Natural nesting habitat for Common Nighthawks (Chordeiles minor ) in the Northern Prairie region of North America is in decline due to row-crop conversion. Other nesting habitats used by nighthawks in this region includes flat, gravel rooftops, but such rooftop habitat is scheduled to be replaced by other materials within the next 20 years. These changes present substantial challenges to population persistence for nighthawks in this region.
This study used point counts and land cover analysis at 396 points in two study areas in southeastern South Dakota, northeastern Nebraska and northwestern Iowa to document that nighthawk presence is positively associated with flat, gravel rooftops and heterogeneous land cover and negatively associated with row crops in agriculturally dominated landscapes.
In addition to land cover change challenges, continuing trends toward increasing summer temperatures, decreasing cloud cover and increasing humidity might make rooftops unsuitable for nest habitat. Mean daily minimum, average and maximum operative temperatures (Te) recorded at rooftop nest sites in 2016-2017 were 26.3, 31.7, and 36.3 °C, respectively, with a 71.1 °C overall maximum Te. I monitored 50 rooftop nests during 2015-2017 in southeastern South Dakota. Like many nightjars, 7- to 14-day old nighthawk chicks are extremely heat tolerant. Evaporative water loss rates rapidly increased at temperatures above 44.1 °C in humid conditions (i.e. up to 16 °C dew point), and chicks had similar evaporative water loss rates at 51°C (2.44 g H20 h-1) to adult nightjars. However, baseline corticosterone levels increased in chicks acutely exposed to high ambient temperatures, suggesting that these temperatures were stressful. In addition, low hatching (0.252) and fledging (0.262) success rates, similar to those for other declining nighthawk populations, and a negative association between ambient temperature and hatching success, suggest that future microclimate trends may make rooftops an unsuitable nesting habitat.
This study recommends conservation of grasslands and heterogeneous landscapes of row crops and grazed pastures to promote nighthawk occurrence in the region where row crops dominate. In addition, provision of urban ecoroofs, with gravel patches, as alternative nesting habitats in agriculturally dominated landscapes will also be important for maintaining populations of this declining aerial insectivore species.
|Advisor:||Swanson, David L.|
|Commitee:||Brigham, R. Mark, Dixon, Mark D., Jarchow, Meghann E., Renner, Kenneth J.|
|School:||University of South Dakota|
|School Location:||United States -- South Dakota|
|Source:||DAI-B 80/01(E), Dissertation Abstracts International|
|Subjects:||Ecology, Agriculture, Physiology|
|Keywords:||Common nighthawk, Corticosterone, Land use change, Nesting success, Thermoregulation, Urban|
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