Research666 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.

Summary 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. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12719/suppinfo is available for this article.

Common Nighthawk (Chordeiles minor) nesting habitat is limited to urban rooftops in southeastern South Dakota. Regional climate has changed from 1948 to 2016, with increases in humidity and solar radiation. Chicks exposed to high temperatures showed high baseline plasma corticosterone and low stress responses, suggesting that current climate influences stress response capacity.

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Heat tolerance for many birds under climate and land use change scenarios could be compromised in the future. Common Nighthawks (Chordeiles minor) belong to the Caprimulgiformes, a generally heat-tolerant order, but few studies have assessed heat tolerance in Caprimulgiform chicks, which might be particularly susceptible to heat stress. In the midwestern United States, nighthawks primarily nest on flat graveled rooftops in urban areas, as natural nesting habitats are limited. Urban rooftop-nesting nighthawks are likely exposed to higher environmental temperatures than birds nesting at more thermally buffered natural sites, and evaporative cooling might be impeded by the typically high summer humidity in their Midwest breeding range. This combination of heat and humidity might negatively impact heat tolerance of nighthawk chicks. We exposed 7- to 14-day-old nighthawk chicks (n = 15) from rooftop nests to ambient temperatures (Tas) up to 51°C and at typical summer dew points. Chicks initiated gular flutter at a mean ambient temperature of 42.4 ± 3.4°C (mean ± SE). Evaporative water loss (EWL) rates increased significantly with increasing temperature above 44.0 ± 1.5°C. Chicks showed little evidence of lower and upper bounds of the thermal neutral zone over the range of temperatures (30–44°C) for which we measured oxygen consumption. Body mass loss was significantly positively correlated with temperature during heat exposure trials. Chicks tolerated Tas up to 51°C and body temperatures (Tbs) up to 48°C, which, along with the high temperatures at which gular flutter and high rates of EWL were initiated, suggest that nighthawk chicks are tolerant of high ambient temperatures, even with relatively high humidity. Given the high rates of mass loss and high Tbs at hot ambient temperatures, chick heat tolerance mechanisms could be detrimental for rooftop-nesting nighthawks given projected increasing trends for both heat and humidity in the midwestern United States.