BENT'S CROSSBILL 523 



of molt, rather than on the dietary deficiencies usually held respon- 

 sible for pigment aberrations in captive birds. Age variation in size 

 was demonstrated; this variation is of sufficient magnitude to influence 

 taxonomic studies and is partially masked by the similarity in plumage 

 of first winter males and adult males in benti. 



Behavior. — H. B. Tordoff (1954) made intensive studies of captive 

 birds. Their resemblance to cones protects them as they roost, far 

 out on the ends of coniferous branches. Before going to sleep birds 

 extend and retract their tongues, three to five times a second, for as 

 many seconds. After a pause, they repeat the process. The tongue 

 may project on either side of the mandibles, and it extends well 

 beyond the tips. Sizable clusters of white frothy bubbles appear at 

 the ends of the bills. These clusters soon break, leaving the mandibles 

 wet and shining. Coincident with the tongue action the birds open 

 and close their bills, but at a slower rate. Also, they close the bill in 

 the "wrong" direction, resulting in a peculiar appearance because the 

 mouth will not close evenly. It is possible that this procedure brings 

 about a wearing down of the nonoccluding edges of the bill by abra- 

 sion, with the moisture acting like water on a whetstone. Birds are 

 either right-handed of left-handed in opening cones, according to 

 which way the mandibles are crossed. In feeding, the birds carry 

 pine cones with their bills to a perch, hold the cones with their feet, 

 and insert the tips of the open mandibles. With the long axis of the 

 bird's head approximately at right angles to the long axis of the cone, 

 the tip of the lower mandible presses towards the central axis of the 

 cone and raises a scale against the essentially stationary tip of the 

 upper mandible. The tongue then probes and removes the seeds. 

 There is a peck order of males, another of females, and a dominance of 

 males over females. 



Bathing and sun-bathing activities are customarily social. Upon 

 seeing hawks which are barely visible to the human eye the birds 

 become motionless, uttering a single note, tuck, tuck, tuck, but 

 resume activities a minute or so after the hawk has passed. 



Distribution 



Range. — Chiefly the Rocky Mountain states. 



Breeding range. — Bent's crossbill breeds, and is largely resident, 

 from southeastern Montana (Powder Eiver County), northeastern 

 Wyoming (Weston and Crook counties), and western South Dakota 

 (Harding County, Black Hills) south to eastern Utah (Uinta Moun- 

 tains, Cedar Breaks; intergrading area between grinnelli and benti), 

 southeastern Colorado (La Plata County, Fort Garland), and northern 

 New Mexico (Chama). 



