One for all and all for one: the energetic benefits of huddling in endotherms

Abstract

Huddling can be defined as "an active and close aggregation of animals". It is a cooperative group behaviour, permitting individuals involved in social thermoregulation to minimize heat loss and thereby lower their energy expenditure, and possibly allowing them to reallocate the saved energy to other functions such as growth or reproduction. Huddling is especially important in the case of animals faced with high heat loss due to a high surface-to-volume ratio, poor insulation, or living in cold environments. Although numerous experimental studies have focused on the huddling behaviour of a wide range of species, to our knowledge, this is the first attempt to review the various implications of this widely used behavioural strategy. Huddling allows individuals to maximise energy savings by (1) decreasing their cold-exposed body surface area, (2) reducing their heat loss through warming of ambient temperatures surrounding the group, and (3) eventually lowering their body temperature through physiological processes. Huddling provides substantial energy savings and is estimated to reduce energy expenditure by between 6 and 53%. Broad variations in the energetic benefits of huddling depend on the number of individuals and species involved in huddles, the ambient temperatures to which individuals are exposed and the density of the aggregations. It has been shown that huddling individuals have increased survival, a lower food intake, a decreased body mass loss, increased growth rate, reduced water loss, and/or a more constant body temperature together with a significant reduction in metabolic rate. Though huddling has been studied widely, this review reveals the intricacies of this adaptive behaviour.

To flock or fight: Neurochemical signatures of divergent life histories in sparrows

“…5). CRH is generally linked to anxiety-like processes and stress (36), which may be the connection to flocking, given that thermoregulatory and foraging challenges lead to facultative grouping in many vertebrate species (37,38). Thus, we might hypothesize that winter flockers are in some sense hyperresponsive to the challenges of winter.…”

Brood size constrains the development of endothermy in blue tits

“…Huddling can also reduce thermal conductance because less of the body surface is exposed to the environment and because huddling may increase ambient temperature in the nest (Gilbert et al, 2010), and the energy saved is due to the decrease in surface area to volume ratio as brood size increases (Mertens, 1969). Consequently, whole broods achieve effective homeothermy much sooner than single nestlings (Dunn, 1976(Dunn, , 1979.…”

“…Consequently, whole broods achieve effective homeothermy much sooner than single nestlings (Dunn, 1976(Dunn, , 1979. It also follows that nestlings in large broods enjoy these thermally advantageous conditions to a greater extent than those in small broods (Dunn, 1976;Gilbert et al, 2010).…”

Energetics of communal roosting in chestnut-crowned babblers: implications for group dynamics and breeding phenology

“…Compensatory physiological responses (adjusted insulation and peripheral blood flow; torpor or hibernation) are well known, but in social species, group behaviour may also be an important component of thermal biology. Huddling or communal roosting occurs in a variety of birds and mammals and has been shown to conserve energy by reducing each individual's resting metabolic rate (extensively reviewed in Du Plessis, 2004;Gilbert et al, 2010). For some species from extreme climates (e.g.…”