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First published online November 4, 2005
Journal of Experimental Biology 208, 4231-4241 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01884

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Year-round recordings of behavioural and physiological parameters reveal the survival strategy of a poorly insulated diving endotherm during the Arctic winter

David Grémillet^1,*, Grégoire Kuntz^1,2, Anthony J. Woakes³, Caroline Gilbert^1,2, Jean-Patrice Robin¹, Yvon Le Maho¹ and Patrick J. Butler³

¹ Centre d'Ecologie et Physiologie Energétiques, Centre National de la Recherche Scientifique, 23 Rue Becquerel, 67087 Strasbourg Cedex 02, France
² French Polar Institute Paul-Emile Victor, Technopôle Brest-Iroise, BP 75-29280 Plouzané, France
³ School of Biosciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

View larger version (23K): [in a new window]   Fig. 1. (A) Dive patterns, (B) heart rate and (C) abdominal temperature of a male great cormorant on Christmas Day 2002 in West Greenland (i.e. during the polar night). Heart rate is maximum when the bird is at the water surface (1), but decreases sharply during dives (2). Sustained heart rates >200 beats min-1 in the absence of diving activity occur during flight (3). Note that the abdominal temperature of the bird decreases gradually during the dive bout (T), to reach a minimum after completion of the dive series (4). This short-term temperature drop is probably linked to combined effects of diving in cold water and of ingesting cold fish.

View larger version (29K): [in a new window]   Fig. 2. Daily foraging effort of Greenland great cormorants throughout the annual cycle., showing one data point every second day; values are means + S.D. (N=3-7). The continuous line shows day length (h). The four phases of the year cycle (chick-rearing, wintering, mating and incubating) were defined after Salomonsen (1967) and Lyngs (2003).

View larger version (22K): [in a new window]   Fig. 3. Dive depths of Greenland great cormorants throughout the year cycle, showing one data point every eighth day; values are means ± S.D. (N=3-7).

View larger version (25K): [in a new window]   Fig. 4. (A) Abdominal temperatures in resting Greenland great cormorants throughout the year cycle. Filled circles, abdominal temperatures of animals resting during the non-active phase (02:00-05:00 h); empty circles, abdominal temperatures of animals resting during the active phase (10:00-15:00 h). One data point is shown every eighth day; values are means + S.D. (N=3-7). (B) Abdominal temperatures of foraging Greenland great cormorants throughout the year cycle. Filled circles, abdominal temperatures of diving animals; empty circles, abdominal temperatures of animals after a diving sequence. One data point is shown every eighth day; values are means + S.D. (N=3-7). (C) Effect of diving on the abdominal temperature of Greenland great cormorants throughout the year cycle. T was measured between the moment of the first and the last dive within the dive series. One data point is shown every eighth day; values are means + S.D. (N=3-7).

View larger version (29K): [in a new window]   Fig. 5. (A) Heart rate of foraging Greenland great cormorants throughout the year cycle. Filled circles, heart rate (HR) of birds at the water surface in-between dives; empty circles, heart rate of birds in the deepest section of dives. The latter are also the lowest heart rates during the dives. One data point is shown every eighth day; values are means + S.D. (N=3-7). (B) Heart rate of resting Greenland great cormorants throughout the year cycle. Filled circles, heart rates of animals resting during the non-active phase (2:00-5:00 h); empty circles, heart rates of animals resting during the active phase (10:00-15:00 h). One data point is shown every eighth day; values are means + S.D. (N=3-7).

View larger version (13K): [in a new window]   Fig. 6. Positive relationship between theoretical foraging efficiency [Catch per unit effort (CPUE) in g fish caught min-1 spent underwater] and day length in great cormorants wintering in Greenland (September to April). CPUE was modelled after Grémillet et al. (2003) using field data collected during this study as time budget input values. y=2.04x+24.95.