Energy saving processes in huddling emperor penguins: from experiments to theory

Abstract

SummaryThis paper investigates the energy savings of male emperor penguins Aptenodytes forsteri linked to their huddling behaviour, the key factor that allows them to assume their incubating task while undergoing a long fast. Drawing on new studies by our team, this review examines the energetic benefits accrued from huddling and estimates the respective contributions of wind protection, exposure to mild ambient temperatures, reduction in cold-exposed body surfaces and body temperature adjustments in these energy savings. The metabolic rate of ʻloosely groupedʼ birds (restrained in small groups of 5-10 individuals, which are unable to huddle effectively) is reduced by 39% compared to metabolic rate of ʻisolatedʼ birds, with 32% of these energetic benefits due to wind protection. In addition, metabolic rate of ʻfree-rangingʼ emperors, i.e. able to move freely and to huddle, is on average 21% lower than that of ʻloosely groupedʼ birds. Exposure to mild ambient temperatures within the groups and reduction in coldexposed body surfaces while huddling, though overestimated, would represent a 38% metabolic reduction. About two thirds of metabolic lowering is attributable to the reduction in cold-exposed body surfaces and one third to the mild microclimate created within the groups. Moreover, body temperature adjustments contribute to these energetic benefits: maintaining body temperatures 1°C lower would represent a 7-17% reduction in energy expenditure. These processes, linked together, explain how huddling emperors save energy and maintain a constant body temperature, which ensures a successful incubation in the midst of the austral winter.

Fasting Therapy - an Expert Panel Update of the 2002 Consensus Guidelines

“…Migratory birds fast during migration while engaging in intensive physical activity. Other animals reduce their energy consumption by entering lethargic states (hibernation) [25,26]. King penguins fast - in the Antarctic cold - for extremely long periods and can lay their eggs and molt while fasting [27].…”

Synchronous activity lowers the energetic cost of nest escape for sea turtle hatchlings

“…Experimental data from a broad range of taxa show that there are at least four mutual benefits that can result from aggregation behaviour: (i) decreased chance of predation (Colbert et al, 2010;Creel et al, 2014;Unglaub et al, 2013), (ii) increased feeding efficiency (Horst, 1995;Jackson et al, 2008;Hsia and Wood-Gush, 1982;Lazarus, 1979), (iii) increased locomotion efficiency (Ebensperger and Bozinovic, 2000;Fish, 1995;Voelkl et al, 2015) and (iv) decreased energy spent on thermoregulation (Gilbert et al, 2008(Gilbert et al, , 2010Nunez-Villegas et al, 2014;Withers and Jarvis, 1980). However, aggregation behaviour may have more than one function within a single species (Lazarus, 1979).…”

Huddling behavior as critical phase transition triggered by low temperatures

“…Thermoregulatory huddling has developed in several taxonomic groups, including small mammals, birds, reptiles, and insects. Convergence of huddling behavior among animals is a fascinating evolutionary event, emperor penguins being a notable case [13,14]. In small mammals, huddling appears as an efficient response to low temperature with important consequences in energy saving and allocation of energy, which in turn affect the survival, rates of food ingestion, and individual fitness [15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”