Heart rate (fH), abdominal temperature (Tab) and diving
depth were measured in thirteen free-ranging breeding
female macaroni penguins. Measurement of these
variables allowed estimation of the mass-specific rate of
oxygen consumption (V˙O·) while diving and investigation
of the physiological adjustments that might facilitate the
diving behaviour observed in this species. In common with
other diving birds, macaroni penguins showed significant
changes in fH associated with diving, and these variables
accounted for 36% of the variation in dive duration.
When V˙O· was calculated for dives of different durations,
95.3% of dives measured were within the calculated
aerobic dive limit (cADL) for this species. Mean fH for all
complete dive cycles was 147±6 beats min–1. When this fH
is used to estimate V˙O· of 26.2±1.4 ml min–1 kg–1 then
only 92.8% of dives measured were within the cADL.
Significant changes in abdominal temperature were not
detected within individual dives, though the time constant
of the measuring device used may not have been low enough to record these changes if they were present.
Abdominal temperature did decline consistently during
bouts of repeated diving of all durations and the mean
decrease in Tab during a diving bout was 2.32±0.2°C.
There was a linear relationship between bout duration
and the magnitude of this temperature drop. There was no
commensurate increase in dive duration during dive bouts
as Tab declined, suggesting that macaroni penguins are
diving within their physiological limits and that factors
other than Tab are important in determining the duration
of dives and dive bouts. Lowered Tab will in turn facilitate
lower metabolic rates during diving bouts, but it was not
possible in the present study to determine the importance
of this energy saving and whether it is occurs actively or
passively.