Eastern whip-poor-will (Caprimulgus vociferus)
|Also known as:||Whip-poor-will|
|Size||Length: 22 - 26 cm (2)|
|Weight||43 - 64 g (2)|
The eastern whip-poor-will is classified as Least Concern (LC) on the IUCN Red List (1).
An enigmatic and extremely elusive species, the eastern whip-poor-will (Caprimulgus vociferous) has strikingly cryptic plumage. As a result, the whip-poor-will is very rarely seen, making it one of the least studied birds in North America (2) (3) (4). This fairly vocal species is most active at dusk, and on bright, moonlit nights during the breeding season it can be heard producing the characteristic “whip-poor-will” calls for which it is named (4).
The eastern whip-poor-will has a particularly large head, large, flattened eyes, and a small bill with a comparatively wide gape (2). It has mottled or streaked grey, brown and black feathers (3) (4), providing it with excellent camouflage against leaf litter and tree branches in its woodland habitat (4). Broad, blackish stripes mark the crown, and the buff underparts have brown bars which become more solid blackish-brown towards the top of the breast. There is a band of white on the lower part of the throat. The wings of the eastern whip-poor-will are rounded, with greyish-brown wing-coverts that are spotted and speckled in lighter shades of brown (2). The outer three tail feathers of the male have broad white tips, while the tips of the female’s tail feathers are buffy (2) (3).
The whip-poor-will has recently been split from a single species (Caprimulgus vociferous) into two separate species, the eastern whip-poor-will (Caprimulgus vociferus) and the Mexican whip-poor-will (Caprimulgus arizonae), based on differences in their genetics, appearance and vocalisations (2) (5) (6).
The eastern whip-poor-will breeds throughout North America, from Saskatchewan to Nova Scotia and Ontario in southern Canada, and south throughout the United States (1) (4) (6) (7). It also breeds in Honduras (4).
This species winters from north-eastern Mexico and the Gulf Coast of the United States to Central America, including Costa Rica, Panama and Cuba (1) (4) (6) (7).
The eastern whip-poor-will is found in forested or woodland habitats. It requires an open understorey, sparse ground cover or close proximity to other open areas for foraging, while shaded habitats in mixed or deciduous forests are used for roosting and nesting (2) (3) (4) (6) (7).
During the winter, the eastern whip-poor-will occurs in similar habitats to those used during breeding, being found in mixed woods and forests close to clearings and other areas of open ground (3) (4).
Due to its rather secretive behaviour and cryptic colouration, the eastern whip-poor-will remains a relatively unstudied bird, with little known about its behaviour and ecology (2).
The eastern whip-poor-will forages at dusk and dawn and during moonlit periods at night. It typically makes short flights after insects from a perch in a tree or from the ground, and is also known to investigate rotten logs and leaves in search of food. The eastern whip-poor-will has a strictly insectivorous diet, consisting mainly of ants, beetles, flies, grasshoppers, moths and caterpillars (2).
At the start of the breeding season the male whip-poor-will is known to establish a fairly large territory, and from here produces loud, distinctive “whip-poor-will” calls from a variety of perches in an attempt to attract a suitable mate. The timing of breeding varies greatly with location, occurring sometime between late April and early July across most of its range (2).
The eastern whip-poor-will is a ground-nesting species, with the female laying a clutch of two eggs directly among leaf litter on the forest floor (2) (4). The newly laid eggs are cream or greyish-white, and are marbled and dotted with lavender-grey blotches and yellowish-brown or pale brown spots. This colouration fades fairly quickly and the eggs become well camouflaged to match the leaf litter, allowing them to remain undetected by most predators. The eggs are incubated mainly by the female, although sometimes by the male, for around 19 to 21 days, during which time the adult birds remain motionless on or close to the nest throughout much of the day (2).
Hatching of whip-poor-will chicks appears to be closely tied to the lunar cycle, with most young hatching a few days before a full moon. It is thought that this strategy may have developed to allow the adult birds to forage throughout the night during the full moon period, enabling them to catch enough insects to supply the chicks with sufficient energy to grow (2) (3). At around eight days after hatching, the whip-poor-will chicks develop black-speckled feathers to provide them with additional camouflage, after which they move from the nest site into denser cover (2). The male provides much of the care to the chicks after they leave the nest site until they are able to fly at around 20 days old, while the female often lays a second clutch of eggs nearby (2).
Habitat loss is one of the main threats to the eastern whip-poor-will, largely due to the conversion of land for agriculture. Natural succession and changes in forest management practices have also led to a reduction in forest and woodland clearings (2) (4), while increasing urbanisation and development have reduced the amount of suitable breeding and feeding habitat for this bird (2).
Additional threats to the eastern whip-poor-will may include declines in important food resources as a result of pollution and pesticide use (2) (4), as well as increasing mortality from collision with vehicles (2).
There are no known specific conservation measures currently in place to protect populations of the eastern whip-poor-will.
Very little is known about the biology and ecology of the eastern whip-poor-will, and further research into its life history would therefore be extremely beneficial in increasing our understanding of this species and in informing future conservation efforts. Studies are particularly needed on juvenile dispersal, migration, habitat use, food selection and the influence of human activity on eastern whip-poor-will populations (2).
Find out more about the eastern whip-poor-will and its conservation:
BirdLife International - Eastern whip-poor-will:
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- Cryptic colouration: colouration that makes animals difficult to detect against their background, so serving to reduce predation. The colouration may provide camouflage against a background, break up the outline of the body, or both.
- Deciduous forest: forest consisting mainly of deciduous trees, which shed their leaves at the end of the growing season.
- Gape: the base of the beak, where the upper and lower parts join.
- Incubation: the act of incubating eggs, that is, keeping them warm so that development is possible.
- Insectivorous: insect-eating.
- Natural succession: the progressive sequence of changes in vegetation types and animal life within a community that, if allowed to continue, results in the formation of a ‘climax community’ (a mature, stable community in equilibrium with the environment).
- Territory: an area occupied and defended by an animal, a pair of animals or a group.
- Wing-coverts: small feathers which cover the bases of other larger feathers, helping to smooth airflow over the wings.
IUCN Red List (February, 2012)
Cink, C.L. (2002) Eastern whip-poor-will (Caprimulgus vociferus). In: Poole, A. (Ed.) The Birds of North America Online. Cornell Lab of Ornithology, Ithaca. Available at:
Cornell Lab of Ornithology: All About Birds - Eastern whip-poor-will (Caprimulgus vociferus) (February, 2012)
Ontario Ministry of Natural Resources - Eastern whip-poor-will (Caprimulgus vociferus) (February, 2012)
BirdLife International (February, 2012)
- Chesser, R.T., Banks, R.C., Barker, F.K., Cicero, C., Dunn, J.L., Kratter, A.W., Lovette, I.J., Rasmussen, P.C., Remsen Jr, J.L., Rising, J.D., Stotz, D.F. and Winker, K. (2010) Fifty-first supplement to the American Ornithologists’ Union. Checklist of North American Birds. The Auk, 127(3): 726-744.
American Ornithologists’ Union (1998) Check-list of North American Birds. Seventh Edition. The American Ornithologists’ Union, Washington, D.C. Available at: