Marine Biology (2002) 141: 581–589 DOI 10.1007/s00227-002-0843-4 J.-B. Charrassin Æ Y. Le Maho Æ C.-A. Bost Seasonal changes in the diving parameters of king penguins (Aptenodytes patagonicus) Received: 3 May 2001 / Accepted: 18 March 2002 / Published online: 5 July 2002 Ó Springer-Verlag 2002 Abstract Contrastingconditions at-sea are likely to af- and with dive depth, but they were longer in spring fect the foraging behaviour of seabirds. However, the (2.3 min for dives over the 100–210 m layer) and sum- effect of season on the dive parameters of penguins is mer than in autumn and winter (1.6–1.8 min). The div- poorly known. We report here on an extensive study of ingefficiency decreased with increasingdive depth and the divingbehaviour of kingpenguins( Aptenodytes was higher in autumn and winter (0.22–0.29) than in patagonicus) over the bird’s complete annual cycle at the summer and spring(0.15–0.18). The largeincrease Crozet Islands. Time-depth recorders were used to re- in bottom and dive duration from springto winter is in cord dive duration, bottom duration, post-dive interval, agreement with the seasonal drop in prey density, with ascent rate and descent rate in breedingadults during penguins spending more time searching for prey. In different seasons in 1995 and 1996. Seasons included contrast, the consistency of the vertical velocity during summer (n=6, incubation; n=6, chick brooding), au- contrasting conditions at-sea suggests that the transit tumn and winter (n=5 and n=3, respectively, chick at time to depth is an important component of the foraging the cre` che stage), and spring (n=4, birds at the post- behaviour (scanningof the water column) that is inde- moult stage). In all seasons dive duration increased with pendent of the prey availability. The time budget of the dive depth, but, for a given depth, dives were longer in penguins during diving in a fluctuating environment winter (6.8 min when averaged over the 100–210 m appears to vary primarily duringthe bottom phase of depth layer) than in spring(4.6 min) and summer the dives, with bottom duration increasingwith dimin- (4.4 min). The time spent at the bottom of the dives, ishingprey supplies, while post-dive intervals shorten in which probably represents a substantial part of the the same time. feedingtime, was much longerin winter (2.5 min per dive for dives over the 100–210 m layer) than during other seasons (1.0–1.4 min), i.e. there was a 2.5-fold Introduction augmentation for similar diving depths. Ascent and de- scent rates increased with increasingdive depth, but no In air-breathingdivers such as seabirds and pinnipeds, a difference in the relationships between rates of ascent dive typically consists of a descent phase to depth, a period and descent and dive depth was found amongseasons. spent at the bottom at maximum depth, and an ascent Furthermore, for all dive depths, ascent and descent phase of return to the surface (Schreer et al. 2001). This rates were independent of the bottom duration. In all basic pattern has been shown by numerous studies in seasons post-dive intervals increased with dive duration which the hydrostatic pressure encountered by the diver was recorded as a function of time by a miniaturised time- Communicated by S.A. Poulet, Roscoff depth recorder (TDR) carried by the animal (e.g. Kooy- man et al. 1992; Chappell et al. 1993; Wilson et al. 1996; J.-B. Charrassin (&) Æ Y. Le Maho Æ C.-A. Bost Kirkwood and Robertson 1997a; Georges et al. 2000; Centre d’Ecologie et Physiologie Energe´ tiques, Rodary et al. 2000). This large body of data has allowed Centre National de la Recherche Scientifique, major inter-specific comparisons of dive performance. 3 rue Becquerel, 67087 StrasbourgCedex, France Briefly, body size is the main source of variation between e-mail: [email protected] divingspecies, with largespecies divingdeeper and longer Tel.: +33-1-40793164 Fax: +33-1-40793163 than small species. Secondly, for most species investigated so far, dive duration and vertical velocity duringdiving Present address: J.-B. Charrassin strongly increase with increasing dive depth. These pat- Laboratoire d’Oce´ anographie Physique, Muse´ um National d’Histoire Naturelle, terns have been described in several reviews (e.g. Wilson 43 rue Cuvier, 75231 Paris Cedex 05, France 1995; Schreer et al. 2001). 582 However, most studies investigating dive patterns were post-dive interval, and vertical ascent and descent rates conducted duringsummer, which corresponds to the pe- across seasons. The results are discussed in terms of riod of the year when most species breed. At that time, the seasonal prey availability and behavioural adjustments. animals are readily accessible at the colony, their foraging trips are short, and they regularly return to the colony to feed their young. Consequently, the probability of re- Materials and methods coveringthe equipment is highestin summer. In contrast, few studies have attempted to compare intraspecifically Animals and instrumentation the divingbehaviour over different seasons. This is Field work was conducted in 1995 and 1996 at ‘‘La Grande probably related to logistic problems and to the limited Manchotie` re’’ colony, Possession Island, Crozet Archipelago memory size of instruments that does not allow coverage (46°25¢S; 51°45¢E). About 40,000 pairs of kingpenguins( Apteno- of the entire duration of the much longer winter trips. dytes patagonicus) breed in this colony, with the whole Crozet However, the marine environment shows strongseasonal Archipelago (1 million pairs) representing 50% of the world population (Guinet et al. 1995). The divingbehaviour of 21 birds changes in biological production (Foxton 1956; Clarke was monitored so that birds over the complete annual cycle of the 1988), which can have a profound impact on the feeding kingpenguinwere represented, as described in Charrassin and Bost ecology of predators. The winter season is characterised (2001). Birds studied in summer (1995) were either incubatingor by a drastic drop in the marine primary production. Pre- broodinga 1- to 3-week-old chick. Birds studied in autumn (1995) and in winter (1995–1996) were caringfor an emancipated chick at dators breedingon the Antarctic continent may respond the cre` che stage (i.e. older than 6 weeks). Birds studied in spring by a shift of their diet, e.g. from fish (summer) to krill (1996) were at the post-moult stage; they were unsuccessful (winter) in emperor penguins (Aptenodytes forsteri)orby breeders from 1995 that were randomly captured just after moult in long-distance migrations in Ade´ lie (Pygoscelis adeliae) the earliest cohort of moulting penguins. All foraging trips were and chinstrap penguins (Pygoscelis antarctica) (Davis performed by different individuals, except for three birds for which we studied the foraging activity at the incubating and brooding et al. 1996; Kirkwood and Robertson 1997b; Wilson et al. stages consecutively. TDRs deployed in summer, autumn and 1998). In the permanently open-ocean zone, zooplankton winter were Mk5 3.0 (95·38·15 mm, 70 g) (Wildlife Computers, (e.g. copepods) migrate to greater depth in winter, fol- USA), and those used at the post-moult stage were Mk5 3.3 lowed by some zooplankton consumers (e.g. mesopelagic (110·38·15 mm, 90 g). The TDRs recorded hydrostatic pressure with a 2 m depth resolution over a range of 0–500 m and had a fish) which, in turn, are potential prey of divingpredators 512 kb memory. The samplinginterval was 5 s in summer, and 10 s (Smith and Schnack-Schiel 1990; Koslov et al. 1991; duringthe autumn, winter and post-moultingperiods. Depth Ridoux 1994; Woehler 1995). Most species desert their measurements were made every second day in the winter cre` che breedingcolony in winter, and probably travel to more group to allow for complete coverage of long trips. To reduce the hydrodynamic drag(Bannasch et al. 1994), the TDRs were fitted to productive regions, but comprehensive behavioural data the lower back of the birds. Cable-ties were used to fix the TDRs to are missing. Inter-seasonal dive studies can elucidate the a small metal grid, which was glued to the feathers of the back with short-scale responses of divingpredators to these drasti- fast epoxy. Birds were flipper marked with coloured tape. After cally contrastingat-sea conditions. A few studies exist for equipment, the birds were released close to the edge of the colony. seals (e.g. Georges et al. 2000), but, with exception of a All birds were freed of their devices upon their return. Maximum care was taken to reduce the stress to the birds, e.g., by covering the study on gentoo penguins (Pygoscelis papua) at South birds’ eyes duringhandlingand by movingcarefully. Georgia (Williams et al. 1992b) and one on king penguins at Heard Island (Moore et al. 1999), virtually nothingis known about penguins. Analysis of divingbehaviour As part of a long-term study, we examined the for- A dive-per-dive analysis was conducted on depth data that were aging behaviour of the king penguin (Aptenodytes pat- corrected for surface drift (range: ±2 to 10 m) using custom-made agonicus) at the Crozet Islands over its annual cycle software (Jensen Software Systems, Laboe, Germany). Only dives (Bost et al. 1997; Charrassin et al. 1998, 1999; ‡4 m were analysed, because dives <4 m could not be reliably re- solved by the instruments. Maximum dive depth, dive duration, post- Charrassin and Bost 2001). The kingpenguinis an dive interval, time spent at the bottom and vertical dive velocities oceanic, deep diver that feeds on mesopelagic fish dis- were obtained. Post-dive intervals were calculated between consec- tributed at depths of 100–500 m.