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Birds maintain some of the highest body temperatures among endothermic animals. Often deemed a selective advantage for heat tolerance, high body temperatures also limits birds' thermal safety margin before reaching lethal levels. Recent modelling suggests that sustained effort in Arctic birds might be restricted at mild air temperatures, which may require reductions in activity to avoid overheating, with expected negative impacts on reproductive performance. We measured within-individual changes in body temperature in calm birds and then in response to an experimental increase in activity in an outdoor captive population of Arctic, cold-specialised snow buntings (Plectrophenax nivalis), exposed to naturally varying air temperatures (− 15 to 36 °C). Calm buntings exhibited a modal body temperature range from 39.9 to 42.6 °C. However, we detected a significant increase in body temperature within minutes of shifting calm birds to active flight, with strong evidence for a positive effect of air temperature on body temperature (slope = 0.04 °C/ °C). Importantly, by an ambient temperature of 9 °C, flying buntings were already generating body temperatures ≥ 45 °C, approaching the upper thermal limits of organismal performance (45–47 °C). With known limited evaporative heat dissipation capacities in these birds, our results support the recent prediction that free-living buntings operating at maximal sustainable rates will increasingly need to rely on behavioural thermoregulatory strategies to regulate body temperature, to the detriment of nestling growth and survival. [ABSTRACT FROM AUTHOR]

Among birds, several body composition traits typically decrease in size or mass during breeding likely as a result of competing demands during this critical life history stage. However, a recent outdoor captive study in an Arctic-breeding cold-specialist songbird (snow buntings - Plectrophenax nivalis) demonstrated that these birds maintain winter cold acclimatization during the spring and summer, despite facing summer temperatures much warmer than on their Arctic breeding grounds. This suggests that buntings may face a cumulative physiological cost during breeding: having to support a winter phenotype while also upregulating additional traits for reproduction. The current study aimed to test this hypothesis. Between 2016 and 2019, we examined how body composition and metabolic performance (thermogenic capacity and physiological maintenance costs) changed from prebreeding to chick provisioning in free-living birds captured at the northern limit of their breeding range in the Canadian Arctic (Alert, NU, 82°). While body mass and fat reserves deceased significantly between pre-breeding and territory defense independent of thermal conditions, cold endurance and associated traits remained stable and elevated up to the nestling provisioning period, as long as ambient temperature remained below a threshold level of 0-2°C. These results indicate that snow buntings must maintain a high thermogenic capacity after arrival on the breeding grounds if temperatures remain below freezing, regardless of whether birds are actively breeding or not. In this context, our research suggests that these birds, and possibly other arctic breeding songbirds, may experience cumulative physiological costs during years with a late onset of spring, when breeding activities (i.e., egg production and incubation) begin while temperatures are still below 0-2°C. [ABSTRACT FROM AUTHOR]

There is increasing concern about the effect of underwater noise on fish due to rising levels of anthropogenic noise. We performed experiments on the black bullhead (Ameiurus melas), a species with known hearing specializations and located within the Laurentian Great Lakes where there is considerable commercial and recreational boat traffic. We tested and compared physiology (baseline cortisol), behaviour (activity, sheltering), and morphology (ciliary bundles of hair cells) of bullhead to boat noise. At 140 dB re 1 [micro]Pa (-54.84 dB re 1 mx[s.sup.-2]), we saw clear behavioural effects in terms of both activity and sheltering levels despite no obvious morphological or physiological stress. Following both short- and long-period acute exposure to higher--but environmentally relevant--noise levels, bullhead were less active and sheltered more and also exhibited a decrease in ciliary bundles. These results suggest that there are sublethal effects of anthropogenic noise on fish behaviour and ciliary bundles, which may have direct implications on population health. Moreover, commonly used metrics such as stress hormones may not always offer the most relevant biomarker of the response to anthropogenic boat noise. L'effet du bruit sous l'eau sur les poissons suscite de plus en plus d'inquietudes en raison des niveaux croissants de bruit d'origine humaine. Nous avons realise des experiences sur la barbotte noire (Ameiurus melas), une espece montrant des specialisations auditives presente dans les Grands Lacs laurentiens, le lieu d'une importante circulation d'embarcations commerciales et recreatives. Nous avons verifie et compare la physiologie (concentration de base de cortisol), le comportement (activite, mise a l'abri) et la morphologie (touffes ciliaires de cellules ciliees) de barbottes noires en presence de bruit d'embarcation. A 140 dB re 1 [micro]Pa (-54,84 dB re 1 mx[s.sup.-2]), nous avons note des effets comportementaux clairs en ce qui concerne les niveaux d'activite et de mise a l'abri, malgre l'absence de stress morphologique ou physiologique evident. Apres des periodes d'exposition aigue courtes et longues a des niveaux de bruit plus eleves, mais toujours pertinents sur le plan environnemental, les barbottes noires etaient moins actives et s'abritaient plus, en plus de presenter une diminution des touffes ciliaires. Ces resultats donnent a penser que le bruit d'origine humaine a des effets subletaux sur le comportement des poissons et les touffes ciliaires, qui pourraient avoir des consequences directes sur la sante des populations. En outre, des parametres couramment utilises comme la concentration d'hormones de stress pourraient ne pas toujours etre les biomarqueurs les plus pertinents de la reaction au bruit d'embarcations. [Traduit par la Redaction], Introduction Anthropogenic noise is now common in aquatic ecosystems, although the effects this has on aquatic animals, particularly freshwater fishes, remains unclear (Slabbekoorn et al. 2010; Popper and Hawkins 2012). [...]

Interspecific foraging associations (IFAs) are biological interactions where two or more species forage in association with each other. Climate‐induced reductions in Arctic sea ice have increased polar bear (Ursus maritimus) foraging in seabird colonies, which creates foraging opportunities for avian predators. We used drone video of bears foraging within a common eider (Somateria mollissima) colony on East Bay Island (Nunavut, Canada) in 2017 to investigate herring gull (Larus argentatus) foraging in association with bears. We recorded nest visitation by gulls following n = 193 eider flushing events from nests during incubation. The probability of gulls visiting eider nests increased with higher number of gulls present (β = 0.14 ± 0.03 [SE], p <.001) and for nests previously visited by a bear (β = 1.14 ± 0.49 [SE], p <.02). In our model examining the probability of gulls consuming eggs from nests, we failed to detect statistically significant effects for the number of gulls present (β = 0.09 ± 0.05 [SE], p <.07) or for nests previously visited by a bear (β = −0.92 ± 0.71 [SE], p <.19). Gulls preferred to visit nests behind bears (χ2 = 18, df = 1, p <.0001), indicating gulls are risk averse in the presence of polar bears. Our study provides novel insights on an Arctic IFA, and we present evidence that gulls capitalize on nests made available due to disturbance associated with foraging bears, as eiders disturbed off their nest allow gulls easier access to eggs. We suggest the IFA between gulls and polar bears is parasitic, as gulls are consuming terrestrial resources which would have eventually been consumed by bears. This finding has implications for estimating the energetic contribution of bird eggs to polar bear summer diets in that the total number of available clutches to consume may be reduced due to avian predators. [ABSTRACT FROM AUTHOR]

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The degree to which individuals adjust foraging behavior in response to environmental variability can impact foraging success, leading to downstream impacts on fitness and population dynamics. We examined the foraging flexibility, average daily energy expenditure, and foraging success of an ice‐associated Arctic seabird, the thick‐billed murre (Uria lomvia) in response to broad‐scale environmental conditions at two different‐sized, low Arctic colonies located <300 km apart. First, we compared foraging behavior (measured via GPS units), average daily energy expenditure (estimated from GPS derived activity budgets), and foraging success (nutritional state measured via nutritional biomarkers pre‐ and post‐ GPS deployment) of murres at two colonies, which differ greatly in size: 30,000 pairs breed on Coats Island, Nunavut, and 400,000 pairs breed on Digges Island, Nunavut. Second, we tested whether colony size within the same marine ecosystem altered foraging behavior in response to broad‐scale environmental variability. Third, we tested whether environmentally induced foraging flexibility influenced the foraging success of murres. Murres at the larger colony foraged farther and longer but made fewer trips, resulting in a lower nutritional state and lower foraging success compared to birds at the smaller colony. Foraging behavior and foraging success varied in response to environmental variation, with murres at both colonies making longer, more distant foraging trips in high ice regimes during incubation, suggesting flexibility in responding to environmental variability. However, only birds at the larger colony showed this same flexibility during chick rearing. Foraging success at both colonies was higher during high ice regimes, suggesting greater prey availability. Overall, murres from the larger colony exhibited lower foraging success, and their foraging behavior showed stronger responses to changes in broad‐scale conditions such as sea ice regime. Taken together, this suggests that larger Arctic seabird colonies have higher behavioral and demographic sensitivity to environmental change. [ABSTRACT FROM AUTHOR]