Common Nighthawk (Chordeiles minor) Habitat Associations and Activity Patterns in the Northern Boreal Forest

Abstract

Understanding how organisms interact with their environment is key to developing effective management strategies. Due to population declines detected in the southern part of their range, Common Nighthawks (Chordeiles minor) are listed as Threatened in Canada. Despite the northern boreal forest representing a significant portion of their breeding distribution, populations in these areas remain virtually un-studied and thus their numbers and biology are poorly understood. My study is one of the first to examine both temporal and spatial aspects of habitat associations for breeding nighthawks in the northern boreal forest. In the boreal region, fires create open habitats in an otherwise densely forested landscape. Considering nighthawks typically prefer open habitat, I assessed nighthawk abundance relative to forest age and vegetation characteristics to better understand spatial habitat associations in the northern boreal forest. I conducted evening roadside surveys and vegetation assessments along 20 different survey routes in 2015 and 2016, in the Yukon Territory, Canada. Nighthawks (both breeding and non-breeding individuals) were positively associated with open habitat at both the landscape and, within that, at the territory scale. At the landscape scale, I detected more individuals in early successional, post fire habitat compared to older, more densely vegetated forests. At the territory scale, nighthawks were negatively associated with denser tree canopy cover and greater cover by low shrubs. As well, I detected more birds on nights with colder temperatures and on nights with higher values of moon illumination. Given the association of this species with open habitats, land managers should be aware that the availability of early successional, post fire habitats may play a key role in the maintenance of populations of Common Nighthawks across the boreal region. Northern latitudes are characterized by a large variation in summer photoperiod, which has the potential to impact the activity patterns of these crepuscular birds. Because of this, the current Canadian National Nightjar Survey Protocol, which targets populations at southern latitudes, may be ineffective to accurately monitor northern populations. My goal was to assess nighthawk activity at northern latitudes and to provide recommendations for a targeted monitoring protocol, in the event that the current protocol was not suitable to accurately monitor these populations. I deployed autonomous recording units to record calling activity throughout the summers of 2015 and 2016, in the Yukon Territory, Canada, to better understand how temporal changes in ambient light and temperature impacts nighthawk activity. Daily activity period approximately reflected the length of civil twilight (sun 0-6 degrees below the horizon) and was constrained by nautical twilight (sun 7-12 degrees below the horizon) as nights grew darker. Calling activity was higher over the evening civil twilight period than the morning period. During the evening twilight window which my study targeted, nighthawks were more likely to call at low temperatures during low-light conditions and at higher temperatures during brighter conditions. Seasonally, calling activity increased during the first week of June and remained elevated until the first week of July. My data suggest that the recommended sampling times outlined in the Canadian National Nightjar Survey Protocol align with peak activity periods of nighthawks in our study area and that therefore this protocol should be used for future monitoring of northern nighthawk populations.