Aestivation in Mammals and Birds

Abstract

Aestivation, which in the context of this paper refers to avian and mammalian torpor in summer/at high ambient temperatures (T (a)), does not appear to differ functionally from other forms of torpor, and to a large extent reflects the higher body temperatures (T (b)) caused by high T (a). However, from an ecological point of view, aestivation results in different challenges and requirements than does torpor use in winter, because heat can cause reduced food and water availability in many regions, but without the access to low T (a) for a substantial reduction of T (b). Aestivation is used by a diversity of adult mammals and birds both in the field and laboratory, as well as by growing young to reduce thermoregulatory energy expenditure. Torpor occurs at high T (a) including the thermo-neutral zone and even under these conditions the reduction in energy expenditure and water requirements or water loss is substantial. Although data from the laboratory and, especially, from the field are limited, they show that torpor at high T (a) is an effective survival strategy and suggest that it is employed by many mammals and birds in a diversity of habitats.

Integrative Physiology of Fasting

“…The echidna Tachyglossus aculeatus, pygmy possums (Cercartetus), bats, assorted rodents, and several birds including poorwills (Phalaenoptilus nuttallii), nightjars (Eurostopodus argus), and Andean hummingbirds (Oreotrochilus estella) have all been documented to employ short bouts of torpor during the summer (210). The distinction between estivation and hibernation is fluid, and some species, such as the edible dormouse, Glis glis, is capable of hibernation in winter, estivation in summer, and daily torpor throughout the year when food is limited (582).…”

“…For birds and mammals, the term estivation is commonly used synonymously with summer torpor, both generally brief in duration (∼24 h) (210). The echidna Tachyglossus aculeatus, pygmy possums (Cercartetus), bats, assorted rodents, and several birds including poorwills (Phalaenoptilus nuttallii), nightjars (Eurostopodus argus), and Andean hummingbirds (Oreotrochilus estella) have all been documented to employ short bouts of torpor during the summer (210).…”

Dietary restriction and insulin‐like signalling pathways as adaptive plasticity: A synthesis and re‐evaluation

“…Animals in habitats that do not have large photoperiodic shifts, or in environments where photoperiodicity does not predict seasonal change such as wet/dry, need to time life-history events using other cues. In arid environments where water is limiting, animals modify their metabolism and transition to reproductive arrest during dry periods (Geiser, 2010), for example, the desert-dwelling golden spiny mouse, responds to dietary salinity to repress reproduction, via vasopressin (Shanas & Haim, 2004), which is known to respond to insulin and blood glucose levels (Nakamura, Velho, & Bouby, 2017).…”

Characterizing the reproductive transcriptomic correlates of acute dehydration in males in the desert-adapted rodent, Peromyscus eremicus

“…Examples of well-described desert mammal behavioral adaptations are seasonal torpor (reviewed in [15, 16]), nocturnality (e.g. [17, 18]) and burrowing (reviewed in [19, 20]) to avoid high temperatures and sun exposure.…”