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.
Mating System: monogamous
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.
Breeding interval: Common poorwills breed twice per year.
Breeding season: Common poorwill breeding sually occurs May to September.
Average eggs per season: 4.
Range time to hatching: 20 to 21 days.
Average birth mass: 4 g.
Range fledging age: 20 to 22 days.
Range time to independence: 20 to 23 days.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)
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.
Parental Investment: altricial ; male parental care ; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); post-independence association with parents