Fat King Penguins Are Less Steady on Their Feet
Résumé
Returning to the shore after a feeding sojourn at sea, king penguins often undertake a relatively
long terrestrial journey to the breeding colony carrying a heavy, mostly frontal, accumulation
of fat along with food in the stomach for chick-provisioning. There they must
survive a fasting period of up to a month in duration, during which their complete reliance on
endogenous energy stores results in a dramatic loss in body mass. Our aim was to determine
if the king penguin’s walking gait changes with variations in body mass.We investigated
this by walking king penguins on a treadmill while instrumented with an acceleration
data logger. The stride frequency, dynamic body acceleration (DBA) and posture of fat (prefasting;
13.2 kg) and slim (post fasting; 11 kg) king penguins were assessed while they
walked at the same speed (1.4km/h) on a treadmill. Paired statistical tests indicated no evidence
for a difference in dynamic body acceleration or stride frequency between the two
body masses however there was substantially less variability in both leaning angle and the
leaning amplitude of the body when the birds were slimmer. Furthermore, there was some
evidence that the slimmer birds exhibited a decrease in waddling amplitude. We suggest
the increase in variability of both leaning angle and amplitude, as well as a possibly greater
variability in the waddling amplitude, is likely to result from the frontal fat accumulation when
the birds are heavier, which may move the centre of mass anteriorly, resulting in a less stable
upright posture. This study is the first to use accelerometry to better understand the gait
of a species within a specific ecological context: the considerable body mass change exhibited
by king penguins.
Domaines
Sciences de l'environnement
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