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Heart rate as an indicator of oxygen consumption: influence of body condition in the king penguin

G. Froget^1,2,*, P. J. Butler¹, Y. Handrich² and A. J. Woakes¹

¹ School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK and
² Centre d’Ecologie et Physiologie Energétiques, C.N.R.S., 23 rue Becquerel, 67087 Strasbourg Cedex 02, France

View larger version (24K): [in a new window]   Fig. 1. Breeding cycle of an average king penguin on Crozet Island (adapted from Barrat, 1976). Incubation or chick rearing/guarding shifts ashore (hatched areas) are alternated with foraging shifts at sea (filled areas) and decrease in duration through the cycle. Sx denotes the shift number.

View larger version (21K): [in a new window]   Fig. 2. Diagram of the open-circuit system used to measure oxygen consumption and carbon dioxide production in king penguins walking at different speeds.

View larger version (14K): [in a new window]   Fig. 3. Mean heart rate (fH, A), rate of oxygen of consumption (O2, B) and mass-specific O2 (sO2, C) of 22 king penguins walking at different speeds on a treadmill. The birds are in four groups, females (squares, N=5, FD) and males (circles, N=5, MD) departing from the colony and females (triangles, N=6, FA) and males (crosses, N=6, MA) arriving at the colony after a foraging shift. The vertical and horizontal lines at each point represent ± S.E.M.

View larger version (9K): [in a new window]   Fig. 4. Resting individual oxygen pulse (ROP, circles) and active oxygen pulse (AOP, squares) for 22 king penguins plotted against the nutritional index NI (see text for details). The continuous line is the regression line between ROP and NI (ROP=1.0326+0.1761NI, r2=0.36, P=0.004), and the broken line is the regression line between AOP and NI (AOP=1.5637+0.36NI, r2=0.46, P=0.0007).

View larger version (10K): [in a new window]   Fig. 5. Graphical representation of the three different models used to estimate the rate of oxygen consumption O2 from heart rate fH in a hypothetical arriving male with a bill length of 123.8mm and a body mass of 12.2kg (nutritional index NI=3.2). The grey line represents the general linear regression model (GLR) for departing males, the broken lines use a combination of resting oxygen pulse (ROP) (from minimum resting fH, , to maximum resting fH, R) and the linear regression for the birds walking on the treadmill (from minimum exercising fH, , to maximum walking fH, ). The solid black lines represent the model using ROPs and active oxygen pulses (AOPs) as function of the nutritional index (NI).

View larger version (14K): [in a new window]   Fig. 6. Distribution of the absolute error between 30min estimates of oxygen consumption rate O2 and measured O2 for the six calibrations obtained using the general linear regression model (model i, grey line) when using a combination of resting oxygen pulse (ROP) and the linear regression for the birds walking on the treadmill (model ii, broken line) or when ROPs and active oxygen pulses (AOPs) are expressed as function of the nutritional index (model iii, black line). The horizontal dashed line is the line of 75% of the total errors of 30min estimates, and the arrows indicate the respective error for each model (75% of errors are below 34% when using model i, below 26% when using model ii and below 20% when using model iii).

View larger version (8K): [in a new window]   Fig. 7. Double logarithmic plot of E against body mass (BM, kg), where E is the energy cost of walking (in lO2kg-1km-1). Data for the emperor penguin (EP), the Adélie penguin (AP) and the white-flippered penguin (WfP) are derived from Pinshow et al. (Pinshow et al., 1976), data for the little penguin (LP) are derived from Baudinette and Gill (Baudinette and Gill, 1985), data for the gentoo penguin (GP) are derived from Bevan et al. (Bevan et al., 1995), data for the macaroni penguin (MP) are from Green et al. (Green et al., 2001) and data for king penguin (KP) data are from the present study. The dotted line is the regression line for all penguins other than the king penguin: logE=-0.3822logBM+0.3477, r2=0.9637, P<0.003, N=6). The solid line is the line calculated for running mammals: logE=-0.4434logBM+0.5057 (Taylor et al., 1970).