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BC Conservation Data Centre: Conservation Status Report

Chordeiles minor
Common Nighthawk

 
Scientific Name: Chordeiles minor
English Name: Common Nighthawk
   
Provincial Status Summary
Status: S3S5B
Date Status Assigned: March 25, 2022
Date Last Reviewed: March 25, 2022
Reasons: This species is found over a wide area of the province of BC. There are however numerous threats across the breeding range in the province and in wintering areas. This species is appears to be undergoing significant declines throughout much its range.
 
Range
Range Extent: G = 200,000-2,500,000 square km
Range Extent Estimate (km2): 748,134
Range Extent Comments: Common Nighthawks in British Columbia are known from throughout the province, with the exception of west of the Coast Mountains north of Vancouver (where they are very rare) and the Queen Charlotte Islands (where they are accidental) (Campbell et al. 1990;Campbell et al. 2006; Brigham et al. 2011). They have been found from sea level to elevations of 1397m, with mean abundances greatest from 500-750 m (Boyd 2015) The range in BC appears stable with the distribution during the Breeding Bird Atlas equivalent to that described by Campbell et al. (1990).

Based on Breeding Bird Atlas, Breeding Bird Survey, and citizen science data, the range extent is estimated at approximately 748,000 square kilometres.
Area of Occupancy (km2): G = 501-2,500
Area of Occupancy Estimate (km2): 1729
Area of Occupancy Comments: Exact Common Nighthawk area of occupancy in British Columbia is unknown. The area of occupancy here was calculated based on occurrence data from Breeding Bird Atlas, Breeding Bird Survey, and citizen science data (eBird and BC Nightjar survey observations) to be 1,729 4-square kilometre cells. COSEWIC used an average territory size of 0.27 square kilometers for their estimates of the area of occupancy within all of Canada (approximately 54 000 square kilometers) (COSEWIC 2007). Other estimated territory sizes for Common Nighthawks range from 10.4 hectares to 28.3 ha (Brigham et al. 2011). Territorial system is dynamic (Brigham et al. 2011).
 
Occurrences & Population
Number of Occurrences: E = > 300
Comments: Common Nighthawk occurrences have not yet been mapped by the BC Conservation Data Centre. However, they are known to breed throughout most of British Columbia (Campbell et al. 1990). They have been labelled uncommon to common summer visitants throughout most of British Columbia, with exceptions being west of the Coast Ranges north of Vancouver, where they are very rare, and on the Queen Charlotte Islands, where they are accidental (Campbell et al. 1990).

The BC Breeding Bird Atlas lists detections in 594 map squares: 59 confirmed, 152 probable, and 383 possible breeding occurrences (Boyd 2015).
Number of Occurrences with Good Viability / Ecological Integrity: U = Unknown
Comments: It is not known how many occurrences have good viability. The species is widespread throughout the province, though is apparently most abundant in the southern half, which is also where the greatest human population centres and growth are expected.
Number of Occurrences Appropriately Protected & Managed: E = >40
Comments: While Common Nighthawks may occur on Crown land and within Parks and Protected areas (such as Okanagan Falls Provincial Park, an area near which they have been studied [Brigham 1990]), the success of their populations has not been a management or protection priority.
Population Size: FG = 10,000 - 1,000,000 individuals
Comments: PIF (2020) estimates the British Columbia population size as 500,000 (95% CL 250 000 to 870 000). Note however that the Breeding Bird Survey is not the ideal method for inventorying Common Nighthawk populations (RIC 1998) and it was not specifically designed to produce estimates of absolute population sizes (Blancher et al. 2007); nevertheless it is the most common survey of breeding birds across North America and Common Nighthawks are detected on survey routes. Accepting the assumptions and biases inherent in using Breeding Bird Survey results to estimate absolute population (Thogmartin et al. 2006). Previously, the provincial population size of Common Nighthawks was estimated at 400,000 individuals (PIF 2013). Haché et al. (2014) estimated the BC population at 24,859-51,001 (median 36,494) individuals. The highest probability of observation of Common Nighthawk comes from the Southern Interior, Central Interior, and Southern Interior Mountains, ecoprovinces (Boyd 2015). Most detections are in the southern half of the province (Campbell et al. 1990; Boyd 2015). Modelling of Canadian Common Nighthawk abundances shows the highest density of individuals in Canada occur in British Columbia (COSEWIC 2018).
 
Threats (to population, occurrences, or area affected)
Degree of Threat: BD = High - low
Comments: Potential threats in the province, identified following the IUCN categorization, include: 1.1 Housing and urban areas; 2.1 Annual and Perennial non-timber crops; and 7.3 Other ecosystem modifications.

Reasons for Common Nighthawk population declines have not been definitely determined (COSEWIC 2007,2018; Environment Canada 2016) and have not been thoroughly examined in British Columbia. Habitat loss and alteration in forest, agricultural and urban areas including, but not limited to: reforestation of abandoned agricultural fields and harvested forests; fire suppression; and a decrease in availability of flat, gravel roofs have been suggested as threats resulting in the decline (Campbell et al. 1990; COSEWIC 2007). A change in roof-construction practices is oft-cited as having a negative impact on nighthawks (e.g., Campbell et al. 2006; COSEWIC 2007; Brigham et al. 2011), but there is little evidence that this is a factor in the province where only 4 of 302 provincial nests were found on gravel rooftops (Campbell et al. 1990), and no birds were found either nesting or roosting on such sites over three years of study in Okanagan Falls designed to examine the importance of gravel roofs habitat for Common Nighthawks (Brigham 1989).

Reduced grazing, increased cultivation and intensive agriculture are suggested to have resulted in a reduction of suitable Common Nighthawk habitat (Jones and Bock 2002; COSEWIC 2007). Furthermore, preliminary data suggests that the percentage of agriculture is a significant negative predictor of nighthawk abundance in southern BC at both local (800 m) and landscape (5 km) scales (Elly Knight pers. comm.). While there have not been any direct studies, the decline of the Common Nighthawk (as well as other insectivorous neotropical migrants) has been suggested to be partly related to a general decline in insect populations at the breeding ground, wintering ground, or both, as a result of large-scale insecticide use since the mid-1990s (COSEWIC 2007). Other possible factors listed by COSEWIC (2007) include increased predation in urban and farming areas, collisions with motor vehicles, and climate change. Domestic animals have been recorded depredating nighthawks (Campbell et al. 2006), furthering risk associated with urban areas. The threats to British Columbian Common Nighthawk populations need to be studied in more detail to be definitively identified, and for their relative impacts to be assessed.
 
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: FH = Decline of <30% to increase of 25%
Comments: Across Canada, the most widely used measure of avian population trends is the Breeding Bird Survey. Although its methodology is not ideal for surveying Common Nighthawks (RIC 1998), the species is nevertheless recorded by the survey and so population trend information has been gathered. In British Columbia over the last ten years assessed (2009-2019), the mean annual percent change in bird population was a 0.52% survey-decline (with a confidence interval from -4.4% to 3.4%) (Smith et al. 2020). This indicates a population change of -5.09% (95% CL -35.9 to 39.7) over the 10 year period. Over time, the BC Nightjar Survey established in 2015 should provide more accurate trend data for the province, but that survey has relatively few years of data collection thus far and an analysis of trend from those surveys is not yet available. COSEWIC (2018) provides some estimate of declines in portions of the province, athough no estimates are available for the northernmost parts of BC.
Long-Term Trend: BE = Decline of 30-90%
Comments: BBS analysis 1970-2019 suggests an annual decline of -2.26% (95% CL -3.42 to -1.1) with ?medium reliability?. This indicates a population change of -67.4% (95%CL -81.8 to -41.8) over the 49 year period. In general, populations appear to be declining across North America (COSEWIC 2018), though may be increasing in localized areas (Brigham et al. 2011).
 
Other Factors
Intrinsic Vulnerability: BC=Moderately vulnerable to not intrinsically vulnerable.
Comments: There is very little information available regarding annual adult survival rates on either breeding or wintering grounds, on fledgling survival or reproductive success or productivity (COSEWIC 2007, 2018). Common Nighthawks are assumed to breed every year and are known to live at least 4 to 5 years, with up to 9 years old having been recovered from banding data (Brigham et al. 2011). Nestling Common Nighthawks are semi-precocial (Campbell et al. 1990; Brigham et al. 2011) and most nests in British Columbia contain two young (Fowle 1946; Brigham 1989; Campbell et al. 1990). Eggs are laid in mid-May and there is an 18 day incubation period on Vancouver Island, 19-20 days throughout the rest of British Columbia's records (Campbell et al. 1990). Usually only the female incubates (Campbell et al. 1990; Brigham et al. 2011). A study from the southern United States suggested that young Common Nighthawk nestlings are especially susceptible to overheating in high temperatures and would likely die without brooding, as they would not move to shade except by chance (Howell 1959); high temperatures on gravel roofs have been noted to cause nestling mortality in Common Nighthawk nests in eastern North America (COSEWIC 2007f), though likely not a threat in British Columbia owing to apparent low-levels of roof nesting, even historically. The first published Common Nighthawk reproductive rates were published from a Florida study (Perkins and Vickery 2007). Fourteen nests were found incidentally, eight of these failed (i.e. the whole brood [average clutch size = 1.93] was lost) (Perkins and Vickery 2007). They suggested that predation was the most common cause of nest failure (Perkins and Vickery 2007); the ground nesting habit of Common Nighthawks makes them especially vulnerable to predators (Brigham et al. 2011). Roadkill was the predominant mortality source reported in British Columbia (Campbell et al. 2006).
Environmental Specificity: C=Moderate. Generalist or community with some key requirements scarce.
Comments: In British Columbia, Campbell et al. (1990) found Common Nighthawks roosting and nesting in a variety of habitats including: beaches, farm fields, sagebrush and grassland habitat, open Ponderosa pine forests, rock outcrops, logged and slash-burned forest areas, coastal island meadows and urban areas. Ground substrates at nesting sites included gravel, sand, bare rock, wood chips, needles, leaves, and occasional living vegetation: lichen, dandelion and moss (Campbell et al. 1990). They lay on a horizontal surface, often more or less free of vegetation, such as in a field, clearing, rocky outcrop, or burnt forest (Armstrong 1965; Brigham et al. 2011); they were first reported nesting on flat, graveled roofs in 1869 (Armstrong 1965). Brigham (1989) suggested that published accounts indicating a high preference of Common Nighthawks for urban gravel rooftop nesting sites (e.g. Gramza 1967) may demonstrate an observer bias, rather than an ecological preference. In British Columbia, four nests have been recorded from rooftops, while 297 have been recorded from the ground (Campbell et al. 1990). So, while nighthawks may have benefited from new habitats provided by urban areas, they generally prefer natural roosting and nesting habitats (COSEWIC 2007). In a study of Common Nighthawks in Okanagan Falls, no bird was ever found nesting or roosting on flat roofs or any other man-made structure even though these habitats were available between the selected sites and foraging areas; they were found to nest on the ground and roost on the ground or in Ponderosa pine (Brigham 1989). Radio-tagged birds were found to change roost areas every 3.6 days on average (Brigham 1989). In Saskatchewan roosting males were found to prefer emerging trees in low canopy, low tree density stands on north-facing slopes (Fisher et al. 2004).
Other Rank Considerations: The decline in Common Nighthawk populations has been observed across Canada and the United States (COSEWIC 2018; Brigham et al. 2011). As the species is a long-distance migrant they are exposed to threats on the breeding, migratory, and wintering grounds. The impacts of wintering ground threats to the population are unknown, and it is not known with certainty where BC-breeding birds winter
 
Information Gaps
Research Needs: Caprimulgidae, the family to which the Common Nighthawk belongs, is one of the least studied in North America, in part because surveying can be particularly challenging (Brigham et al. 2011); relative to diurnal birds, and even owls, little is known about the basic biology and natural history of the Common Nighthawk (RIC 1998). Research priorities outlined in the recovery strategy (Environment Canada 2016) include: determining migratory connectivity, winter distribution, and non-breeding habitats; determine key demographic parameters; determine importance of known and suspected threats to species, its prey, and habitats; investigate factors affective productivity and survival; and evaluate the importance of aquatic systems for foraging and other characteristics of preferred sites. Breeding birds must be thoroughly surveyed to determine the characteristics of natural breeding sites and to determine the reproductive success relative to the nest site and foraging habitat in British Columbia. Determination of factors affecting low reproductive output, the type and amount of nest predation, and the longevity of breeders also needs to be studied. Several topics must be examined beyond provincial scales to include global limiting factors and trends in our understanding of Common Nighthawk population declines. Impacts of pesticide use on the prey base and relative fitness of breeding and overwintering Common Nighthawks is an important topic which may also be useful in the conservation of other insectivorous neotropical migrants.
Inventory Needs: In British Columbia there are few studies which assess the abundance of Common Nighthawks beyond the estimates provided by the Breeding Bird Survey (COSEWIC 2007). The WildResearch Nightjar survey is a citizen-science based initiative addressing this deficiency, and these surveys should be continued throughout British Columbia to increase knowledge of provincial trends (Knight 2017). This monitoring program was transfered to Birds Canada in 2020 (Coughlan 2020). Like the Breeding Bird Survey more routes in the northern part of the province are needed.
 
Stewardship
Protection: Common Nighthawks should be recorded and monitored where they occur in already existing protected areas. There are presently no programs in place for the protection of Common Nighthawk habitat (COSEWIC 2007); as data becomes available high quality nesting habitat should be identified for conservation.
Management: Common Nighthawks have been recorded using a wide variety of breeding habitat, including short-grass prairie, rocky outcrops, sand dunes, beaches, forest clearings, marshes, open forests, river banks, recently burned-over areas, recently logged areas, pastures, gravel roads, urban parks, mines, and commercial blueberry fields (COSEWIC 2007). Fire suppression and intensive agricultural use are thought to decrease suitable habitat. Campbell et al. (1990) suggested that regeneration of adjacent forest in the areas surrounding Greater Vancouver may account for the decline in Common Nighthawk numbers there. Further research into habitat preference and quality should be undertaken before initiating widespread habitat management treatments. Replacement of flat gravel roof tops with rubber has been implicated in nesting failure elsewhere, mitigation measures are discussed in Brigham et al. (2020).
 
Version
Author: N. Hentze updated by D.F.Fraser
Date: January 15, 2022
 
References
Armstrong, J.T. 1965. Breeding home range in the nighthawk and other birds: Its evolutionary and ecological significance. Ecology 46(5): 619-629.
Ashuelot Valley Environmental Observatory (AVEO). 2009. Project Nighthawk: Keene, NH project summary 2008. Available online at http://keeneweb.org/aveo/files/2009/01/project_nighthawk_report_2008.pdf
Bird Studies Canada. 2016. Wind Energy Bird and Bat Monitoring Database - Summary of the Findings from Post-construction Monitoring Reports. July 2016. http://www.bsc-eoc.org/resources/wind/Jul2016_Wind_database_summary.pdf
Bishop, C.A., and J.M. Brogan. 2013. Estimates of avian mortality attributed to vehicle collisions in Canada. Avian Conservation and Ecology 8:2. http://dx.doi.org/10.5751/ACE-00604-080202
Blancher, P.J. et al. 2007. Guide to the Partners in Flight Population Estimates Database. Version: North American Landbird Conservation Plan 2004. Partners in Flight Technical Series No 5.
Boyd, M. 2015. Common Nighthawk in Davidson, P.J.A., R.J. Cannings, A.R. Couturier, D. Lepage, and C.M. DiCorrado (eds.). The Atlas of Breeding Birds of British Columbia, 2008-2012. Bird Studies Canada, Delta, BC. http://www.birdatlas.bc.ca/accounts/speciesaccount.jsp?sp=CONI&lang=en
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Suggested Citation:

B.C. Conservation Data Centre. 2022. Conservation Status Report: Chordeiles minor. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Apr 16, 2024).