Habitat Associations, Nest Success and Nest Microclimate of Rooftop Nesting Common Nighthawks (Chordeiles minor) in the Agriculturally Dominant Landscape of Southeastern South Dakota

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

Data from: Success despite the stress: violet-green swallows increase glucocorticoids and maintain reproductive output despite experimental increases in flight costs

Glucocorticoid steroid hormones play a central role in regulating the metabolic state of animals, especially when they cope with unanticipated stressors in their environment. The cort-adaptation hypothesis predicts that baseline concentrations of glucocorticoids are adjusted upward to match energetic needs and promote fitness when individuals are faced with physiological challenges, including those associated with reproduction. We tested the cort-adaptation hypothesis in the violet-green swallow (Tachycineta thalassina) by experimentally increasing flight costs during the offspring rearing period. Individual females were assigned to one of three treatments: light feather clipping (removal of four wing feathers), heavy feather clipping (removal of eight wing feathers) or a sham-clip control. We measured baseline corticosterone and body mass immediately prior to implementing treatments during the offspring rearing period and then 10 days after initial manipulations took place. We also quantified risk-taking behaviour, offspring feeding rate and the number of offspring fledged. Finally, we examined how treatments influenced offspring phenotype via measurements of nestling body mass and baseline corticosterone, as both measures have been associated with post-fledging survival. We found that handicapped females significantly increased baseline corticosterone between the two sampling periods, with the magnitude of change in the light clipping and heavy clipping treatments 2·5× and 6·1× greater than controls, respectively. All individuals lost mass between the two sampling periods, but the degree of loss was greater for females in both clipping treatments relative to unmanipulated controls. In contrast, we found no evidence of treatment differences in female risk-taking, offspring provisioning or in the number of offspring fledged. Offspring raised by females in both handicapped treatments did have significantly elevated baseline corticosterone relative to those in control broods, but we detected no treatment differences in offspring body mass. Our study found that handicapped females increased circulating glucocorticoids and were able to maintain critical parental care behaviours and raise a similar number of offspring as unmanipulated controls. Thus, increases in baseline cort of handicapped females appeared to have allowed them to maintain fitness despite increased physiological challenges, providing support for the cort-adaptation hypothesis

RiversetalVGSWHandicappingRawData

This file contains data used to assess variation in pre-treatment measurements of adult females (tab1-tab2); data used to assess treatment effects on adult female baseline corticosterone, body mass, number of offspring fledged (tab3-tab4); data used to assess feeding rates by males, females, and males + females combined (tab5-tab7); data used to assess treatment effects on offspring body mass and baseline corticosterone (tab8); and data used to assess treatment effects on the time for females to enter nest boxes in the presence of a novel object (tab9)

Comprehensive estimation of spatial and temporal migratory connectivity across the annual cycle to direct conservation efforts

Migratory connectivity is the degree to which populations are linked in space and time across the annual cycle. Low connectivity indicates mixing of populations while high connectivity indicates population separation in space or time. High migratory connectivity makes individual populations susceptible to local environmental conditions; therefore, evaluating migratory connectivity continuously across a species range is important for understanding differential population trends and revealing places and times contributing to these differences. The common nighthawk Chordeiles minor is a widespread, declining, long‐distance migratory bird. Variable population trends across the nighthawk breeding range suggest that knowledge of migratory connectivity is needed to direct conservation. We used GPS tags to track 52 individuals from 12 breeding populations. We estimated migratory connectivity as 0.29 (Mantel coefficient: 0 = no connectivity, 1 = full connectivity) between the breeding and wintering grounds. We then estimated migratory connectivity at every latitude (spatial connectivity) or day (temporal connectivity) of migration and smoothed those migratory connectivity estimates to produce continuous migratory connectivity ‘profiles'. Spatial and temporal connectivity were highest during migration through North America (around 0.3–0.6), with values generally around 0 in Central and South America due to mixing of populations along a common migratory route and similar migration timing across populations. We found local peaks in spatial and temporal connectivity during migration associated with crossing the Gulf of Mexico. We used simulations to estimate the probability that our method missed peaks (spatial: 0.12, temporal: 0.18) or detected false peaks (spatial: 0.11, temporal: 0.37) due to data gaps and showed that our approach remains useful even for sparse and/or sporadic location data. Our study presents a generalizable approach to evaluating migratory connectivity across the full annual cycle that can be used to focus migratory bird conservation towards places and times of the annual cycle where populations are more likely to be limited