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C A Bost – One of the best experts on this subject based on the ideXlab platform.

  • Massive decline of the world’s largest king penguin colony at Ile aux Cochons, Crozet
    Antarctic Science, 2018
    Co-Authors: Henri Weimerskirch, Fabrice Le Bouard, Peter G. Ryan, C A Bost

    Abstract:

    King penguins (Aptenodytes patagonicus Miller) are major consumers in the Southern Ocean. The colony at Ile aux Cochons, Iles Crozet, in the southern Indian Ocean was known in the 1980s as the largest king penguin colony and the second largest penguin colony in the world. However, there have not been any recent estimates of this colony. Aerial photographs taken from a helicopter, and satellite images were used to report on changes in the colony and population sizes over the past 50 years. The colony has declined by 88% over the past 35 years, from c. 500 000 pairs to 60 000 pairs. The possible causes of this decline were explored but no plausible explanation for such an unprecedented decrease in penguin populations was found. The study highlights the use of satellite imagery as a non-invasive technique for population monitoring, and stresses the need for further research on the causes of this alarming trend in this colony.

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  • Seasonal changes in the diving parameters of king penguins (Aptenodytes patagonicus)
    Marine Biology, 2002
    Co-Authors: J. B. Charrassin, Y. Le Maho, C A Bost

    Abstract:

    Contrasting conditions at-sea are likely to affect the foraging behaviour of seabirds. However, the effect of season on the dive parameters of penguins is poorly known. We report here on an extensive study of the diving behaviour of king penguins (Aptenodytes patagonicus) over the bird’s complete annual cycle at the Crozet Islands. Time-depth recorders were used to record dive duration, bottom duration, post-dive interval, ascent rate and descent rate in breeding adults during different seasons in 1995 and 1996. Seasons included summer (n=6, incubation; n=6, chick brooding), autumn and winter (n=5 and n=3, respectively, chick at the creche stage), and spring (n=4, birds at the post-moult stage). In all seasons dive duration increased with dive depth, but, for a given depth, dives were longer in winter (6.8 min when averaged over the 100–210 m depth layer) than in spring (4.6 min) and summer (4.4 min). The time spent at the bottom of the dives, which probably represents a substantial part of the feeding time, was much longer in 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 augmentation for similar diving depths. Ascent and descent rates increased with increasing dive depth, but no difference in the relationships between rates of ascent and descent and dive depth was found among seasons. Furthermore, for all dive depths, ascent and descent rates were independent of the bottom duration. In all seasons post-dive intervals increased with dive duration and with dive depth, but they were longer in spring (2.3 min for dives over the 100–210 m layer) and summer than in autumn and winter (1.6–1.8 min). The diving efficiency decreased with increasing dive depth and was higher in autumn and winter (0.22–0.29) than in summer and spring (0.15–0.18). The large increase in bottom and dive duration from spring to winter is in agreement with the seasonal drop in prey density, with penguins spending more time searching for prey. In contrast, the consistency of the vertical velocity during contrasting conditions at-sea suggests that the transit time to depth is an important component of the foraging behaviour (scanning of the water column) that is independent of the prey availability. The time budget of the penguins during diving in a fluctuating environment appears to vary primarily during the bottom phase of the dives, with bottom duration increasing with diminishing prey supplies, while post-dive intervals shorten in the same time.

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  • benthic diving in male emperor penguins Aptenodytes forsteri foraging in winter
    Marine Ecology Progress Series, 2000
    Co-Authors: D Rodary, Le Y Maho, W Bonneau, C A Bost

    Abstract:

    We studied the foraging areas and diving depths of male emperor penguins Apten- odytes forsteri raising chicks at Pointe Geologie, Adelie Land, in relation to bathymetry and sea-ice conditions during the first foraging trip after incubation in August 1996 and 1997. Combining satel- lite-tracking and dive-recording devices on the same penguins allowed individual dives to be localised and related to water depth. The penguins mostly dived in zones less than 300 m deep, where they performed 50% of their dives and spent 54% of their bottom time near the sea floor, on average. Analyses including bathymetry and sea-ice cover for the 2 years suggest that after leaving the colony the penguins targeted the nearest available, fast-ice free shallow shelf waters (<300 m). Once in these areas, the penguins foraged by diving near the sea floor during most of the remaining part of their foraging trip. Day-by-day analysis showed that during this central part of the foraging trip, 68% of the dives ended near the sea floor. The most likely function of these dives appeared to be feeding on benthic or bentho-pelagic prey. Benthic dives were rare during the first and last days of trips, when penguins were apparently in transit. Benthic-feeding is interpreted as a strategy towards predictable prey during a critical stage of the breeding cycle. Shallow areas of the Antarctic conti- nental shelf may be important for some emperor penguin colonies around Antarctica. The importance of the benthic strata for this top predator of the Antarctic shelf ecosystem gives new insights on the trophic networks in the pack-ice during the Antarctic winter.

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Le Y Maho – One of the best experts on this subject based on the ideXlab platform.

  • heart rate and energetics of free ranging king penguins Aptenodytes patagonicus
    The Journal of Experimental Biology, 2004
    Co-Authors: G Froget, Andreas Fahlman, A. J. Woakes, Le Y Maho, P J Butler, Gregoire Kuntz, Yves Handrich

    Abstract:

    The main objective of this study was to determine heart rate ( f h) and the energetic costs of specific behaviours of king penguins while ashore and while foraging at sea during their breeding period. In particular, an estimate was made of the energetic cost of diving in order to determine the proportion of dives that may exceed the calculated aerobic dive limit (cADL; estimated usable O2 stores/estimated rate of oxygen consumption during diving).

    An implanted data logger enabled f h and diving behaviour to be monitored from 10 free-ranging king penguins during their breeding period. Using previously determined calibration equations, it was possible to estimate rate of oxygen consumption ( V O2) when the birds were ashore and during various phases of their foraging trips. Diving behaviour showed a clear diurnal pattern, with a mixture of deep (>40 m), long (>3 min) and shallow (<40 m), short (<3 min) dives from dawn to dusk and shallow, short dives at night. Heart rate during dive bouts and dive cycles (dive + post-dive interval) was 42% greater than that when the birds were ashore. During diving, f h was similar to the `ashore' value (87±4 beats min–1), but it did decline to 76% of the value recorded from king penguins resting in water. During the first hour after a diving bout, f h was significantly higher than the average value during diving (101±4 beats min–1) and for the remainder of the dive bout. Rates of oxygen consumption estimated from these (and other) values of f h indicate that when at sea, metabolic rate (MR) was 83% greater than that when the birds were ashore [3.15 W kg–1 (–0.71, +0.93), where the values in parentheses are the computed standard errors of the estimate], while during diving bouts and dive cycles, it was 73% greater than the `ashore' value. Although estimated MR during the total period between dive bouts was not significantly different from that during dive bouts [5.44 W kg–1 (–0.30, +0.32)], MR during the first hour following a dive bout was 52% greater than that during a diving bout. It is suggested that this large increase following diving (foraging) activity is, at least in part, the result of rewarming the body, which occurs at the end of a diving bout. From the measured behaviour and estimated values of V O2, it was evident that approximately 35% of the dives were in excess of the cADL. Even if V O2 during diving was assumed to be the same as when the birds were resting on water, approximately 20% of dives would exceed the cADL. As V O2 during diving is, in fact, that estimated for a complete dive cycle, it is quite feasible that V O2 during diving itself is less than that measured for birds resting in water. It is suggested that the regional hypothermia that has been recorded in this species during diving bouts may be at least a contributing factor to such hypometabolism.

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  • benthic diving in male emperor penguins Aptenodytes forsteri foraging in winter
    Marine Ecology Progress Series, 2000
    Co-Authors: D Rodary, Le Y Maho, W Bonneau, C A Bost

    Abstract:

    We studied the foraging areas and diving depths of male emperor penguins Apten- odytes forsteri raising chicks at Pointe Geologie, Adelie Land, in relation to bathymetry and sea-ice conditions during the first foraging trip after incubation in August 1996 and 1997. Combining satel- lite-tracking and dive-recording devices on the same penguins allowed individual dives to be localised and related to water depth. The penguins mostly dived in zones less than 300 m deep, where they performed 50% of their dives and spent 54% of their bottom time near the sea floor, on average. Analyses including bathymetry and sea-ice cover for the 2 years suggest that after leaving the colony the penguins targeted the nearest available, fast-ice free shallow shelf waters (<300 m). Once in these areas, the penguins foraged by diving near the sea floor during most of the remaining part of their foraging trip. Day-by-day analysis showed that during this central part of the foraging trip, 68% of the dives ended near the sea floor. The most likely function of these dives appeared to be feeding on benthic or bentho-pelagic prey. Benthic dives were rare during the first and last days of trips, when penguins were apparently in transit. Benthic-feeding is interpreted as a strategy towards predictable prey during a critical stage of the breeding cycle. Shallow areas of the Antarctic conti- nental shelf may be important for some emperor penguin colonies around Antarctica. The importance of the benthic strata for this top predator of the Antarctic shelf ecosystem gives new insights on the trophic networks in the pack-ice during the Antarctic winter.

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  • foraging strategies of incubating and brooding king penguins Aptenodytes patagonicus
    Oecologia, 1998
    Co-Authors: J. B. Charrassin, Klemens Pütz, J. Lage, T. Dahier, C A Bost, T Zorn, Le Y Maho

    Abstract:

    For oceanic birds like king penguins, a major constraint is the separation of foraging areas from the breeding colony, largely because swimming increases foraging costs. However, the relationship between foraging strategy and breeding stage has been poorly investigated. Using time-depth recorders, we studied the diving behaviour of two groups of king penguins that were either incubating or brooding chicks at Crozet Islands (Southern Indian Ocean) at the same period of the year. Although birds with chicks had the highest predicted energy demand, they made foraging trips half as long as incubating birds (6 vs. 14 days) and modified their time and depth utilisation. Birds with chicks dived deeper during daylight (mean maximum depth of 280 m vs. 205 m for those incubating). At night, birds with chicks spent twice as much time diving as those incubating, but birds at both stages never dived beyond 30 m. Movements to greater depths by brooding birds are consistent with the vertical distribution of myctophid fish which are the main prey. As chick provisioning limits trip duration, it is suggested that it is more efficient for parents to change their diving patterns rather than to restrict their foraging range.

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Yves Cherel – One of the best experts on this subject based on the ideXlab platform.

  • Food of emperor penguins (Aptenodytes forsteri ) in the western Ross Sea, Antarctica
    Marine Biology, 1998
    Co-Authors: Yves Cherel, Gerald L. Kooyman

    Abstract:

    The diet of the emperor penguin Aptenodytes forsteri in the western Ross Sea during spring was investigated by analysis of stomach contents sampled at three different localities. At Cape Washington, emperor penguins feeding chicks consistently preyed on fishes (89 to 95% by mass) and crustaceans (5 to 11%) over the four spring seasons examined. By far the commonest prey was the Antarctic silverfish Pleuragramma antarcticum (89% of the fish prey); the remainder of fish prey were mainly unidentified juveniles of different species of channichthyid fishes. Three species dominated the crustacean part of the diet, i.e. the gammarid amphipods Abyssorchomene rossi/plebs (30% of the crustacean prey) and Eusirus microps (22%), together with the euphausiid Euphausia crystallorophias (24%). At Coulman Island and Cape Roget, fishes, mainly P. antarcticum, formed the bulk of the food (88 and 93% by mass, respectively), crustaceans were minor prey (2.5 and 0.4%), and the squid Psychroteuthis glacialis accounted for a small but significant part of the food (3.5 and 0.8%). This study emphasizes the importance of the small, shoaling pelagic fish Pleuragramma antarcticum as a key link between zooplankton and top predators, including seabirds, in the food web and marine ecosystem of the Ross Sea.

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  • energy and protein requirements for molt in the king penguin Aptenodytes patagonicus
    American Journal of Physiology-regulatory Integrative and Comparative Physiology, 1994
    Co-Authors: Yves Cherel, J. B. Charrassin, Etienne Challet

    Abstract:

    Adult king penguins annually fast ashore for 1 mo for molting. By the end of molt, they have lost 44% of their prefasting body mass. About 18% of new feather synthesis occurs at sea, thus reducing both nutrient requirement and fasting duration. Plumage synthesis continues during the first 3 wk of fasting. Loss of old feathers occurs between day 12 and day 21 of the molt, and it is associated with a peak in daily body mass loss. The dry mass of epidermal structure synthesized during molt is 395 g. Body composition analysis indicates that fat oxidation accounts for 85% of total energy expenditure. The proportion for protein is 15%, a value twofold higher than during the breeding (nonmolting) fast. The mean energy expenditure is also 21% higher during the molting fast (3.04 W/kg). Compared with other birds, the energetic cost of feather synthesis is the lowest in king penguins (85 kJ/g) and consequently the energetic efficiency is the highest (25%). Changes in tissue composition during molt show that integument is the main lipid source (72% of the lipid loss) and thus the main source of energy (61% of the total energy expenditure). The integument and the pectoral muscles play a major role in molting protein metabolism, providing 20 and 57%, respectively, of the total protein needs for feather synthesis and/or energy expenditure. This result emphasizes the role of integument as a protein source, because the large premolting muscle hypertrophy is not sufficient to account for the totality of the protein cost of molt.

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  • Comparison of Body Reserve Buildup in Prefasting Chicks and Adults of King Penguins (Aptenodytes patagonicus)
    Physiological Zoology, 1993
    Co-Authors: Yves Cherel, Jean-benoît Charrassin, Yves Handrich

    Abstract:

    Like other penguin species, adult king penguins (Aptenodytes patagonicus) fast several weeks when they molt and at the beginning of their breeding cycle. Moreover, chicks of this species can withstand up to 5 mo of food deprivation during the austral winter. To assess possible variation in the prefasting amounts of nutrient reserves, we determined body composition (water, protein, total lipid, and ash contents) of adults and chicks of king penguins at the beginning of their long-term fasts. Accumulation of subcutaneous fat stores anticipates each of these periods and appears to be an obligatory prerequisite to fasting However, prewinter chicks contained 1 kg more fat and, consequently, had a higher adiposity (34%) than premolting chicks (22%) and prebreeding adults (18%), indicating that the higher the fat stores, the higher the fast resistance. Prewinter chicks also possess a 19% lower lean body mass (6 61 vs. 8.12 kg in premolting chicks), that is, a low amount of metabolically active tissues, thus mini…

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