C. Carbone et al., ADJUSTMENTS IN THE DIVING TIME BUDGETS OF TUFTED DUCK AND POCHARD - IS THERE EVIDENCE FOR A MIX OF METABOLIC PATHWAYS, Animal behaviour, 51, 1996, pp. 1257-1268
Predictions of models for the optimal allocation of time over the dive
cycle for divers using aerobic and anaerobic respiration, were tested
experimentally on the tufted duck, Aythya fuligula, and pochard, A. f
erina. Patterns in the dive cycle were highly correlated with water de
pth. In both species, foraging time increased with water depth up to 3
m. In the pochard, foraging time subsequently declined before increas
ing again at around 4 m. Qualitatively similar patterns in foraging ti
me are predicted by the model based on the use of aerobic and anaerobi
c respiration, the 'mixed metabolism' model. As predicted by this mode
l and previous 'aerobic' models, foraging time decreased in response t
o increasing substrate depth (used to increase foraging costs), while
surface time was not affected. Paddle rates, used as an indicator of f
oraging costs, however, did not increase. In response to lower water t
emperature (used to increase the energetic costs of both the travel an
d foraging phases of the dive), surface times increased as predicted,
except at the shallowest depth class. The predicted relationship betwe
en foraging time and diving costs is complex, being dependent on water
depth and a number of other parameters; the observed trends were non-
significant. Ascent duration decreased with decreasing temperature, bu
t descent duration did not change significantly. Estimates of paddle r
ates and travel speeds suggest that foraging is on average more costly
than travelling (ascent and descent combined), diving costs decrease
with depth and travel speeds change subtly with depth. (C) 1996 The As
sociation for the Study of Animal Behaviour