, and 17.8 mm. Range. — Coastal slope of California 

 from the San Francisco Bay region south to northern Baja California, 

 and eastward in the extreme southern part of the range to the lower 

 Colorado River valley. Winter range undetermined but occurs in 

 southeastern Arizona and southern Sonora in migration." 



It is of interest to note that Ridgway (1902), in a footnote, called 

 attention long ago to the fact that orioles of this species from Cali- 

 fornia, west of the Sierra Nevada, are smaller than those from the 

 interior to the eastward of that range. 



The observations made by Alden H. Miller (1931) on the song and 

 territorial behavior of two pairs of Bullock's orioles in Contra Costa 

 County, Calif., probably apply to birds of this subspecies. He says 

 that — 



The male Bullock's Oriole arrives on the breeding ground before the female and 

 establishes a singing post, perhaps the entire territory. The females arrive one 

 or two weeks later and come to occupy a territory jointly with a male. The 

 female shares in the defence of territory. * * * The male and female of a pair 

 do not cooperate completely in the defence of territory at least at a time before 

 the nest is built. That is, a female during this period possesses an urge to defend 

 a territory to the exclusion of other females, the male to the exclusion of other 

 males. Other males during or preceding nest building are not repulsed from the 

 territory by the female but instead may be acceptable to the female and may be 

 courted. The converse doubtless is true of the male at other periods in the 

 breeding season. Certainly the male before nest construction is tolerant of two 

 females within his territory. At the beginning of nest construction the females 

 pursue and beg from the males, posturing, fluttering the wings, and singing. At 

 this time the males appear to be passive and consistently move away from the 

 advances of the females. Nevertheless, in flight the males may follow after the 

 females. 



He demonstrated clearly that the females sing more or less regularly 

 during the early part of the nesting period, and gives a chart showing 

 the difference in the songs of the two sexes. 



