Background & Hypotheses
The common nighthawk (Chordeiles minor, or 'CONI') is an elusive species in many ways. Its name, "nighthawk", is wildly deceiving as it is not nocturnal or a hawk. Rather, the common nighthawk is a crepuscular nightjar species, meaning it is most active at dawn and dusk (Viel, 2014; Brigham et al., 2020). Despite being the most frequently studied and referenced nightjar throughout the Americas, relatively little is "commonly" known about its life history and behavior (Brigham et al., 2020). A lack of information on the common nighthawk is partly due to its cryptic, mottled brown plumage that blends in with its flat, open nest sites and makes it difficult to spot (COSEWIC, 2018; Brigham et al., 2020). Most often, nighthawks are identified in flight, while foraging for aerial insects at dusk, or by their characteristic vocalizations (Armstrong, 1965; Viel, 2014; Brigham et al., 2020; Hannah et al., 2022). During the breeding season, males dive from hundreds of meters in the sky, during which air rushes past their feathers to create a "booming" sound that serves as both a breeding and territorial display (Viel, 2014; Brigham et al., 2020).
The Common Nighthawk is listed as a species of Special Concern in Canada where its southern populations have declined by 68% in the past 50 years (COSEWIC, 2018) (Figure 1). These declines echo across North America, where breeding populations have observed a 2.1% annual decline (Viel, 2014; Brigham et al., 2020). Like much about this species, the cause of these declines has yet to be confirmed. Experts suggest a reduction in the nighthawk's habitat availability and insectivorous food supply, resulting from climate change and pesticide use, as a probable cause (Viel, 2014; COSEWIC, 2018; Brigham et al., 2020).
A growing body of research has revealed the ability of artificial light to significantly alter many species' physiology and behavior, including the onset of daily activity and feeding behavior (Sanders et al., 2020). It has been suggested that common nighthawks may utilize artificial light to attract insectivorous prey and extend their foraging period (Ingles et al., 1999; Brigham et al., 2020). Indeed, common nighthawks are more likely to be found in areas with artificial light (Armstrong, 1965; Viel, 2014) and have been incidentally observed foraging under sources of artificial light (Ingles et al., 1999; Foley & Wszola, 2017). What remains to be seen is if artificial light alters the intensity and timing of habitat use in areas where common nighthawk occupancy is confirmed. |
This project expects the intensity of habitat use by the common nighthawk to be observably higher in areas where artificial light is present (and insects more abundant), either due to denser populations or more frequent use by the same individuals, and that habitat use will extend beyond dusk in places where consistent artificial lighting permitted them to detect prey. Additionally, it is expected that territorial and breeding activity would be higher in habitats with artificial light, as nesting near a habitat with consistent food supplies would reduce the required energy expenditure for foraging.
A lack of substantial research into this topic can be attributed to the common nighthawk's low abundancies, inconspicuous appearance, and inopportune timing of activity, which render it difficult to detect (Viel et al., 2014; Knight et al., 2017). While considerable citizen science efforts to monitor Common Nighthawk populations have been conducted, these projects are resource intensive, limited to easily accessible areas, and prone to observer bias (Viel, 2014; Noble-Dalton & Knight, 2020). Luckily, the Common Nighthawk's simple, distinct, and frequent auditory signals make it a prime candidate for acoustic monitoring with autonomic recording units (ARUs) and automated signal recognition software (Knight et al., 2017). Though initially expensive to implement, ARUs and autonomic recognition offer many advantages for rare species monitoring, including greater spatial and temporal detail, increased efficiency and precision by providing repeated samples with less effort, reduced levels of observer bias, and a bank of permanent records of raw data for future analysis (Shonfield & Bayne, 2017).
Project Rationale & Objectives
As an example of the ongoing value of acoustic monitoring, this project utilizes an extensive set of existing acoustic data collected by the Bayne lab at the University of Alberta and the Alberta Biodiversity Monitoring Institute (ABMI) to assess common nighthawk activity in varying lighting conditions across Alberta’s boreal forest to address the following research questions:
Primary Research Question:
Do habitats illuminated by artificial light observe higher levels of common nighthawk activity than those without artificial light in Alberta's boreal forest?
Secondary Research Questions:
- Are higher levels of habitat use in areas illuminated by artificial light observed consistently or only during the foraging period?
- Does common nighthawk activity extended beyond dusk in illuminated habitats? Does it extend later than nighthawk activity observed in nonilluminated habitats?
- Are illuminated habitats only used for foraging (indicated by the presence of vocalizations) or are they also utilized as mating or nesting habitat (indicated by the presence of wing booms)?
Answering these questions can provide insight into the potential contributors to population declines. If illuminated habitats see higher levels of common nighthawk use, then the provision of artificial light may be utilized as a short-term recovery measure. If the alternative hypothesis that there is no observable effect of artificial light on nighthawk habitat use is true, then the provision of artificial light will not be a suitable intervention in population recovery. If lower levels of common nighthawk activity are observed in illuminated habitats, a second alternative hypothesis suggesting that artificial light may lead to an increased predation risk would need to be explored.
The Common Nighthawk is listed under Canada's Migratory Birds Act and Species at Risk Act, forming a legal mandate to protect this species and its habitat from disturbance or harm. Thus, the outcomes of this project are not only paramount to conserving the species but also serve to benefit private interests as levels of artificial lighting are more easily addressed than other potential causes of decline, such as commercial agricultural practices, land conversion, and climate change, particularly for the industrial sectors that occupy Alberta's boreal, where this project is located.