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The Common Nighthawk nest first discovered at our Rock Ridge MAPS site is still active. This adult, probably a female, spent the morning of June 16th incubating eggs in the blistering sun and seemed to be catching up on some sleep as well. I called in Seabrooke to sweep by on a net check with her long lens for a photograph and it turned out very nicely as usual. The eggs have been incubated since at least June 2, which means that the chicks should hatch no later than June 21 if they haven’t already. We will be back for our third visit to the site around the middle of next week and will hopefully find two “nighjarlets” at the little rock outcropping. I will also be conducting two point count routes in rock barren habitat next week. Each route will be four kilometres long, which gives me a good opportunity to turn up some more of these fascinating birds.
Whip-poor-wills, waiting for the next full moon to approach, have been quiet of late but we did flush three individuals from Canoe Lake (1 bird) and Perth (2 birds) Rds on our pre-dawn drive to Rock Ridge on the 16th.
Although arguably the most studied nightjar in North America, the Common Nighthawk remains poorly known (Poulin et.al. 1996).
Common Nighthawk (Chordeiles minor)
Habitat=primarily nests in open habitats such as rock barrens (also gravel roofs in urban areas)
Average clutch size=2
Nest building period=0 (no nest built)
Incubation period=19 days
Microhabitat=on ground on substrates of either rock, sand, gravel, lichens etc.
Egg colour=variable; creamy white to pale olive gray, heavily speckled with greys, browns and blacks.
Nest site selection=female
Parasitized by cowbirds=no
This Common Nighthawk nest was first discovered at our Rock Ridge MAPS site on June 2, 2009. The female was inadvertently flushed from the nest when traversing one of the countless rocky flats at the site. Incidentally, a Whip-poor-will nest was also discovered on this day, less than 1km from the nighthawk nest. There won’t be many days of nest searching where that happens! Both of these species of the nightjar family have been much in the news of late because of their concurrent and precipitous decline in populations. Common Nighthawk was officially designated as a Species at Risk by COSEWIC in 2007 (Threatened) while Whip-poor-will was just recently recommended for listing in April of this year (Threatened). Nightjars are most active at dawn and dusk and are uniquely adapted to a food source of flying insects such as moths. It is suggested that the presence of a tapeta lucidum, a reflective structure of the choroid part of the eye, aids their vision during low light levels (Nicol and Arnott 1974). Relatively little is known about the breeding ecology and population dynamics of these two species, both of which commonly breed in the Frontenac Arch region of Ontario. Project Whip-poor-will will be starting up soon and will be designed to survey all nightjar populations in the FBS study area.
The photo of the “nest” above is typical for Common Nighthawks where the eggs, usually two in a full clutch, are laid directly on the ground without any addition of materials or linings. They will sometime excavate a small scrape to contain the clutch but this activity seems to be determined by the habitat in which they choose to nest. The habitat for nesting nighthawks is quite variable, ranging from gravel rooftops in urban locations to a variety of open habitats adjacent to forests. They frequently inhabit rock barrens as in this particular case but will also nest in recently burned or clearcut forests as well as agricultural fields and grasslands throughout the continent.
This short video clip was recorded of a defensive adult just after it was flushed off the nest. The Birds of North American account for the species describes defensive behaviour by both sexes as follows:
Male does not directly guard the nest (Dexter 1952) but may dive and boom over nest sites (Rust 1947); in addition, male may defend nest by wing-beating and hissing with mouth wide open (Dexter 1952). Female may use injury-feigning behaviour (fly away, then hiss at intruder) when flushed from eggs or young (Tomkins 1942).
I spent no more than three minutes in the vicinity of the nest as I didn’t want to cause any excess amount of distress to the adult tending the eggs. I have a precise fix on its location and will be able to check on its progress at a distance from now on. The photos below provide a longer perspective on the nest site in terms of habitat. I have flushed several of both Common Nighthawk and Whip-poor-will in the area of our Rock Ridge MAPS station since the initial discovery of this nest but have not yet turned up any additional nest sites. The park has a large amount of suitable habitat for Common Nighthawks, perhaps about 1200 hectares worth, which suggests that the species might be common throughout rock barren areas. I will be traveling through much of the barrens starting next week for point count surveys and hope to encounter more of these fascinating birds.