Quantifying organismal sensitivity to heat stress provides one means for predicting vulnerability to climate change. Birds are ideal for investigating this approach, as they display quantifiable fitness consequences associated with behavioural and physiological responses to heat stress. We used a recently developed method that examines correlations between readily‐observable behaviours and air temperature (Tair) to investigate interspecific variation in avian responses to heat stress in seasonally hot, arid regions on three continents: the southwestern United States, the Kalahari Desert of southern Africa and the Gascoyne region of western Australia. We found substantial interspecific variation in heat dissipation behaviours (wing‐drooping, panting, activity‐reduction, shade‐seeking) across all three regions. However, pooling the data revealed that little of this interspecific variation was systematically explained by organismal traits (foraging guild, diet, drinking dependency, body mass or activity levels) at the scale we tested. After accounting for phylogeny, we found that larger birds engaged in wing‐drooping behaviour at lower Tair and had lower activity levels at high Tair compared to smaller birds, indicating an effect of body mass on heat dissipation behaviour (HDB). In the Kalahari, reliance on drinking was correlated with significantly lower Tair at which panting commenced, suggesting a key role of water acquisition in HDB in that region. Birds also tended to retreat to shade at relatively lower Tair when more active, suggesting a behavioural trade‐off between activity, heat load and microsite selection. Our results imply that the causes underlying interspecific variation in heat dissipation behaviours are complex. While the variation we observed was not systematically explained by the broad scale organismal traits we considered, we predict that the indices themselves will still reflect vulnerability to potential fitness costs of high air temperatures. Further research is needed on a species‐specific basis to establish the functional significance of these indices.

Nestlings of many bird species are hosts to hematophagous ectoparasites. Parasitism of nestlings is usually sub‐lethal, but its effects can extend into the fledgling and adult stages. Nestling hosts lose enough blood to become anemic, but the effects of reduced oxygen‐carrying capacity on metabolic rate are poorly understood. This study examined the consequences of parasitism by larval blow flies Protocalliphora sialia for nestling tree swallows Tachycineta bicolor. We found that nestlings with more parasites had higher whole‐animal RMR. We evaluated the role of increased erythropoiesis as a potential mechanism explaining increased RMR by drawing blood from some birds. However, we found no evidence that blood loss, as a proxy for hematophagous parasitism, increased metabolic rate. Future work should examine the metabolic costs of upregulation of immunity and how elevated RMR due to ectoparasites affects nestlings as they develop into independent adults.

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Combination fractional laser resurfacing with short flap, high-Superficial muscular aponeurotic system rhytidectomy is a safe procedure with excellent patient satisfaction and clinical outcomes.

Songbirds meet the extreme metabolic demands of migration by burning both stored fat and protein. However, catabolizing these endogenous tissues for energy leads to organ atrophy, and reductions in gastrointestinal tissue can be as great as 50% of the pre-flight mass. Remarkably, during stopover refuelling birds quickly regain digestive mass and performance. Aminopeptidase-N (APN) is a brush-border enzyme responsible for late-stage protein digestion and may critically assist tissue reconstruction during the stopover, thus compensating for reduced gut size. We hypothesized that birds recovering from a fast would differentially upregulate APN activity relative to disaccharidases to rapidly process and assimilate dietary protein into lean mass. We fasted 23 wild-caught migratory white-throated sparrows ( Zonotrichia albicollis ) for 48 h to mimic mass reductions experienced during migratory flight and measured intestinal APN activity before the fast, immediately after the fast, and during recovery at 24 h and 48 h post-fast. Total fat mass, lean mass and basal metabolic rate were measured daily. We show that fasted birds maintain APN activity through the fast, despite a 30% reduction in intestine mass, but during refuelling, APN activity increases nearly twofold over pre-fasted individuals. This suggests that dynamically regulating APN may be necessary for rapid protein reconstruction during the stopover.