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Technological advancements now enable the use of flow-through respirometry for rapid, high-throughput metabolic phenotyping, though live-in systems currently do not exist for birds. We designed live-in respirometry chambers for small birds with an Arduino-based electronic system to continuously monitor bird body weight, food intake, and water intake in sync with metabolic data collection. To demonstrate how this system can be implemented, we kept birds in the metabolic phenotypic chambers for 10 days while we progressively lowered the temperature from 25 °C to 5 °C. We used the data to calculate hourly energy expenditure and food/water intake during acute cold acclimation. We provide all plans and code for the live-in chambers, Arduino biomonitoring system, and additional RFID module as a low-cost, DIY alternative to commercially available systems and to enable the use of standard respirometry equipment for metabolic phenotyping in birds. 

Abstract BackgroundEcological barriers can shape the movement strategies of migratory animals that navigate around or across them, creating migratory divides. Wind plays a large role in facilitating aerial migrations and can temporally or spatially change the challenge posed by an ecological barrier, with beneficial winds potentially converting a barrier into a corridor. Here, we explore the role wind plays in shaping initial southbound migration strategy among individuals breeding at two sites along an ecological barrier. MethodsUsing GPS satellite transmitters, we tracked the southbound migrations of Short-billed Dowitchers(Limnodromus griseus caurinus)from two breeding sites in Alaska to nonbreeding sites in coastal Mexico. The breeding sites were positioned in distinct regions along an ecological barrier – the Gulf of Alaska. We investigated potential differences in migratory timing, wind availability, and tailwind supportenroute across the Gulf of Alaska between individuals breeding at the two sites. ResultsRoute choice and arrival timing to wintering sites differed markedly between the two breeding sites: individuals departing from the more westerly site left at the same time as those from further east but crossed the Gulf of Alaska farther west and arrived along the Pacific coast of Mexico an average of 19 days earlier than their counterparts. Dowitchers from both sites departed with slight tailwinds, but once aloft over the Gulf of Alaska, birds from the more westerly site had up to twelve times more tailwind assistance than birds from the more easterly one. ConclusionsThe distinct migration strategies and degree of wind assistance experienced by birds at these two breeding sites demonstrates how differences in wind availability along migratory routes can form the basis for intraspecific variation in migration strategies with potential carryover effects. Future changes in wind regimes may therefore interact with changes in habitat availability to influence migration patterns and migratory bird conservation. 

Synopsis Endothermic species have evolved strategies to maximize survival in highly variable or extreme environments. Birds are exemplary as they are among the most widely distributed endotherms on the planet, living in all manner of inhospitable environments. As an example, winter in temperate regions is characterized by cold temperatures and low food availability. Some birds have evolved to tolerate these conditions by seasonally increasing thermogenic capacity, increasing heterothermy, and displaying highly flexible phenotypes. Other species have evolved to avoid the inhospitable conditions of winter altogether by migrating—again requiring a unique set of physiological adaptations that allow success in this challenging endeavor. In these examples and in many others, the organismal requirements for success share similarities, but the underlying mechanisms, physiological requirements, and selection on those traits can differ significantly, as can their ecological and evolutionary impacts. In recent years, a suite of novel and established tools has become widely available and more accessible, allowing insights into long-standing questions. Genomic tools, new approaches to measure organismal performance, the use of citizen science data, easier access to metabolite assays or hormone detection, to name a few, have spurred rapid advances in our understanding of avian physiology. These new tools have been leveraged to investigate important questions regarding avian responses to our rapidly changing climate in an attempt to understand species resilience and limits. 

Synopsis Homeothermic endotherms defend their body temperature in cold environments using a number of behavioral and physiological mechanisms. Maintaining a stable body temperature primarily requires heat production through shivering or non-shivering thermogenesis (NST). Although the use of NST is well established in mammalian systems, the mechanisms and extent to which NST is used in birds are poorly understood. In mammals, one well-characterized mechanism of NST is through uncoupling of Ca2+ transport from ATP hydrolysis by sarco/endoplasmic reticulum ATPase (SERCA) in the skeletal muscle, which generates heat and may contribute to Ca2+ signaling for fatigue resistance and mitochondrial biogenesis. Two small proteins—sarcolipin (SLN) and phospholamban (PLN)—are known to regulate SERCA in mammals, but recent work shows inconsistent responses of SLN to cold acclimation in birds. In this study, we measured SERCA uncoupling in the pectoralis flight muscle of control (18°C) and cold-acclimated (−8°C) dark-eyed juncos (Junco hyemalis) that exhibited suppressed SLN transcription in the cold. We measured SERCA activity and Ca2+ uptake rates for the first time in cold-acclimated birds and found greater SERCA uncoupling in the muscle of juncos in the cold. However, SERCA uncoupling was not related to SLN or PLN transcription or measures of mitochondrial biogenesis. Nonetheless, SERCA uncoupling reduced an individual’s risk of hypothermia in the cold. Therefore, while SERCA uncoupling in the cold could be indicative of NST, it does not appear to be mediated by known regulatory proteins in these birds. These results prompt interesting questions about the significance of SLN and PLN in birds and the role of SERCA uncoupling in response to environmental conditions. 

SUMMARY With rapid environmental change, shifts in migration timing are vitally important for maintaining population stability and have been widely documented. However, little remains known abouthowmigrants are driving these shifts and what factors may influence the effective utilization of these strategies, limiting our ability to accurately assess species- and population-level vulnerability to climate change. The Hudsonian godwit (Limosa haemastica) is an extreme long-distance migratory shorebird that has (1) previously shifted its population-level migration timing and (2) exhibits sex-specific morphological differences. Therefore, we combined over a decade of light-level geolocator tracking data from a single breeding population with a historical predictive model to assess on-going shifts in migration timing while determining the time-shifting strategies utilized by each sex. Surprisingly, we found that godwit departure and arrival timing rapidly shifted 6 days later from 2010-2023 with no differences in timing between the sexes. Despite this change in migration timing, the population has maintained an average migratory duration of 24 days, suggesting that godwits are driving shifts in arrival timing entirely by shifting their nonbreeding ground departure, something rarely documented in long-distance migrants. Yet, we also found that godwits are not shifting their migration timing in the direction predicted by our model, providing evidence that this response may not be adaptive. These results emphasize the urgent need for a more holistic approach to assessing the relative vulnerability of migratory species and the adaptiveness of changes in migration timing. 

Abstract Reversible phenotypic flexibility allows organisms to better match phenotypes to prevailing environmental conditions and may produce fitness benefits. Costs and constraints of phenotypic flexibility may limit the capacity for flexible responses but are not well understood nor documented. Costs could include expenses associated with maintaining the flexible system or with generating the flexible response. One potential cost of maintaining a flexible system is an energetic cost reflected in the basal metabolic rate (BMR), with elevated BMR in individuals with more flexible metabolic responses. We accessed data from thermal acclimation studies of birds where BMR and/or M_sum(maximum cold-induced metabolic rate) were measured before and after acclimation, as a measure of metabolic flexibility, to test the hypothesis that flexibility in BMR (ΔBMR), M_sum(ΔM_sum), or metabolic scope (M_sum − BMR; ΔScope) is positively correlated with BMR. When temperature treatments lasted at least three weeks, three of six species showed significant positive correlations between ΔBMR and BMR, one species showed a significant negative correlation, and two species showed no significant correlation. ΔM_sumand BMR were not significantly correlated for any species and ΔScope and BMR were significantly positively correlated for only one species. These data suggest that support costs exist for maintaining high BMR flexibility for some bird species, but high flexibility in M_sumor metabolic scope does not generally incur elevated maintenance costs. 

Abstract Elevations >2,000 m represent consistently harsh environments for small endotherms because of abiotic stressors such as cold temperatures and hypoxia.These environmental stressors may limit the ability of populations living at these elevations to respond to biotic selection pressures—such as parasites or pathogens—that in other environmental contexts would impose only minimal energetic‐ and fitness‐related costs.We studied deer mice (Peromyscus maniculatus rufinus) living along two elevational transects (2,300–4,400 m) in the Colorado Rockies and found that infection prevalence by botfly larvae (Cuterebridae) declined at higher elevations. We found no evidence of infections at elevations >2,400 m, but that 33.6% of all deer mice, and 52.2% of adults, were infected at elevations <2,400 m.Botfly infections were associated with reductions in haematocrit levels of 23%, haemoglobin concentrations of 27% and cold‐induced VO_2maxmeasures of 19% compared to uninfected individuals. In turn, these reductions in aerobic performance appeared to influence fitness, as infected individuals exhibited 19‐34% lower daily survival rates.In contrast to studies at lower elevations, we found evidence indicating that botfly infections influence the aerobic capabilities and fitness of deer mice living at elevations between 2,000 and 2,400 m. Our results therefore suggest that the interaction between botflies and small rodents is likely highly context‐dependent and that, more generally, high‐elevation populations may be susceptible to additional biotic selection pressures. Aplain language summaryis available for this article.