Adaptations to polar life in mammals and birds

Abstract

This Review presents a broad overview of adaptations of truly Arctic and Antarctic mammals and birds to the challenges of polar life. The polar environment may be characterized by grisly cold, scarcity of food and darkness in winter, and lush conditions and continuous light in summer. Resident animals cope with these changes by behavioural, physical and physiological means. These include responses aimed at reducing exposure, such as 'balling up', huddling and shelter building; seasonal changes in insulation by fur, plumage and blubber; and circulatory adjustments aimed at preservation of core temperature, to which end the periphery and extremities are cooled to increase insulation. Newborn altricial animals have profound tolerance to hypothermia, but depend on parental care for warmth, whereas precocial mammals are well insulated and respond to cold with non-shivering thermogenesis in brown adipose tissue, and precocial birds shiver to produce heat. Most polar animals prepare themselves for shortness of food during winter by the deposition of large amounts of fat in times of plenty during autumn. These deposits are governed by a sliding set-point for body fatness throughout winter so that they last until the sun reappears in spring. Polar animals are, like most others, primarily active during the light part of the day, but when the sun never sets in summer and darkness prevails during winter, high-latitude animals become intermittently active around the clock, allowing opportunistic feeding at all times. The importance of understanding the needs of the individuals of a species to understand the responses of populations in times of climate change is emphasized.

Heat dissipation rate constrains reproductive investment in a wild bird

“…It is interesting to note that such constraints may even be present in a small animal with inherently high thermal conductance (Aschoff, 1981) in a relatively cold habitat. Future studies should address how these costs manifest over latitudinal gradients, from southern species in arid climes that are close to their thermal tolerance limits (Nilsson, Molokwu, & Olsson, 2016) to subarctic and Arctic species where low thermal conductance is key to survival (Blix, 2016) and increased heat dissipation might be undesirable (cf. Szafrańska et al, 2014;Nord & Folkow, 2018).…”

Function and underlying mechanisms of seasonal colour moulting in mammals and birds: what keeps them changing in a warming world?

“…Species occupying temperate and polar latitudes have multiple physiological and life‐history adaptations that help them cope with harsh winters and high seasonality (Blix, ). Those circannual traits include seasonal migration, hibernation and coat colour moults, and their occurrence and optimal phenology is critical for maintaining fitness (Varpe, ).…”

Seasonal variation in the thermal responses to changing environmental temperature in the world's northernmost landbird

“…fat deposition and thermoregulatory responses such as peripheral vasoconstriction, respiratory responses, shivering thermogenesis, etc. ; reviewed by Blix, 2016).…”