It Takes Time to Be Cool: On the Relationship between Hyperthermia and Body Cooling in a Migrating Seaduck

Abstract

The large amount of energy expended during flapping flight is associated with heat generated through the increased work of the flight muscles. This increased muscle work rate can manifest itself in core body temperature (Tb) increase of 1–2°C in birds during flight. Therefore, episodic body cooling may be mandatory in migratory birds. To elucidate the thermoregulatory strategy of a short-distance migrant, common eiders (Somateria mollissima), we implanted data loggers in the body cavity of wild birds for 1 year, and report information on Tb during their entire migration for 19 individuals. We show that the mean body temperature during flight (TbMean) in the eiders was associated with rises in Tb ranging from 0.2 to 1.5°C, largely depending on flight duration. To understand how eiders are dealing with hyperthermia during migration, we first compare, at a daily scale, how Tb differs during migration using a before-after approach. Only a slight difference was found (0.05°C) between the after (40.30°C), the before (40.41°C) and the migration (40.36°C) periods, indicating that hyperthermia during flight had minimal impact at this time scale. Analyses at the scale of a flight cycle (flight plus stops on the water), however, clearly shows that eiders were closely regulating Tb during migration, as the relationship between the storage of heat during flight was highly correlated (slope = 1) with the level of heat dumping during stops, at both inter-individual and intra-individual levels. Because Tb at the start of a flight (TbStart) was significantly and positively related to Tb at the end of a flight (TbEnd), and the maximal attained Tb during a flight (TbMax), we conclude that in absence of sufficient body cooling during stopovers, eiders are likely to become increasingly hyperthermic during migration. Finally, we quantified the time spent cooling down during migration to be 36% of their daily (24 h) time budget, and conclude that behavioral body cooling in relation to hyperthermia represents an important time cost.

Egg-laying increases body temperature to an annual maximum in a wild bird

“…This is especially true when "natural" thermal boundaries of the annual cycle and reproduction coincide, as shown in female Common eiders in this study. For example, average peak Tb while laying eggs (ranging from 41.3 to 41.6 °C for about 20 min, Fig.S2) compared with intense locomotion during migratory flights (approximately 41.5 °C on average for flights > 80 min 96 ), in the same individuals as in this study, is similar. However, migrating eiders limited the development of flying-induced hyperthermia by landing on the water surface regularly to cool down 96 .…”

Limited heat tolerance in a cold-adapted seabird: implications of a warming Arctic

“…While we measured the effects of warmer temperatures on resting murres, further investigation should consider the impacts of heat stress during high energy behaviours, as endotherms are limited in the maximal energy they can expend by their ability to dissipate heat (Speakman and Król, 2010). For example, common eiders (Somateria mollissima) experience hyperthermia during flight and must stop to cool down, which is a major cost of migration (Guillemette et al, 2016(Guillemette et al, , 2017. As murres are large seabirds with high energetic costs of flight (Elliott et al, 2013b) and high daily energy requirements (Elliott and Gaston, 2014), their low heat tolerance may lead to energetic trade-offs to support their high costs of thermoregulation, which may impact their behaviour, reproductive success and, ultimately, survival.…”

Tackling the Tibetan Plateau in a down suit: insights into thermoregulation by bar-headed geese during migration

“…However, hyperthermia in pigeons may not be directly comparable with that of wild migrating birds, as it was recorded in wind tunnels where flight durations are often shorter than in free-flying birds (Bishop et al, 2002). Furthermore, eider ducks, which are a diving species, may be more susceptible to hyperthermia than bar-headed geese not only because of their diving behaviour but also because of their high body weight to wing area ratio that increases flight costs (Guillemette et al, 2017). Eider ducks migrate in a series of short flights across bodies of ocean where they can land and offload heat via increased blood flow to the legs in the water (Kilgore and Schmidt-Nielsen, 1975), and while resting are protected by effective down insulation.…”

“…There are a number of physiological maladjustments that excessive heat gain might cause, including damage to enzymes, increased oxidative stress and dehydration (Dawson, 1982;McKechnie and Wolf, 2019). Sufficient heat can be generated during flight to reduce flight duration to 15 min in migrating eider ducks (Somateria mollissima), a predominantly diving species (Guillemette et al, 2016), and necessitate periods of cooling following these flights (Guillemette et al, 2017). Bar-headed geese can complete long flights of up to 8 h (Hawkes et al, 2011), suggesting they may not be constrained in such a way, nor spend large periods of time cooling after flight.…”