Proportion Of Dives Research Articles

REGULATION OF TRIP DURATION BY AN INSHORE FORAGER, THE LITTLE PENGUIN (EUDYPTULA MINOR), DURING INCUBATION

Abstract Both sexes of central-place-foraging seabirds usually share the task of incubation and alternate fasting bouts on the egg with foraging trips at sea. Because foraging strategies during incubation are poorly known, compared with strategies during chick rearing, we examined the foraging behavior of incubating Little Penguins (Eudyptula minor), together with nest-attendance behavior. The duration of foraging trips varied greatly (1–9 days). Birds with lower initial body condition made longer foraging trips, and the increase in body condition after multi-day trips was higher than that after single-day trips. During trips of >1 day, females dove more times each day but total underwater time did not differ between the sexes. By contrast, during one-day trips, foraging males made as many dives as females and spent more time underwater. Birds making longer trips spent more time diving on the second day than on the first day. The proportion of dives in which prey was encountered was lower during single-da...

Do seasonal changes in metabolic rate facilitate changes in diving behaviour?

Macaroni penguins were implanted with data loggers to record heart rate (fH), abdominal temperature (Tab) and diving depth during their pre-moult trip (summer) and winter migration. The penguins showed substantial differences in diving behaviour between the seasons. During winter, mean and maximum dive duration and dive depth were significantly greater than during summer, but the proportion of dives within the calculated aerobic dive limit (cADL) did not change. Rates of oxygen consumption were estimated from fH. As winter progressed, the rate of oxygen consumption during dive cycles (sVO2DC)) declined significantly and mirrored the pattern of increase in maximum duration and depth. The decline in sVO2DC) was matched by a decline in minimum rate of oxygen consumption (sVO2min)). When sVO2min) was subtracted from sVO2DC), the net cost of diving was unchanged between summer and winter. We suggest that the increased diving capacity demonstrated during the winter was facilitated by the decrease in sVO2min). Abdominal temperature declined during winter but this was not sufficient to explain the decline in sVO2min). A simple model of the interactions between sVO2min), thermal conductance and water temperature shows how a change in the distribution of fat stores and therefore a change in insulation and/or a difference in foraging location during winter could account for the observed reduction in sVO2min) and hence sVO2DC).

Diving development in nursing harbour seal pups.

This study investigated physiological and behavioural aspects of diving development in pups of the harbour seal Phoca vitulina. Behavioural data (4280 h, 6027 dives) from time/depth recorders (N=13) deployed on pups aged 0-19 days are presented concomitantly with physiological measurements (N=8, sampled both early and late in the nursing period) of blood oxygen stores and body composition. Pups grew from 12.6+/-1.8 kg (mean age 2 days, total body fat 16+/-4 %) to 22.2+/-2.5 kg (mean age 16 days, total body fat 35+/-5 %; means +/- S.D.) over the duration of the experiment. Pups less than 5 days of age had an elevated haematocrit and reduced plasma volume compared with older pups. Although plasma volume and blood volume increased, mass-specific blood oxygen stores (total haemoglobin) fell during the study period. Simultaneously, the following behavioural indicators of diving ability increased: the proportion of time spent in the water, dive depth, dive duration, bottom time and maximum daily swimming velocity. In addition, the proportion of dives that were identified by cluster analyses as being U-shaped increased significantly with age. On the basis of the measured blood oxygen stores, less than 1 % of the recorded dives exceeded the calculated aerobic dive limit. Thus, development in blood oxygen stores or rates of oxygen consumption did not seem to restrain the rate of neonatal dive development in harbour seals. It appears that behavioural modifications (experience and learning) may be the primary rate-limiting factors for ontogeny of diving skills in neonates of this species.