In birds, acclimation and acclimatization to temperature are associated with changes in basal (BMR), summit (Msum) and maximal (MMR) metabolic rates but little is known about the rate at which species adjust their phenotype to short-term temperature variations. Our aims were (1) to determine the pattern of metabolic adjustments following a rapid temperature change, (2) to determine whether performance varies at similar rates during exposure to warm or cold environments, and (3) to determine if BMR, Msum and MMR change at comparable rates during thermal acclimation. We measured these parameters in white-throated sparrows (Zonotrichia albicollis), black-capped chickadees (Poecile atricapillus), and snow buntings (Plectrophenax nivalis) after acclimation to 10 °C (day 0) and on the 4th and 8th days of acclimation to either -5 or 28 °C. Birds changed their metabolic phenotype within 8 days with patterns differing among species. Sparrows expressed the expected metabolic increases in the cold and decreases at thermoneutrality while performance in chickadees and buntings was not influenced by temperature but changed over time with inverse patterns. Our results suggest that BMR varies at comparable rates in warm and cold environments but changes faster than Msum and MMR, likely due to limitations in the rate of change in organ size and function. They also suggest that maximal metabolic capacity is lost faster in a warm environment than it is gained in a cold environment. With the expected increase in temperature stochasticity at northern latitudes, a loss of thermogenic capacity during warm winter days could, therefore, be detrimental if birds are slow to readjust their phenotype with the return of cold days.

No abstract

In winter, temperate resident birds are often faced with periodic low natural food availability. This reduction or unpredictability in resource availability might then have a negative impact on immune function, given that immune system support is highly resource dependent. We investigated the balance between energetic and immune management in captive black-capped chickadees (Poecile atricapilus) by manipulating the predictability of resources. The control group received food ad lib. every day, while the experimental group received a reduced amount of food on random days and food ad lib. on all other days. We measured two key metrics of energetic management (body and fat mass) as well as a suite of immune system components. Compared with control birds, experimental birds maintained significantly higher total body and fat mass, had lower acute phase protein concentrations, and had decreased body temperature and lost more body mass during the fever response following injection with lipopolysaccharides. Interestingly, birds in both groups had similar levels of complement lysis, delayed-type hypersensitivity response (phytohemagglutinin), and primary antibody production (keyhole limpet hemocyanin). This experiment demonstrates that black-capped chickadees strategically increase their fat mass in response to decreased food availability and that this might allow the birds to maintain most of the immune system unaltered, except some of the most costly immune components.

In winter, temperate resident birds are often faced with periodic low natural food availability. This reduction or unpredictability in resource availability might then have a negative impact on immune function, given that immune system support is highly resource dependent. We investigated the balance between energetic and immune management in captive black-capped chickadees (Poecile atricapilus) by manipulating the predictability of resources. The control group received food ad lib. every day, while the experimental group received a reduced amount of food on random days and food ad lib. on all other days. We measured two key metrics of energetic management (body and fat mass) as well as a suite of immune system components. Compared with control birds, experimental birds maintained significantly higher total body and fat mass, had lower acute phase protein concentrations, and had decreased body temperature and lost more body mass during the fever response following injection with lipopolysaccharides. Interestingly, birds in both groups had similar levels of complement lysis, delayed-type hypersensitivity response (phytohemagglutinin), and primary antibody production (keyhole limpet hemocyanin). This experiment demonstrates that black-capped chickadees strategically increase their fat mass in response to decreased food availability and that this might allow the birds to maintain most of the immune system unaltered, except some of the most costly immune components.