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Editor’s Note: Eastern (vociferous group) and Western (now "Mexican"; arizonae group) Whip-Poor-Wills have recently been separated on the basis of differences in vocalizations and mitochondrial and nuclear DNA, as well as in morphology and egg pigmentation. See the 51st Supplement to the American Ornithologists’ Union Checklist of North American Birds for details. Future revisions of this account will reflect this change.Editor's Note #2: Phylogenic analysis of nuclear and mitochondrial DNA has shown the genus Caprimulgus is highly polyphyletic and that the linear sequence of species placed in that genus does not reflect their evolutionary relationships. As a result, the genus Antrostomus is restored for this species, and others in Caprimulgus. Future revisions of this account will reflect these changes.
More frequently heard than seen, the Whip-poor-will remains an elusive species even for seasoned field ornithologists. Its breeding range is fairly well known, due in large part to records of singing males on territories, but there are few nest records. The first documented nest of this species for Oklahoma was recorded in 1980 (Wood 1982) and for South Dakota in 1994 (Dean et al. 1995)! This is a beautifully cryptic bird, but its well-camouflaged eggs and young, its crepuscular or nocturnal foraging and breeding behavior, and its large woodland territories have made it one of the least-studied members of the North American avifauna.
A ground-nesting species, the Whip-poor-will lays its clutch of 2 eggs directly on leaf litter of the forest floor. Adults remain motionless on the nest or on a roost site during daylight hours and become active only at dusk. Whip-poor-wills usually forage only at dawn or dusk, but on moonlit nights catch moths and beetles all night long. Hatching of chicks seems to be closely tied to periods of full moon so the parents can supply the extra energy demands of their rapidly growing brood. Females do most of the incubating and brooding, but the male participates as well. Young are fed regurgitated insects and can move from the nest site within days of hatching if disturbed. When the young molt into their black-speckled, highly camouflaged feathers at the age of about 8 days, the female often leaves them in the care of the male and begins a new clutch of 2 eggs a short distance away within the territory.
Much of the biology of the Whip-poor-will remains unstudied, largely due to its nocturnal activity and cryptic behavior and plumage. What we do know about its behavior, physiology, and ecology is often anecdotal, at best. Information, however, from New York, Ontario, Quebec, and Iowa on breeding biology of single pairs (Mousley 1937, Raynor 1941, Fowle and Fowle 1954, Kent and Vane 1958) has helped define nest sites, behavior during incubation and brooding, development of young, and vocalizations. More recent studies in Ontario using radiotelemetry with slightly larger samples have provided information on timing of breeding in relation to the lunar cycle and on the inability of Whip-poor-wills to make use of torpor in inclement weather (Mills 1986, Hickey 1993). Continuing studies of a marked population in Kansas provide important data on demography (Cink in press c). This interesting species deserves more detailed study.