Skip booklet index and go to page content

COSEWIC Assessment and Status Report on the Common Nighthawk in Canada

Biology

Reproduction

The age of sexual maturity for this species is one year (Poulin et al. 1996). The two eggs are laid directly on soil, sand, gravel or bare rock (Dexter, 1952; Weller, 1958; Peck and James, 1983; Poulin et al. 1996; Sinclair et al. 2003). The species generally has one brood per year, but a second clutch may be produced in the southern part of its range (Weller, 1958). The eggs are generally laid from the second week of May to mid-August (Gauthier and Aubry, 1996; Poulin et al. 1996). Only the female incubates the eggs, for an incubation period of 16 to 20 days, depending on the region (Rust, 1947; Foyle, 1946; Campbell et al. 1990). Nestlings generally remain in the nest from mid-June to late August (Poulin et al. 1996). During this period, the female broods the nestlings continually and the male feeds the female and the nestlings in the nest (Granza, 1967; Brigham, 1989). The nestlings are semi-precocial and are able to move short distances in search of shade within the first few days (Gross, 1940). The young begin to fly after 18 days and can capture their first insects near the ground after 25 to 30 days, (Gross, 1940; Rust, 1947). The nestlings reach full development at between 45 and 52 days (Gross, 1940; Rust, 1947). In Quebec, the period of dependency after leaving the nest has been estimated to be from the second week of June to the last week of July (Gauthier and Aubry, 1996). In the Yukon, juveniles still dependent on adults and not yet able to sustain flight over large distances were reported as late as 22nd August (Sinclair et al. 2003).


Survival

Very little information is available on annual adult survival rates on breeding or wintering grounds. Moreover, no studies have been conducted on reproductive success or fledgling survival rates (Poulin et al. 1996). The life span of the Common Nighthawk is generally 4-5 years (Poulin et al. 1996), although banded birds aged 9 years have been reported (Dexter, 1961). Similarly, extremely high temperatures on roof surfaces in summer (i.e. 60 °C) can cause nestling mortality (Gross, 1940).


Dispersal/Migration

The Common Nighthawk has one of the longest north-south migration distances of any species in North America (Poulin et al. 1996). Nighthawks arrive in Canada from early May to the beginning of June (Weir, 1989; Manitoba Avian Research Committee, 2003) and migration to South America occurs from mid-August to mid-September (Ouellet, 1974; Manitoba Avian Research Committee, 2003). These autumnal migratory flights are often associated with the emergence of flying ants (hymenoptera) in August (Poulin et al. 1996) and involve flocks ranging from 10 to an estimated 16 000 individuals (Ouellet, 1974; Tuft, 1986; Weir, 1989; Poulin et al. 1996).

Factors affecting dispersal from the natal site are unknown (Poulin et al. 1996).  Studies involving banded birds have found that female nighthawks exhibit nest site fidelity (Dexter, 1961; Poulin et al. 1996). No data are available for males (Poulin et al. 1996).


Diet and Feeding Habits

The Common Nighthawk is an aerial insectivore that feeds primarily at dusk and dawn (Poulin et al. 1996) at heights varying from 1 m to more than 80 m (Brigham, 1990; Poulin et al. 1996). Unlike other species of nightjar which use echolocation, the Common Nighthawk visually detects its prey, aided by a highly developed tapetum lucidum, which improves its vision in low-light environments (Poulin et al. 1996). Where insect densities are high, the species can feed in groups ranging from a few dozen to several hundred individuals (Brigham and Fenton, 1991; Brigham and Barclay, 1995). In urban areas, nighthawks often forage near street and building lights, where they capture insects attracted by the light (Poulin et al. 1996). During breeding and migration periods, the species is regularly seen feeding on trichoptera over water (Montreal, Ouellet, 1974; Okanagan Valley, Firman et al. 1993; northwestern Saskatchewan, C. Savignac, pers. obs. 2005).

The diet of the Common Nighthawk includes a wide variety of insects (over 50 species), with the species showing a preference for homoptera, coleoptera, hymenoptera, diptera and orthoptera (Gross, 1940; Blem, 1972; Caccamise, 1974; Brigham, 1990; Brigham and Fenton, 1991; Firman et al. 1993; Todd et al. 1998). Analyses of stomach contents have shown that flying ants and coleoptera represent 25% (i.e. 200 to 1800 ants/stomach) and 20% of the total food eaten, respectively (n = 87 individuals, Gross, 1940).


Interspecific Interactions

The Common Nighthawk is aggressive toward other similar species, such as the Antillean Nighthawk and the Chuck-will’s-widow (Bjorklund and Bjorklund, 1983). However, it is subordinate to bats at some feeding sites (Shields and Bildstein, 1979). The Lesser Nighthawk excludes the Common Nighthawk from its territory in certain desert regions of the southern United States where insect densities are low (Caccamise, 1974).

Potential predators of adult nighthawks include domestic cats (Felix catus), American Kestrels (Falco sparverius) and Peregrine Falcons (Falco peregrinus) (Poulin et al. 1996). Predation of eggs and nestlings by the American Crow (Corvus brachyrhynchos), Common Raven (Corvus corax), gulls, owls, coyotes (Canis latrans), striped skunks (Mephitis mephitis), dogs, foxes and snakes is regularly reported (Marzilli, 1989; Wedgwood, 1991).


Home Range and Territory

The Common Nighthawk is highly territorial and males seldom cross territorial boundaries (Wedgwood, 1973). Average territory size varies according to habitat and is estimated at approximately 10 ha in urban areas (Rust, 1947; Armstrong, 1965; Wedgwood, 1973) and 28.3 ha in natural areas (Wedgwood, 1973). Territory size can also vary according to the availability of suitable nest sites, as demonstrated by a study carried out in Florida, where the average distance between 16 nests was only 73 m (Sutherland, 1963). In Saskatchewan, the density of Common Nighthawk territories is higher in urban areas (1 male/18.6 ha) than in suburban areas (1 male/36.6 ha, n = 48, Wedgwood, 1973).


Behaviour and Adaptability

Since the middle of the 19th century, the Common Nighthawk has adapted well to urban areas in which buildings with flat gravel roofs provide suitable nest sites (Poulin et al. 1996). The species has also benefited from the abundance of insects around city lights and artificial habitats, such as treatment ponds.