Body surface rewarming in fully and partially hypothermic king penguins
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ORIGINAL PAPER
Body surface rewarming in fully and partially hypothermic king penguins Agnès Lewden1,2 · Andreas Nord3,4 · Batshéva Bonnet5 · Florent Chauvet5 · André Ancel1 · Dominic J. McCafferty4 Received: 4 November 2019 / Revised: 11 June 2020 / Accepted: 25 June 2020 © The Author(s) 2020
Abstract Penguins face a major thermal transition when returning to land in a hypothermic state after a foraging trip. Uninsulated appendages (flippers and feet) could provide flexible heat exchange during subsequent rewarming. Here, we tested the hypothesis that peripheral vasodilation could be delayed during this recovery stage. To this end, we designed an experiment to examine patterns of surface rewarming in fully hypothermic (the cloaca and peripheral regions (here; flippers, feet and the breast) 0.08), and some birds even appeared to be asleep during measurements (AL, pers. obs.). This effect was, therefore, not considered further below. Mean air temperature, Ta, in the laboratory was 8.1 ± 1.4 °C (s.d.) during all trials (range 4.7–11.4 °C), which is within the thermoneutral zone of king penguins (i.e., − 5 to + 15 °C; Le Maho and Despin 1976; Froget et al. 2002; Fahlman et al. 2004). Of the 16 individuals measured when fully hypothermic in Year 2, 14 were subsequently kept in thermoneutrality in an outdoor roofless wooden enclosure (3 × 3 m) without human disturbance for 68.00 ± 3.00 min to allow rewarming to internal normothermia. These birds were then brought back to the laboratory and thermal images of the flipper and the foot were taken, and Tcloacal (which was 2.2 ± 0.7 °C greater than when the birds had just returned from sea) was recorded. We then briefly immersed all of the body but the head in cold water (ca. 8 °C) that was available from a freshwater supply at the field site. The water bath had similar temperature to seawater in the adjacent bay (7.7 ± 0.9 °C in the same year; Lewden et al. 2017b). Immersion lasted 4.05 min ± 0.25 s, which was enough to induce peripheral vasoconstriction without changing internal temperature. Accordingly, Tcloacal did not differ before (37.3 ± 0.3 °C) and after immersion (37.2 ± 0.2 °C) (paired t test; df = 11
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Journal of Comparative Physiology B
t = − 0.33, P = 0.75), but we observed a significant decrease in Tflipper (before: 16.2 ± 1.4 °C; after: 11.0 ± 0.5 °C) (df = 13 t = − 3.22, P = 0.006), Tfoot (before: 15.8 ± 2.7 °C; after: 10.7 ± 0.5 °C) (df = 8, t = − 0.99, P = 0.035) and Tbreast (before = 15.5 ± 0.8 °C; after = 12.9 ± 0.5 °C) (df = 13 t = − 2.77, P = 0.0101). Birds were then directly returned to the laboratory to be measured a second time (Group 1B, Fig. 1) during 21.0 min ± 0.1 min (range 17.3–25.3 min). The birds were then released in the colony.
Measurements in the colony–Group 2 Thermal imaging of free-ranging birds (N = 24, Fig. 1), which had not been previously measured in the laboratory, was undertaken during Year 2, by following individuals from the point at which they returned from the sea for as long as possible before they could
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