Habitat Use by Common Nighthawks (Chordeiles minor) in Canada's Boreal Forest
Foley, Gabriel Josiah
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Diurnal aerial insectivores, a guild of birds related by foraging behaviour, are declining rapidly across North America but the reasons for the decline are unknown. One of these guild members, the Common Nighthawk (Chordeiles minor), may have substantial but undocumented populations in Canada’s boreal forest. Any differences between Common Nighthawk population trends in the boreal forest compared to more southern populations may help determine why aerial insectivore populations in general are declining. Wildland fires, common in the boreal forest, transform closed habitat into the open habitat Common Nighthawks prefer. Therefore, I assessed nighthawk abundance in northwestern Ontario in recently burned forest (~5 years since a fire) compared to unburned boreal forest. Based on survey data, Common Nighthawks were significantly more abundant in burned boreal forest than unburned forest, and the probability of detecting birds decreased with distance from a burn. Nighthawks were not more associated with riverine areas than other areas in my study area. I also evaluated forest attributes that may affect local nighthawk abundance. Lesser canopy cover and the number of logs in recently burned forest are likely important factors in habitat use by Common Nighthawks, but these factors are dependent upon the scale used for the evaluation. Common Nighthawks, like other nightjars, often sit on gravel roads at night where they are at risk of being struck by passing traffic, but neither the reasons behind their use of roads nor the frequency of traffic strikes are known. I found no significant vegetation structure variable that predicted nighthawk site use on roads. Further, neither nearby Common Nighthawk abundance nor nearby potential roost availability predicted presence. However, the overall frequency of Common Nighthawks on roads was significantly correlated with lunar phase, which suggests that Common Nighthawks (subfamily Chordeilinae) use roads as a foraging site like other nightjars (subfamily Caprimulginae). The low vehicle-induced mortality I observed likely results from the low traffic rate at my study site, thus the use of gravel roads by Common Nighthawks in the boreal forest, assuming similar levels of traffic, does not appear to be a substantial conservation threat.