No abstract

Penguins are major consumers in the marine environment. However, like many top predators, very little information exists on their foraging behaviour outside the breeding season. We investigated the foraging behaviour of the macaroni penguin Eudyptes chrysolophus continuously for 2 consecutive years, from the end of December 2001. This allowed us to investigate whether foraging behaviour varied between sexes, years or phases of the annual cycle. Male penguins tended to dive deeper and longer than female penguins, but at a lower frequency, probably as a result of their larger body size. There was little variation in foraging behaviour between the 2 years studied, although neither year included a notable period of low Antarctic krill abundance. Diving behaviour varied substantially within years and general linear models were used to investigate this variability. In summary, all penguins tended to dive deeper, longer and more efficiently during their winter migration than during the summer breeding season. The penguins dived predominantly during daylight hours at all times of the year, but appeared to be more constrained by daylight during the short winter days. Several diving variables including dive duration, dive rate and amount of time spent diving were significantly related to day length and these associations were stronger during winter than summer. The macaroni penguin shows flexibility in its foraging behaviour as it adapts to differing constraints and challenges during its annual cycle. KEY WORDS: Behavioural plasticity · Penguin · Southern Ocean · Diving behaviour · Eudyptes chrysolophus Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 296: [183][184][185][186][187][188][189][190][191][192][193][194][195][196] 2005 hence food demands are likely to be high (Green et al. 2002), but there is currently no information about the location, foraging habits or diet of macaroni penguins during this period.This paucity of information on year-round behaviour is not restricted to macaroni penguins. With the exception of some information on location (Weimerskirch & Wilson 2000, no other seabirds, or indeed any other marine predators, have had their foraging behaviour studied continuously throughout their annual (or biannual) cycle. However, several species have been studied at different times of year, or at the same time in years of differing environmental conditions, including king penguins Aptenodytes patagonicus (Charrassin & Bost 2001) and Antarctic fur seals Arctocephalus gazella . These studies frequently identified differences in foraging patterns at different times of the year. The changes are often related to differences in foraging location and therefore the underlying oceanography/topography (Charrassin & Bost 2001 and/or prey species (Kato et al. 2003). This flexibility in behaviour illustrates the importance of studying animals at all stages of their life history, in order to understand how they interact with their environment and how they might re...

1. The measurement of energy expenditures in free-ranging animals is essential if we are to understand fully the interaction between a species and its environment. This study examined the validity of heart rate (fH) and doubly labelled water (DLW) as measures of field metabolic rate (FMR) in California Sea Lions (Zalophus californianus). 2. Oxygen consumption and CO2 production were measured over 24 h by direct respirometry in six juvenile sea lions. The respirometer consisted of a hood over a flume in which the sea lions were exercised to various levels for 15 min periods throughout each experiment. The exercise regime produced a mean metabolic rate which was 2.3 times the predicted basal metabolic rate (BMR) with mean maxima of 6.27 times the predicted BMR. 3. Simultaneously with direct respirometry, mean CO2 production was estimated using DLW and 02 consumption was estimated using fH, which had previously been calibrated against 02 consumption. 4. The mean ? SD 02 consumptions from direct respirometry, fH and DLW were 11 80?240, 11.95?2.17 and 15 01?3 77ml min-' kg-' respectively. Paired Student's t-tests showed no significant difference between 02 consumption by direct respirometry and the estimates from DLW andfH. DLW measurements ranged from-10% to +86% of the direct respirometry measurements (mean +36.4%) and fH measurements ranged from-28% to +23% of the direct respirometry measurements (mean +2.7%). 5. The range of estimated metabolic rates fromfH was largely owing to individual differences in the slopes of the linear relationship betweenfH and 02 consumption. The range of metabolic rates from DLW could be partly attributed to the short duration of the experiments (24-25 h) but this was shown not to be the cause of the tendency to overestimate metabolic rate from DLW. It was concluded that both DLW and fH are valid methods for measuring FMR in California Sea Lions although it is possible that FMR could be overestimated when using DLW.

No abstract

regulate their body temperature within narrow margins to optimize their metabolic functions (Blaxter Biological Sciences,