FAMILY TYRANNIDAE 449 



Measurements. — Males (10 from United States, Canada, and 

 Alaska), wing 102.1-114.1 (107.2), tail 63.3-74.4 (69.1). culmen 

 from base 17.0-18.5 (17.4). tarsus 14.5-15.5 (15.0) mm. 



Females (10 from United States, Canada, and Alaska), wing 99.1- 

 106.0 (102.6). tail 63.0-71.3 (66.3), culmen from base 16.5-17.9 

 (16.8), tarsus 14.0-15.5 (14.8) mm. 



Size in this species is variable, with part of those of the western 

 half of the continent averaging slightly larger. It was once suggested 

 that two populations were indicated but with increase in information 

 the supposed differences proved to be indefinite. 



Fairly common passage migrant to and from wintering grounds 

 in South America, with a few remaining through the period of 

 winter. Found from sea level to the higher mountains. 



They are widely distributed, found singly wherever there are trees, 

 from mountain forests to the borders of lowland fields and the vicinity 

 of houses. High perches from which the view is unobstructed are the 

 usual choice as is their custom in their northern summer homes. 

 Customarily they are silent, but they may call at times, especially 

 during the passage northward in spring. 



From records assembled from a number of sources, mainly sight 

 records through Dr. Eisenmann, passage southward comes between 

 August 29 and November 18, with return from March 9 to May 30. 

 Most move through September and October, and April and May. 

 A record at the head of the Rio Guabal in northern Code on Febru- 

 ary 28, 1962, indicates a wintering individual, as does one taken at 

 El Volcan, February 17. 1960, in which the two outermost primaries 

 in both wings were in molt. From February 23 to 29, 1964, on Cerro 

 Mali, Darien, one passed its days in tall trees on a narrow ridge where 

 a clearing had been cut to allow access by helicopters. At sunset this 

 bird came lower to dead stubs on the slope adjacent to our camp. 

 Here, while it made an occasional sally for insects, it seemed nervous 

 as it continually twisted the head about and jerked, raised, and 

 lowered its tail. This nightly performance terminated at dusk when 

 finally it darted quickly into the leafy tree crown in the high forest 

 behind our rancho. I wondered if its obvious nervousness was fear 

 that an owl might await in the cover that it sought for shelter during 

 sleep. 



CONTOPUS LUGUBRIS Lawrence: Dark Pewee, Mosquero . 



Oscuro 



Contoptis higiihris Lawrence, Ann. Lye. Nat. Hist. New York, vol. 8, May 

 1865, p. 134. (Barranca, Costa Rica.) 



