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Synopsis Temperate winters can impose severe conditions on songbirds that threaten survival, including shorter days and often lower temperatures and food availability. One well-studied mechanism by which songbirds cope with such conditions is seasonal acclimatization of thermal metabolic traits, with strong evidence for both preparative and responsive changes in thermogenic capacity (i.e., the ability to generate heat) to low winter temperatures. However, a bird’s ability to cope with seasonal extremes or unpredictable events is likely dependent on a combination of behavioral and physiological traits that function to maintain allostatic balance. The ability to cope with reduced food availability may be an important component of organismal response to temperate winters in songbirds. Here, we compare responses to experimentally reduced food availability at different times of year in captive red crossbills (Loxia curvirostra) and pine siskins (Spinus pinus)—two species that cope with variable food resources and live in cold places—to investigate seasonal changes in the organismal response to food availability. Further, red crossbills are known to use social information to improve responses to reduced food availability, so we also examine whether the use of social information in this context varies seasonally in this species. We find that pine siskins and red crossbills lose less body mass during time-restricted feedings in late winter compared to summer, and that red crossbills further benefit from social information gathered from observing other food-restricted red crossbills in both seasons. Observed changes in body mass were only partially explained by seasonal differences in food intake. Our results demonstrate seasonal acclimation to food stress and social information use across seasons in a controlled captive environment and highlight the importance of considering diverse physiological systems (e.g., thermogenic, metabolic, digestive, etc.) to understand organismal responses to environmental challenges.
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A challenge of warmer temperate winters: long-term exposure to rain in cold temperatures drives higher thermogenic investment in a captive songbird
Abstract Long-term cold exposure induces many endotherms to invest in metabolic heat production, but how precipitation impacts thermogenic capacity in the context of different thermal conditions is largely undescribed in animals. In this study, songbirds (red crossbills; Loxia curvirostra) were held in warm (21°C) or cold (6°C) temperatures and either dry or rain precipitation treatments while experiencing a more northern or southern latitude photoperiod. We hypothesized that individuals experiencing winter rain would increase investment in thermogenic capacity, metabolic machinery and catabolic enzymes to cope with increased thermogenic demands. Food intake and activity were monitored weekly, summit (Msum) and basal metabolic rates were measured in November, January and February, and tissues were collected at the end of the study. Individuals held in cold rain treatments achieved the highest Msum and had higher food intake, subcutaneous fat, heart mass and metabolic enzyme activities. Furthermore, birds in dry conditions showed slight disinvestment of Msum in late winter, while birds in rain treatments maintained thermogenic investment. Our results suggest that cold rain induces increased investment in thermogenic capacity across the winter season. Thus, rain may offset the potential thermal benefits that warming winters would otherwise provide to small-bodied endotherms.
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- Award ID(s):
- 2224554
- PAR ID:
- 10673011
- Publisher / Repository:
- Royal Society of London
- Date Published:
- Journal Name:
- Royal Society Open Science
- Volume:
- 12
- Issue:
- 12
- ISSN:
- 2054-5703
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1098/rsos.251393
