Nighthawk

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Nighthawk
Common nighthawk, Chordeiles minor
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Clade:	Strisores
Order:	Caprimulgiformes
Family:	Caprimulgidae
Subfamily:	Chordeilinae
Genera
Nyctiprogne Lurocalis Chordeiles

Nighthawks are nocturnal birds of the subfamily Chordeilinae, within the nightjar family, Caprimulgidae, which is a grouping of 92 species of medium sized birds with long wings and short bills specialized for eating insects.^[1] The nighthawk's subfamily consists of four genera: Chordeiles; Swainson, 1832, Lurocalis; Cassin, 1851, Podager; Wagler, 1832, and Nyctiprogne; Bonaparte, 1857, which are all native to the western hemisphere.^[2]

Species in the family Caprimulgidae exhibit similarities in plumage appearance, a fact that some attribute to convergent evolution, which occurs when species that do not share an evolutionary history develop similar adaptations, while others attribute it to parallelism which is the process by which similar adaptations arise in members of closely related species or populations.^[3] Because of this, taxonomists in the past experienced difficulty in categorizing members of this group, however new advancements in molecular phylogeny have allowed for more conclusive classification.^[3] Thanks to these techniques, it is now understood that there are nine genera in the family, not 16 as previously accepted, and that there are two main subfamilies: Caprimulginae (nightjars) and Chordeilinae which is the subfamily that nighthawks belong to.^[3] Because of this taxonomic complexity, a lot of information regarding nightjars is conflated with information regarding nighthawks. Nighthawks are similar in most respects to the nightjars, but have shorter bills and plumage that is less soft. Nighthawks are less strictly nocturnal than many nightjars and may be seen hunting when there is still light in the sky.^[3]

The subfamily Chordeilinae contains four genera and ten species.^[4] Under the genus Chordeiles exists the greatest number of diversity in species in the subfamily with the lesser nighthawk (Chordeiles acutipennis), the Antillean nighthawk (Chordeiles gundlachii), the common nighthawk (Chordeiles minor), the nacunda nighthawk (Chordeiles nacunda), the least nighthawk (Chordeiles pusillus), and the sand-colored nighthawk (Chordeiles rupestris) comprising the category.^[4] The genus Lurocalis contains the chestnut-banded nighthawk (Lurocalis nattereri), the Rufous-bellied nighthawk (Lurocalis rufiventris), and the short-tailed nighthawk (Lurocalis semitorquatus).^[4] There is only one species in the monotypic genus Nyctiprogne  which is the band-tailed nighthawk (Nyctiprogne leucopyga), a small bird differentiated from other nighthawks by it's long tail and dark appearance.^[4][5]

Image	Genus	Living species
	Nyctiprogne Bonaparte, 1857	Band-tailed nighthawk, Nyctiprogne leucopyga Plain-tailed nighthawk, Nyctiprogne vielliardi
	Lurocalis Cassin, 1851	Rufous-bellied nighthawk Lurocalis rufiventris Short-tailed nighthawk, Lurocalis semitorquatus Chestnut-banded nighthawk, Lurocalis nattereri
	Chordeiles Swainson, 1832	Nacunda nighthawk, Chordeiles nacunda Antillean nighthawk, Chordeiles gundlachii Lesser nighthawk, Chordeiles acutipennis Common nighthawk, Chordeiles minor Least nighthawk, Chordeiles pusillus Sand-colored nighthawk, Chordeiles rupestris

While limited information is known regarding the discovery of nighthawks, it is believed that the term "nighthawk", first recorded in the King James Bible of 1611, was originally a local name in England for the European nightjar.^[6] Its use in the Americas to refer to members of the genus Chordeiles and related genera was first recorded in 1778 when John Cassin, a renowned ornithologist responsible for the establishment of the Delaware County Institute of Science, established the classification.^[6][7] Fossil records indicate that specimens later identified to be the common nighthawks (Chordeiles minor) excavated in the Southwestern US could be traced back as far as 400,000 years (during the Pleistocene era) meaning that the subfamily has been an entrenched component of new world ecology for a significant duration of time.^[8]

Nighthawks are medium-sized birds averaging 9 inches (22–24 cm) from bill to tail with a wingspan of about 21-22 inches (53–57 cm), short legs, and very short, wide bills that are moderately hooked at the tip.^[9] The least nighthawk (Chordeiles pusillus), at 6.3 inches (15–19 cm) and 23 grams (0.81 oz), is the smallest of all Caprimulgiformes, while the Nacunda nighthawk (Chordeiles nacunda) is one of the largest nightjars in the world measuring at 11-13 inches (28–33 cm).^[10][11] Nighthawks have small feet, of little use for walking, and long pointed wings. Their soft plumage is cryptically coloured to resemble bark or leaves, aiding in protection from their primary predators; foxes and racoons.^[12] To promote concealment during the day, some species perch facing lengthwise along a branch, rather than across it as birds usually do.

• 
  Nighthawk wing markings
• 
  A nighthawk resting on a branch

Nighthawks are generally solitary but form flocks for the purpose of migration and for elaborate mating displays.^[13] These displays begin with the males diving from high in the air to produce the booming noises also associated with defense.^[14] This process is followed by tail-shaking, the exposing of a white patch located on the throat of the male, and vocalizations similar to croaks.^[14] Although it is unclear whether nighthawks mate for life, they are monogamous for the duration of mating season in which they develop a barren nest on the ground or another flat surface, such as an urban roof, where the female lays two patterned eggs directly onto bare ground.^[15] These eggs incubate for 18 to 20 days between May and August and they emerge semi-precocial, meaning they have their eyes open and a layer of down.^[14] Males will defend the nesting area, demonstrating indiscriminate aggression with displays involving diving and the production of a booming noise using their wings which deters predators and others of the same species.^[15] This unselective hostility can result in a decline in the average proportion of breeding individuals in a population in densely occupied territories, even below that of the carrying capacity established by available resources.^[15] This means that prey availability is not commonly cited as a concern for the conservation of nighthawks, but rather that habitat loss can be damaging to population stability.^[15] Nighthawks are mostly active in the late evening and early morning or at night and feed on moths and other large flying insects by holding their beak open in flight.^[16] There exists a mistaken belief that members of the Caprimulgidae family suck milk from goats (the Latin for goatsucker is Caprimulgus), however this claim is as of yet unsubstantiated.^[16] Heard most often at dusk, nighthawks have been known to perform a loud, nasal call which has been described as sounding like the noise "pee-yah".^[17]

Nighthawks are visually reliant predators that feed on flying insects such as beetles (Coleoptera), sawflies, bees, ants, and wasps (Hymenoptera), flies (Diptera), caddisflies (Trichoptera), butterflies, and moths (Lepidoptera) by opening their wide mouths to allow for the entrance of the insects as they are traveling.^[16] Areas of high precipitation, cool temperature, or high elevation are therefore unfavorable to nighthawks because flying insects are less mobile in such conditions.^[16] Nighthawks are most often observed hunting during crepuscular periods, or during twilight, which necessitates good eyesight with insects shorter than 5mm eliciting no reaction from experimental nighthawks.^[16] This consideration could pose a long-term risk to nighthawk population stability as climate change is increasing vulnerability in larger insects due to extreme weather events and higher temperatures, thus restricting prey availability for nighthawks which cannot see the, in some circumstances, 20% smaller prey organisms.^[18]

During the day, nighthawks roost in forested areas which provide them with cover from both predators and temperature fluctuations, although they may also occasionally be observed in grasslands and early successional habitats rich in foraging opportunities.^[19] Nighthawks breed in more open habitats like beaches or clearings to allow for the males to perform their mating rituals.^[14]

In October 2018, the University of Alberta published research on the common nighthawk revealing that it travels 20,000 km (12,000 mi) every year during migration between the rainforests and savannas of Brazil and its breeding grounds in northern Alberta.^[20] Further research has determined that, in addition to this annual migration between general regions, nighthawks demonstrate a high breeding site fidelity, thus meaning they are especially susceptible to destabilization as a result of natural disasters such as forest fires, floods or droughts, as well as anthropogenic interventions such as development.^[19] Nighthawks have been observed migrating at all hours of the day in flocks of, at times, hundreds of birds which winter in both rural and urban regions of South America.^[13] Nighthawk migration is considered one of the longest routes traveled for any North American bird.^[13]