Common poorwills range throughout western North America from south central British Columbia and southwestern Saskatchewan to central Mexico. Northern populations migrate to the southern portions of their range, from California, Arizona, and Texas to central Mexico, from September to November and return April to May. This migration may vary by a month depending upon weather conditions and the portion of the breeding range occupied. Southern populations arrive for breeding season from February to March and leave October to November for their winter range. Some southern populations occupy the same region year round but migrate to higher elevations for the breeding season and to lower elevations during the winter. (Alderfer, 2006; Csada and Brigham, 1992; Dunne, 2006)
Common poorwills are found in dry, open areas in diverse habitats such as grasslands, forest, hills, and deserts. Vegetation varies, with preference given to short grasses and shrubs or open forest in areas with deciduous or coniferous growth. Trees or shrubs reported in proximity to nesting and roosting areas include, but are not limited to, such species as white fir, ponderosa pine, trembling aspen, Jeffrey pine and creosote. Roost sites are chosen for proximity to bare ground, vegetative debris, and are usually open with little live vegetation cover. Common poorwills typically nest at elevations between 500 to 1000 meters, with some found over 2500 meters. (Csada and Brigham, 1992; Dunne, 2006; Hardy, et al., 1998; Wang and Brigham, 1997)
Common poorwills are medium-sized birds with an adult length of 19 to 21 cm. The average mass within a sample ofin British Columbia was 47.2 +/- 6.0 grams for males and 49.5 +/- 6.3 grams for females. Average wing span in that sample was 42.7 cm for males and 44.1 cm for females. Weight ranges vary among populations and with the time of year. Males lose weight early in the breeding season and both sexes gain weight prior to migration. The size of males and females is similar with females tending towards slightly larger average measurements than males.
Overall color ranges from mottled brown and white to mottled black and white patterns. The ventral side is grey-white with thin charcoal lateral bands progressing to a dark band at the throat. The dorsal surface has cryptic mottled pattern in grey, black, and brown shades and the lateral tail feathers have black and brown bands with white or dun colored tips. The wings are sandy and brown barred at the dorsolateral trailing side and mottled on the medial leading edge. The beak has a ventral curve, is short and wide, and has large open gape with pronounced bristles extending laterally from base.
The species can be distinguished from other members of the Caprimulgidae family in North America by a thicker white throat patch and short tail length. The wingtips extend to the end of the tail when folded, and a large head appears to transition to body without a neck, giving them a stout appearance. The other members of this family have a longer tail extending past the wingtip and do not have the typical lateral white or buff coloured rectrices found in common poorwills. Males and females are relatively monomorphic with only small distinguishing characteristics such as white tipped rectrix feathers for males and buff for the females. Juveniles have similar appearance to adults as well.
Common poorwills are polytypic, with five described subspecies based in large part upon geography even though the winter ranges appear to overlap. However, the existence of subspecies is debatable without additional genetic research. In addition, light and dark morphs exist throughout the range making differentiation, based upon appearance, between subspecies and morphs difficult. (Alderfer, 2006; Csada and Brigham, 1992; Csada and Brigham, 1994; Dunne, 2006; Thomas, et al., 1996)
Male common poorwills establish a territory upon return to their breeding area in the spring and actively defend the territory against other males. Energy expenditure for males for calling and territory defense has been measured to be 5.1 time the usual basal metabolic rate. This means that males have one of the highest energy expenditure rates relative to basal metabolic rates when breeding as compared to other birds (>95% of other species). Females do not have similarly high levels and the field metabolic rate for males decreases over summer to near that of females by the time of the second brood.
There is no distinguishing characteristic between mating calls and songs in male common poorwills and similar vocalizations have also been reported for females. The song consists of a three note poor-will-ow sound in the 1.5 khz range. The calling frequency for males is much higher during the start of breeding season and occurs from evening through the night to dawn while on low perches or the ground.
It is not known if the arrival of males coincides with the arrival of females for the start of breeding season. There has been suggestion that males and females return to the same areas over consecutive seasons in northernmost populations, but further research is required. Also, pairs are monogamous over a single breeding season. Very little is known about common poorwill mate selection and reproductive behavior due primarily to their nocturnal activity. (Csada and Brigham, 1992; Csada and Brigham, 1994; Hardy, et al., 1998; Mengel, et al., 1972; Thomas, et al., 1996)
Common poorwill pairs typically lay the first eggs soon after arrival in their breeding range in late May to June in Canadian populations. A second clutch is laid July to August in a nest approximately 100 meters from the first and the male has been reported to continue feeding the young from the first clutch even as the female incubates the second. Incubation duties are shared between males and females. There are typically two buff colored eggs per clutch laid over two consecutive days and each clutch is incubated for 20 to 21 days. Mass at hatching is reported to be about 4 grams. Nestlings are cared for a period of 20 to 22 days after hatching until they have fledged and first flight, indicating independence, is at 20 to 23 days. Nesting sites are usually on the ground in small open areas that have some shelter provided by nearby low objects such as rocks, shrubs or fallen trees. No nests are built, other than small shallow depressions on the ground. Eggs and nestlings are moved short distances of 1 to 3 meters every couple of days for thermoregulation or in response to disturbance by intruders. The age of sexual maturity for common poorwills is not known.
A remarkable aspect of incubation and brooding is the ability of the parent to enter into torpor in response to inclement weather. Parents in torpor with cloacal temperatures as low as 11.5 degrees Celsius have been discovered incubating eggs. However, even though this adaptation saves parental energy, it has the consequence of reducing egg viability and results in higher rates of nest abandonment. (Aldrich, 1935; Csada and Brigham, 1992; Csada and Brigham, 1994; Kissner and Brigham, 1993; Orr, 1948; Swenson and Hendricks, 1983)
Both common poorwill parents share incubation duties until hatching. The timing of and amount of care each parent provides for eggs or nestlings differs between pairs. The male is more likely to incubate eggs during the day. After hatching, females are more likely to brood nestlings during daytime. The parent brooding or incubating during the day is not relieved until evening and then eggs or nestlings may be left for short periods during nocturnal hours while the parents hunt. The behavior of limiting daylight movement and relying on camouflage presumably helps protects against predators active during daylight. Parents remain still during nesting until a person or predator approaches within a distance of 1 meter. At that point, the parent will usually flush from the nest. They may also make hissing or growling noises, fluff their feathers, or elevate their wings in attempt to intimidate intruders, while staying put on the nest. Parents may attempt to distract predators from the nesting site by landing close by after flushing and calling. The nestlings are fed a diet of regurgitated insects until they have fledged. Association of the first clutch with the parents until the hatching of the second clutch has been reported, but may not be typical for the species. (Aldrich, 1935; Csada and Brigham, 1992; Csada and Brigham, 1994; Kissner and Brigham, 1993; Orr, 1948)
Common poorwill lifespan in captivity is not available in the literature, as the species does not adapt well to human care. There is limited information on longevity in the wild. Several banded individuals were captured over two consecutive seasons (Csada and Brigham, 1994). As well,the same individual returned to a hibernation site over 3 winters before disappearing (Jaeger, 1949). The longest lifespan, recorded in literature, for an individual in the wild is therefore at least three years. (Csada and Brigham, 1994; Jaeger, 1949)
Common poorwills are an awkward on the ground and typically land close to their nest. Flight is close to the ground and is described as several moth-like flutters followed by a glide. Theyl usually roost on the ground or on low hanging limbs during daytime and occasionally individuals may be found roosting together. Roost sites are almost always changed on a daily basis. The parent not brooding or incubating eggs or hatchlings will roost at sites away from the nesting area.
Common poorwills preen themselves with the help of a pectinated comb on the middle claw that may assist with parasite removal. They also dust bathe. Behavior noted in captive and wild common poorwills is a rocking movement for 3 to 15 seconds prior to initiating scratching or preening. They have been observed holding their wings in a vertical position after landing for 5 to 10 seconds before snapping back into folded position and remaining still. The reason for these last two behaviors are not clear. (Brauner, 1953; Csada and Brigham, 1992; Hardy, et al., 1998; Wang and Brigham, 1997)
Northern populations of common poorwills have lower population densities than southern populations. Territories are separated by approximately 500 meters in northern populations in British Columbia and Saskatchewan and have population densities of 0.13 birds per survey station. Population densities are higher at Arizona sites, with 0.43 to 0.49 birds per survey station. (Csada and Brigham, 1992; Csada and Brigham, 1994; Hardy, et al., 1998)
Common poorwills appear to primarily communicate using songs or calls. The same vocalization for mating is also used for communication. Both sexes make the same call, poor-will-ow in the 1.5 kHz range. The call is made year round, although frequency and duration of calling increases among males during mating season. The song is used by males to advertise their presence in a territory and to attract females. Recorded common poorwill calls played in a territory will attract the male. Wing clapping has been reported in one instance (Mengel, Sharpe and Woolfenden, 1972), but whether it is used for courtship or territorial defense has not yet been established.
Common poorwills have large eyes suited for seeing in low light conditions and from positions on ground or on low perches. Vision and hearing are thus the two primary senses used by this species to assess surroundings. (Brauner, 1953; Csada and Brigham, 1992; Mengel, et al., 1972)
Common poorwills are insectivorous, with a diet consisting largely of night flying beetles (Coleoptera) and moths (Lepidoptera). Other insect orders do not exceed 10 % of the diet, as determined by analysis of fecal pellets. Prey appear to be selected for size with minimum lengths of 5 to 7 mm. This selectivity may maximize the energy obtained from food sources or it may represent the lower limit of the insects that can be visually detected in low light conditions. One study estimated that common poorwills make 200 to 300 flights per night to obtain a minimum of 9.7 g of insects to maintain weight during the breeding season. Hunting is in low light conditions from dusk to dawn. There appears to be a minimum amount of light required, as hunting activity increases during moonlight nights compared to dark nights. Common poorwills use an ambush hunting style, as they prefer to wait on the ground or low perch and fly almost vertically upwards to a maximum of 3 meters once a desired insect has been spotted. Long flights for foraging are rare and most last about three seconds before they return to the ground. Large eyes adapted for low light conditions and a large gaping mouth for prey capture are adaptations that enhance this hunting style. (Bayne and Brigham, 1995; Brauner, 1953; Brigham and Barclay, 1992; Csada and Brigham, 1992; Csada, et al., 1992; Thomas, et al., 1996)
Common poorwills have several behavioral adaptations to minimize predation. These include nocturnal activity to avoid most daytime predators and sitting still when roosting or when on the nest, to prevent movement from being detected. Incubating parents may attempt to lead intruders away from the nest by feigning injury and landing close by to the nest once flushed. Moving the eggs and nestlings also helps prevent detection by predators since the buildup of fecal matter reveals their presence to some predators. In addition, their cryptic coloration makes them difficult to detect. Common poorwill may limit their calling when they hear calls by predatory nocturnal animals like owls. Nonetheless, losses due to predation can be high and numerous species are recorded or are strongly suspected to be predators of (Csada and Brigham, 1992; Csada and Brigham, 1994; Orr, 1948; Wang, et al., 1995; Woods and Brigham, 2008). These include, but are not limited to, northern harriers, great horned owls, western screech-owls coyotes, badgers, foxes, skunks, rattlesnakes, and gopher snakes.
It is not known whether common poorwills have mutualistic relationships with other species. However, they serve as hosts for at least two species of parasites. Lice (Ethiopterum macrocephalum) has been found infesting the crown and nape of a common poorwill and mites (Ptilonyssus niitzchi) have been found in the nasal passages. Common poorwills have further roles as both predators of nocturnal insects and as prey for carnivorous mammals, snakes, owls, and hawks. (Bayne and Brigham, 1995; Brauner, 1953; Csada and Brigham, 1992; Wang, et al., 1995)
Common poorwills prey on nocturnal insects such as moths and beetles. No research has been done regarding the specific insect species that they prey on, but presumably some are pests of agriculture and forestry.
Of great interest to scientists is the ability of common poorwills to go into torpor in response to environmental stress, such as decreased food sources or inclement weather. Numerous studies have been done investigating this phenomenon. The lack of mitochondrial uncoupling proteins in their adipose tissues, suggests convergent evolution to a similar characteristic found in hibernating bats. (Bayne and Brigham, 1995; Brigham and Trayhurn, 1994; Csada, et al., 1992)
Common poorwills are listed as an IUCN species of least concern and are not listed in the CITES appendices. Although populations are presumed to migrate from Canada and the United States to Mexico, they are not be protected under the United States Migratory Bird Treaty Act. Populations are presumed to be large, although the distribution may be somewhat fragmented. They may benefit from human activities such as cattle grazing or logging, as they create open habitats. (Csada and Brigham, 1992)
Common poorwills were the first bird discovered to hibernate under natural conditions, with one individual remaining in torpor for at least 85 days for the 1947 to 1948 season (Jaeger, 1949). This has been confirmed with many laboratory studies of torpor in this species. Torpor is induced in captive specimens by withholding food and decreasing the ambient temperature. Metabolism slows down in response, as measured by decreased respiratory and heart rates, and the bird enters torpor with body temperature closely following that of the environment. As the ambient temperature increases to 15 to 19 degrees Celsius, they come out of torpor and become active once again (Howell and Bartholomew, 1959). Later study on torpor by Withers (1977) demonstrated arousal from torpor at temperatures as low as 10 degrees Celsius. (Howell and Bartholomew, 1959; Jaeger, 1949; Withers, 1977)
Common poorwills live in climates with extreme temperature variance, including desert, throughout their range. The behavior of sitting still while roosting or on ground nests throughout the day during summer means that this species has adaptations to survive extreme heat. They are able to dissipate heat efficiently by panting (its large mouth is heavily capillarized to act as a radiator) and increasing rates of cutaneous water loss. They can handle body temperatures as high at 43.5°C and maintain a body temperature of 42°C even when ambient temperatures are at 48°C. The explanation for this ability is suggested to be a low basal metabolic rate which would reduce reliance on water loss for cooling. (Bartholomew, et al., 1962; Csada and Brigham, 1992)
Noel Ives (author), University of Alberta, Augustana Campus, Doris Audet (editor), University of Alberta, Augustana Campus, Tanya Dewey (editor), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.
uses smells or other chemicals to communicate
active at dawn and dusk
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
An animal that eats mainly insects or spiders.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
parental care is carried out by males
makes seasonal movements between breeding and wintering grounds
Having one mate at a time.
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.
scrub forests develop in areas that experience dry seasons.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
uses sight to communicate
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Brigham, R., R. Barclay. 1992. Lunar influence on foraging and nesting activity of common poorwills (Phalaenoptilus nuttallii). The Auk, 109/2: 315-320.
Brigham, R., P. Trayhurn. 1994. Brown fat in birds? A test for the mamalian bat-specific mitochondrial uncoupling protein in common poorwills. The Condor, 96: 208-211.
Csada, R., R. Brigham. 1994. Breeding biology of the common poorwill at the northern edge of its distribution. Journal of Field Ornithology, 65/2: 186-193.
Csada, R., R. Brigham. 1992. Phalaenoptilus nuttalli: Common poorwill. Birds of North America, 32: 1-13.
Csada, R., R. Brigham, B. Pittendrigh. 1992. Prey Selection in relation to insect availability by the common poorwill. Canadian Journal of Zoology, 70/7: 1299-1303.
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Hardy, P., T. Abeloe, R. Barry, M. Morrison. 1998. Abundance and habitat associations of common poorwills in the sonoran desert. The Southwestern Naturalist, 43/2: 234-241.
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Jaeger, E. 1949. The Condor. Further observations on the hibernation of the poor-will, 51/3: 105-109.
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Orr, R. 1948. Nesting behavior of the poor-will. The Auk, 65/1: 46-54.
Swenson, J., P. Hendricks. 1983. Chick movements in common poorwills. The Wilson Bulletin, 95/2: 309-310.
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Wang, K., R. Brigham. 1997. Roost-site characteristics of common poorwills, Phalaenoptilus nuttallii, in Saskatchewan. Canadian Field Naturalist, 111/4: 543-547.
Wang, K., M. Kalcounis, D. Bender, D. Gummer, R. Brigham. 1995. Predation on free-ranging common poorwills in Saskatchewan. Journal of Field Ornithology, 66/3: 400-403.
Withers, P. 1977. Respiration, metabolism, and heat exchange of euthermic and torpid poorwills and hummingbirds.. Physiological Zoology, 50/1: 43-52.
Woods, C., R. Brigham. 2008. Common poorwill activity and calling behavior in relation to moonlight and predation. The Wilson Journal of Ornithology, 120/3: 505-512.