Common Nighthawk

Common Nighthawk
In British Columbia, Canada
Conservation status
Least Concern (IUCN 3.1),[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Caprimulgiformes
Family:	Caprimulgidae
Genus:	Chordeiles
Species:	C. minor
Binomial name
Chordeiles minor (J. R. Forster, 1771)[2]
Subspecies
See text.
Synonyms
Caprimulgus minor Chordeiles virginianus

The Common Nighthawk (Chordeiles minor) is a medium-sized ^[3][4] crepuscular or nocturnal bird,^[3][5] whose presence and identity are best revealed by its vocalization. Typically dark^[3] (grey, black and brown^[5]), displaying cryptic colouration and intricate patterns, this bird becomes invisible by day. Once aerial, with its buoyant but erratic flight, this bird is most conspicuous. The most remarkable feature of this aerial insectivore is its small beak belies the massiveness of its mouth. Some claim appearance similarities to owls. With its horizontal stance^[3] and short legs, the Common Nighthawk does not travel frequently on the ground, instead preferring to perch horizontally, parallel to branches, on posts, on the ground or on a roof.^[5] The males of this species may roost together but the bird is primarily solitary. The Common Nighthawk shows variability in territory size.^[4]

This caprimulguid has a large, flattened head with large eyes; facially it lacks rictal bristles. The Common Nighthawk has long slender wings that at rest extend beyond a notched tail. There is noticeable barring on the sides and abdomen,^[4] also white wing-patches.^[3]

The Common Nighthawk measures 22-25 cm in length,^[4] displays a wing span of 21-24” / 54–61 cm,^[6] weighs 62-98 g,^[4][6] and has a life span of 4–5 years.^[4]

Taxonomy

Within family Caprimulgidae, subfamily Chordeilinae (Nighthawks) are limited to the New World and are distinguished from the subfamily Caprimulginae, by the lack of rictal bristles.

The American Orinthologists’ Union treated the smaller Antillean Nighthawk as conspecific with the Common Nighthawk until 1982.^[4]

Up until the early 19th century, the Common Nighthawk and the Whip-poor-will were thought to be one species. The latter’s call was explained as the nocturnal expression of the Common Nighthawk. Alexander Wilson, “The Father of American Ornithology” correctly made the differentiation between the two species.

Subspecies

Chordeiles minor panamensis (Eisenmann, 1962)

• breeds on
  • Pacific slope of Panama and north west Costa Rica
  • noted to depart Panama during winter for points in South America

Chordeiles minor neotropicalis (Selander & Alvarez del Toro, 1955)

• breeds in
  • south Mexico
  • Honduras

Chordeiles minor howelli (Oberholser, 1914)

• breeds in
  • west central United States (north Texas, west Oklahoma, and Kansas to east Colorado, less typical form in central Colorado, north east Utah and Wyoming)
• darker than sennetti and paler and less cinnamon than henryi

Chordeiles minor hesperis (Grinnell, 1905)

• breeds in
  • south west Canada (British Columbia and Alberta)
  • western interior of United States (Washington, Montana, Nevada, interior California, Utah, extreme north Colorado, west Wyoming)
• darker than sennetti and paler and less cinnamon than henryi

Chordeiles minor aserriensis (Cherrie, 1896)

• breeds from
  • south central Texas to north Mexico
• darker than sennetti and paler and less cinnamon than henryi

Chordeiles minor chapmani (Coues, 1888)

• breeds from
  • South East Kansas to east North Carolina and southwards to south east Texas and south Florida
• darkest

Chordeiles minor sennetti (Coues, 1888)

• breeds in
  • north Great Plains: east Montana, south Saskatchewan
  • Manitoba, southwards to North Dakota, Minnesota and Iowa
• palest

Chordeiles minor henryi (Cassin, 1855)

• breeds from
  • south east Utah and south west Colorado through mountains of west Texas, Arizona and New Mexico (less north east) to east Sonora, Chihuahua, and Durango
• unique with ochraceous to deep cinnamon feather edges on upperparts

Chordeiles minor minor (J. R. Forster, 1771)

• breeds from
  • south east Alaska to Vancouver Island, British Columbia, Canada
  • south Canada/northern United States (Minnesota, Indiana) to Virginia, North Carolina, Georgia and Oklahoma
• darkest^[7]

History

This species is recorded as widespread during the Late Pleistocene, from Virginia to California and from Wyoming to Texas.^[4]

In the late 19th and early 20th century, because they held the title of "hawk" in their names, had habits of diurnal insect hunting, and the fact that they travelled in migrating flocks, worked against these birds in that they were hunted for sport, nourishment and as predators.^[6]

Field Identification

The Common Nighthawk is distinct from other caprimulguids with its showing of a forked tail (includes a white bar in females); long, unbarred, pointed wings with a distinguished white patch; the lack of rictal bristles, and the key identifier – their unmistakable calls.^[7]

The Common Nighthawk resembles both the Antillean Nighthawk and Lesser Nighthawk. The Lesser Nighthawk is a smaller bird and displays more buffy on the undertail coverts, where the Common Nighthawk shows white. Common Nighthawks and Antillean Nighthawks exhibit entirely dark on the basal portion of the primary feathers, whereas Lesser Nighthawks have bands of buffy spots. Common Nighthawks and Antillean Nighthawks have a longer, outermost primary conveying a pointier wing tip than the Lesser Nighthawk. The Common Nighthawk forages higher above ground than the Lesser Nighthawk and has a different call. The Antillean Nighthawk may only be distinguished as different from the Common Nighthawk, once in the hand. Subtle differences are recorded to be a challenge in field identification.^[4]

Habitat and Distribution

The Common Nighthawk may be found in forests, desert, savannahs, beach and desert scrub, cities,^[3] and prairies,^[4] at elevations of sea level or below to 12000 ft / 3600 m .^[3] They are one of a handful of birds that are known to inhabit recently burned forests, and then dwindle in numbers, as successional growth occurs over the succeeding years or decades. The Common Nighthawk is drawn into urban built-up areas by insects.^[5]

The Common Nighthawk is the only Nighthawk occurring over the majority of northern North America.

Food availability is likely a key factor in determining which and when areas are suitable for habitation. The Common Nighthawk is not well designed to survive in poor conditions, specifically low food availability. Therefore, a constant food supply consistent with warmer temperatures is a driving force for migration and ultimately survival.

It is thought that the bird is not able to enter torpor,^[4] although recent evidence suggests the opposite.^[7]

Migration

Journey length 2500–6800 miles / 4000–11000 km.

The Common Nighthawk will migrate by day or night in loose flocks; frequently numbering in the thousands,^[6] no visible leader has been observed. The enormous distance travelled between breeding grounds and wintering range displays one of the North America’s longer migrations. The north bound journey commences at the end of February and the birds reach destinations as late as mid June. The south bound migration commences mid July and reaches a close in early October.^[4]

While migrating, these birds have been reported travelling through middle America, Florida, the West Indies,^[6] Cuba, the Caribbean and Bermuda,^[4] finally completing their journey in the wintering grounds of South America,^[6][7] primarily Argentina.^[7]

As aerial insectivores, the migrants will feed on route,^[6] congregating to hunt in marshes, rivers and on lakeshores. In Manitoba and Ontario, Canada, it is reported that during migration the Nighthawks are seen most commonly in the late afternoon, into the evening,^[4][5] with a burst of sunset feeding activities.^[5]

Additionally, it has been noted that during migration the birds may fly closer to the ground than normal; possibly foraging for insects. There is speculation that feeding also occurs at higher altitudes.

The Common Nighthawk winters in the South Americas, but distribution in this locale is poorly known due to difficulties in distinguishing the bird from the Lesser Nighthawk and in differentiating between migrants and over wintering birds. In some South and Central American countries, a lack of study has led to restricted and incomplete records of the bird. Records do support wintering in Ecuador, Peru, Bolivia, Brazil, Paraguay, Uruguay and Argentina.^[4]

Moult

In the Common Nighthawk all bodily plumage and rectrices are replaced in the post-juvenile moult. Post-juvenile moult commences in September at the breeding grounds; majority of the body plumage is replaced but wing-coverts and rectrices are not completed until January–February, once the bird arrives at the wintering grounds. There is no other moult prior to the annual moult of the adult. The Common Nighthawk adults have a complete moult that occurs mostly or completely on wintering grounds and is not ceased until January or February.^[7]

Behavior

Vocalization

No differences between calls or song in the Common Nighthawk. The most conspicuous vocalization is a nasal peent or beernt during even flight. Peak vocalizations are reported 30–45 minutes after sunset.

Croaking auk auk auk vocalized by males while in the presence of a female during courtship. Another courtship sound, thought to be made solely by the males, is the boom, created by air rushing through the primaries after a quick down flex of the wings during a daytime dive.

Hissing cluck heard by females, and wing-clapping by male during nest defence. Strongly territorial males perform dives against fledglings, females and intruders such as humans or raccoons.^[4]

Feeding and Diet

Frequent flyers, the long-winged Common Nighthawk hunts on the wing^[7] for extended periods at high altitudes or in open areas.^[5] Crepuscular, flying insects are its preferred food source. Cessation of the hunt as dusk becomes night, resumes when night becomes dawn.^[7] Nighttime (darkness) feeding is rare,^[4] even on evenings with a full moon.^[7] The bird displays opportunistic feeding tendencies, although it may be able to fine-tune its meal choice in the moments before capture.

Vision presumed to be main detection sense. No evidence exists to support the use of echolocation. The birds have been observed to converge on artificial light sources in an effort to forage for insects enticed by the light.^[4] The average flight speed of Common Nighthawks is 23.4 kilometers per hour.^[8]

Drinking, Pellet-Casting and Droppings

The Common Nighthawk was observed to drink on its winter range by flying extremely low over the surface of the water.^[9]

No evidence suggests this bird casts pellets.

The Common Nighthawk is recognized to discharge feces around nest and roosting positions. The bird will sporadically defecate in flight. Defecation is pungent.^[4]

Reproduction and Nesting

The Common Nighthawk breeds during the period of mid March to early October.^[6] It most commonly has a first and only brood, however sometimes a second later brood. The bird is assumed to breed every year. Reuse of nests by females in subsequent years has been reported.^[4] A monogamous pattern has also recently been confirmed.^[7]

Courting and mate selection occurs partially in flight, the male dives and booms (see Vocalization) in an effort to garner female attention,^[4][5] the female may be in flight herself or stationary on the ground.

Copulation occurs when the pair settles on the ground together; the male with his rocking body, widespread tail wagging and bulging throat expresses guttural croaking sounds. This display by the male is performed repeatedly until copulation.^[4]

The preferred breeding / nesting habitat is in forested regions with expansive rocky outcrops, in clearings, in burned areas^[5] or in small patches of sandy gravel.^[4] The eggs are not laid in a nest, instead laid on bare rock, gravel^[5] or sometimes a living substrate such as lichen.^[4] Least popular are breeding sites in agricultural settings.^[10] As displayed in the latter portion of the 20th century, urban breeding is in decline.^[5] If urban breeding sites do occur; they are observed on flat, gravel rooftops.

It is a solitary nester putting great distances between other pairs of the same species, a nest would more commonly occur in closer proximity to other species of birds.

Females choose the nest site and are the primary incubators of the eggs (males will incubate occasionally), incubation time varies but is approximately 18 days. The female will leave the nest unattended during the evening in order to feed. The male will roost in a neighbouring tree (the spot he chooses changes daily); he guards the nest by diving, hissing, wing-beating or booming at the sites. In the face of predation, Common Nighthawks do not abandon the nest easily; instead likely rely on their cryptic colouration to camouflage themselves. If a departure does occur the females have been noted to fly away, hissing at the intruder^[4] or to perform a disturbance display.^[7]

Incubation, Hatching and Young

The eggs are elliptical shaped, strong, variably coloured with heavy speckling. The Common Nighthawk displays two, 6-7g, eggs per clutch; the eggs are laid over a period of 1–2 days. The female alone displays a brood patch.

The infants may be heard peeping in the hours before they hatch. Once the infants have broken out of the shells, there is a requirement to remove the debris in order to avoid predators. The mother may carry the eggshells to another location or consume a portion of them. Once hatched, the nestlings are active and have their eyes fully or half open, additionally they display a sparing cover of soft down feathers. The infants are semiprecocial. By day 2, the hatchling’s bodily mass will double and they will be able to self propel towards their mothers call. The young will hiss at an intruder.

The young are fed by regurgitation before sunrise and after sunset. The male parent will assist in feeding fledglings and will also feed the female during nesting. No records exist to support the parent’s ability to physically carry a chick.

On their 18th day, the young will make their first flight; by days 25-30, they are flying proficiently. The young are last seen with their parents on day 30. Complete development is shown between their 45-50th day. At day 52, the juvenile will join the flock, potentially migrating. Juvenile birds, in both sexes, are lighter in colour and have a smaller white wing-patch, than adult Common Nighthawks.^[4]

Status and Conservation

There has been a general decline in the number of Common Nighthawks in North America, but some population increases also have occurred ^[4] in other geographical locations.^[7] The bird’s large range makes individual risk thresholds in specific regions difficult to establish.^[1]

The Common Nighthawk’s trait of being a ground nesting bird makes it particularly susceptible to predators some of which include domestic cats, ravens, snakes, dogs, coyotes, falcons and owls.

Lack of flat roofs, pesticides,^[4] increased predation and loss of habitat^[7] are noted factors of their decline. Further, unstudied potential causes of decline include climate change, disease, road kills, man-made towers (as an aerial hazard) and parasites.^[4]

The absence of flat roofs (made with gravel) in urban settings is a important cause of decline. In an effort to provide managed breeding areas, gravel pads have been added in the corners of rubberized roofs; this proves acceptable, as nesting has been observed.^[7]

• 

  Painting by Robert W. Hines

• 

  Nighthawk in Flight, Miami FL

References

1. ^ ^{a b} IUCN Red List of Threatened Species. 2011. “Common Nighthawk”. Retrieved 5 Oct 2011, from http://www.iucnredlist.org/apps/redlist/details/143363/0
2. ^ "Chordeiles minor". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=177979. Retrieved 25 May 2010. 
3. ^ ^{a b c d e f g} The Sibley Guide to Bird Life & Behaviour. Chanticleer Press, Inc., 2001.
4. ^ ^{a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac} Poulin, R., Grindal, S., & Brigham, R. 1996. Common Nighthawk. No. 213. The Birds of North America. The American Ornithologists’ Union.
5. ^ ^{a b c d e f g h i j k} Manitoba Avian Research Committee, Manitoba Naturalists Society. The Birds of Manitoba. Friesens Printers, 2003.
6. ^ ^{a b c d e f g h} Elphick, J. Atlas of Bird Migration. Firefly Books, 2007.
7. ^ ^{a b c d e f g h i j k l m n} Holyoak, D. Nightjars and their Allies, The Caprimulgiformes. Oxford University Press, 2001.
8. ^ Brigham, R. M., M. B. Fenton and H. D. J N. Aldridge. 1998. Flight Speed of Foraging Common Nighthawks (Chordeiles minor): Does the Measurement Technique Matter? American Midland Naturalist 139(2):325-330
9. ^ Canevari, M., Canevari, P., Carrizo, G., Harris, G., Mata, J., & Straneck, R. 1991. Nueva guia de la saves Argentinas. 2 vols. Fundacion Acindar, Buenos Aires, cited in Poulin, R., Grindal, S., & Brigham, R. 1996. Common Nighthawk. No. 213. The Birds of North America. The American Ornithologists’ Union.
10. ^ Gillette, L. 1991. Survey of Common Nighthawks in Minnesota, 1990. The Loon, 62:141-143, cited in Manitoba Avian Research Committee, Manitoba Naturalists Society. The Birds of Manitoba. Friesens Printers, 2003, p.238.

External links

• All About Birds, The Cornell Lab of Orinthology
• Chordeiles minor (Common Nighthawk), IUCN Red List of Threatened Species