|
Natural HistoryTwo subspecies of Yellow-billed Cuckoo (Coccyzus americanus) are recognized in the western hemisphere: C. a. occidentalis and C. a. americanus. Their range historically extended from southern British Columbia to northern Mexico (Bent 1940). Currently the only known populations of breeding Western Yellow-billed Cuckoos are in California, Arizona, and western New Mexico. Yellow-billed Cuckoos winter in South America from Venezuela to Argentina after a southern migration that extends from August to October (Laymon and Halterman 1985). They migrate north in late June and early July. (DeSchauensee 1970). In California on the Sacramento River, pairs formation begins in late June and is followed by nest building and raising of young (Halterman 1991). Breeding in the Lower Colorado River Valley commences by early July and continues through August with one brood of two or three raised per season. The species is restricted to the mid-summer period for breeding presumably due to a seasonal peak in large insect abundance (Rosenberg et al. 1982). Click on Image for Larger View The pair constructs a flimsy twig nest which is typically 5 to 40 feet above the ground in dense canopy cover. Incubation is primarily by the female, although the male may sit 30% of the time and will occasionally bring food to the female. Both parents attend young and carry food. Young leave the nest at 6 to 8 days post hatching, crawling from branch to branch up to 50 m from the nest. Parental care continues for 3 to 4 weeks after which the southern migration again begins (Halterman 1991). In the southwest, Yellow-billed Cuckoos prefer dense cottonwood/willow stands (Rosenberg et al. 1991, Halterman 1991) although mesquite and salt cedar may be utilized in areas farther east (Hunter et al. 1988). Halterman (1991) reports utilization of riparian patches with low woody vegetation along the Sacramento River in California. Rosenberg et al. (1991) suggest that perhaps the extreme southwestern mid-summer temperatures, which could kill unprotected eggs, may have an effect on this difference in habitat choice, in that mature willows form a sub-canopy layer which provides the best shading of any riparian habitat. Furthermore, standing water in many cottonwood-willow groves may help to lower the air temperature by evaporative cooling. Click
on Image for Larger View
|
|
