Sex differences in Adélie penguin foraging strategies

Consistent sex differences in foraging trip duration, feeding locality and diet of breeding Adélie penguins (Pygoscelis adeliae) were demonstrated at two widely separated locations over several breeding seasons. Differences in foraging behaviour were most pronounced during the guard stage of chick rearing. Female penguins made on average longer foraging trips than males, ranged greater distances more frequently and consumed larger quantities of krill. In contrast, males made shorter journeys to closer foraging grounds during the guard period and fed more extensively on fish throughout chick rearing. Mean guard stage foraging trip durations over four seasons at Béchervaise Island, Eastern Antarctica and over two seasons at Edmonson Point, Ross Sea ranged between 31 and 73 h for females and 25 and 36 h for males. Ninety percent of males tracked from Béchervaise Island by satellite during the first 3 weeks post-hatch foraged within 20 km of the colony, while the majority (60%) of females travelled to the edge of the continental shelf (80–120 km from the colony) to feed during this period. Received: 10 December 1997 / Accepted: 10 April 1998     

Susceptibility to oxidative stress in Adélie and emperor penguin

The antioxidant defences in aerobic organisms represent the detoxification pathway against toxicity of reactive oxygen species (ROS). These highly reactive molecules are normally produced during the 4-electrons reduction of molecular oxygen to water coupled with oxidative phosphorylation, and during the activity of several enzymatic systems which produce ROS as intermediates. However, the endogenous generation of oxyradicals may be influenced by different environmental and biological factors, and the basal efficiency of antioxidant systems generally reflects the normal prooxidant pressure to which organisms are exposed. If the antioxidant capacity is exceeded (i.e. as a consequence of enhanced intracellular formation of ROS), a pathological condition, generally termed oxidative stress, may arise. In this preliminary work, susceptibility to oxidative stress has been compared in plasma of Adélie penguin (Pygoscelis adeliae), emperor penguin (Aptenodytes forsteri), south polar skua (Catharacta maccormicki) and snow petrel (Pagodroma nivea). Within the framework of the Italian Research Program in Antarctica, blood samples were collected during the austral summer 1998-1999 and the Total Oxyradical Scavenging Capacity (TOSC) analysed. The TOSC assay, measuring the capability of biological samples to neutralise different oxyradicals, has been recently standardised to provide a quantifiable value of biological resistance to toxicity of ROS. Penguins exhibited higher scavenging capacity towards peroxyl radicals than south polar skua and snow petrel. The greater resistance to toxicity of oxyradicals might suggest that penguins are naturally exposed to a higher basal prooxidant pressure in comparison to other analysed Antarctic birds.     

Holocene Adélie penguin diet in Victoria Land,Antarctica

Ornithogenic soils (N = 97) dated up to 7000 Before Present (bp) were sampled in 16 relict and modern breeding colonies of Adélie penguin along the Victoria Land coast (Ross Sea, Antarctica). Taxonomic identification of fish otoliths (N = 677) recovered in these soils allowed to identify the Antarctic silverfish as the most eaten prey (90.1%) throughout the investigated period. A morphometric analysis of the otoliths revealed that the Adélie penguin primarily selected prey averaging 67.23 ± 23 mm of standard length. Temporal distribution of Pleuragramma antarcticum showed a peak between 2,000 and 4,000 years bp, a period corresponding to the maximum spread of Adélie penguin in the Victoria Land. Possible explanations of the variations of the abundance of the fish prey in the diet are discussed in the context of the paleoclimatic events and as possible consequences of dietary shifts due to the temporal variation of prey availability in the Ross Sea ecosystem.     

Energy requirements of Adélie penguin (Pygoscelis adeliae) chicks

Summary The energy requirements of Adélie penguin (Pygoscelis adeliae) chicks were analysed with respect to body mass (W, 0.145–3.35 kg, n=36) and various forms of activity (lying, standing, minor activity, locomotion, walking on a treadmill). Direct respirometry was used to measure O₂ consumption ( ) and CO₂ production. Heart rate (HR, bpm) was recorded from the ECG obtained by both externally attached electrodes and implantable HR-transmitters. The parameters measured were not affected by hand-rearing of the chicks or by implanting transmitters. HR measured in the laboratory and in the field were comparable. Oxygen uptake ranged from in lying chicks to at maximal activity, RQ=0.76. Metabolic rate in small wild chicks (0.14–0.38 kg) was not affected by time of day, nor was their feeding frequency in the colony (Dec 20–21). Regressions of HR on were highly significant (p< 0.0001) in transmitter implanted chicks (n=4), and two relationships are proposed for the pooled data, one for minor activities ( ), and one for walking ( ). Oxygen consumption, mass of the chick (2–3 kg), and duration of walking (T, s) were related as , whereas mass-specific O₂ consumption was related to walking speed (S, m·s^-1) as .Abbreviations bpm beats per minute - D distance walked (m) - ECG electrocardiogram - HR heart rate (bpm) - ns number of steps - RQ respiratory quotient - S walking speed (m·s^-1) - T time walked (s) - W body mass (kg)     

Sea ice affects the population dynamics of Adélie penguins in Terre Adélie

Overall Adélie penguin population size in Pointe Géologie Archipelago increased between 1984 and 2003 at a rate of 1.77% per year, and averaged 33,726±5,867 pairs. As predicted by the optimum model proposed by Smith et al. (Bioscience 49:393–404, 1999). Adélie penguin population size increased when sea ice extent and concentration (SIE and SIC) decreased six years earlier, indicating that the conditions around reproduction or first years at sea, were determinant. The breeding success averaged 85.2±35.45% and was not related to environmental variables. Adult survival probability varied between years from 0.64 to 0.82. Southern oscillation index (SOI) had a strong negative effect on adult annual survival. Adult survival of Adélie penguins increased during warmer events, especially during winter and spring at the beginning of reproduction. Therefore, we speculate that the rapid decreases in 1988–1991 and 1996 of the breeding population size were related to a decrease in adult mortality. However, adult survival varied little, and could not explain the strong increasing population trend. The sea ice conditions during breeding or during the first year at sea appeared determinant and influenced the population dynamics through cohort effects, probably related to the availability of productive feeding habitats.     

An albinistic Adélie penguin breeding at Amundsen Bay, Antarctica

An albinistic penguin of Pygoscelis adeliae, found in the colony located in the southwestern part of the Mt. Riiser-Larsen area, Amundsen Bay, Enderby Land, was incubating a single egg. Accepted: 18 September 1999     

Satellite tracking of Adélie penguins

Summary Female Adélie penguins (Pygoscelis adeliae) that take too long on their first post-laying foraging trip are a major cause of breeding failure, but in the ice-filled waters of Antarctica, determining where they go and why they are away so long has proved difficult. Here we describe the first successful attempt to track penguins at sea using satellite telemetry. Four females foraged in different locations, dispelling the notion of a common feeding ground. They moved up to 272 km from the rookery and covered from 551 to 1,121 km on their trips, swimming at minimum average speeds around 1.2 m/s. The birds were most likely to be in the water between 0630 and 1430 when light intensity, important for a visual predator, was greatest. Carrying the transmitters reduced rates of fat deposition (weight gain), increasing the duration of foraging trips of females, and suggested that they may forage until their fat depots reach a minimum threshold level. This has two implications: (i) durations of these postlaying foraging trips could potentially be used as an indicator of krill abundance (Euphausia sp), the almost exclusive food of Adélie penguins during this period, and (ii) any reduction in krill stocks caused by harvesting could increase foraging trip durations with a concomitant increase mi breeding failures.     

Haplotyping cryptic Adélie penguin taxa using low-cost,high-resolution melt curves

Distinguishing morphologically cryptic taxa, by definition, requires genetic data such as DNA sequences. However, DNA sequences may not be obtained easily for taxa from remote sites. Here we provide the details of a high-resolution melt-curve-based method using taxon-specific primers that can distinguish two taxa of Adélie penguins, and that will be usable in Antarctica when combined with some of the newly developed field-deployable thermal cyclers. We suggest that the wider adoption of field-deployable polymerase-chain-reaction-based techniques will enable faster assignation of haplotype to individuals in situ, and so allow the targeting of observations and sample collection to specimens relevant to the research question. Targeting individuals will also reduce the need to repeatedly handle animals and reduce the time and travel required to complete field work.     

Synchronous diving behavior of Adélie penguins

Synchronizing behavior with other conspecifics has been suggested as serving a function of increased foraging efficiency. However, the potential costs associated with synchronization of behavior have rarely been studied. Adélie penguins Pygoscelis adeliae sometimes dive synchronously in small open waters surrounded by fast sea ice. We examined the diving behavior of three couples and one trio, which were observed to dive synchronously among groups of 12–47 birds for 1.7–4.5 h duration, with time-depth recorders. Timing of diving and surfacing differed slightly between individuals, and one bird tended to initiate diving earlier than the other. Although the duration of the dives differed only slightly between these birds, the maximum depth of the dives differed to a large extent, with one member tending to dive consistently deeper than the other bird in two out of the four cases. Vertical distances between tagged birds in the undulatory phases of the dives (presumed feeding time) were greater than those in the descent and ascent phases, suggesting independent foraging by group members. Duration of the undulatory phase of the dives tended to be shorter in deeper-diving individuals than the others in the synchronously diving group, suggesting a potential cost of reduced feeding time to synchronize diving and surfacing with other birds. A digital video image relating to the article is available at .     

Adélie penguin survival: age structure,temporal variability and environmental influences

The driving factors of survival, a key demographic process, have been particularly challenging to study, especially for winter migratory species such as the Adélie penguin (Pygoscelis adeliae). While winter environmental conditions clearly influence Antarctic seabird survival, it has been unclear to which environmental features they are most likely to respond. Here, we examine the influence of environmental fluctuations, broad climatic conditions and the success of the breeding season prior to winter on annual survival of an Adélie penguin population using mark–recapture models based on penguin tag and resight data over a 16-year period. This analysis required an extension to the basic Cormack–Jolly–Seber model by incorporating age structure in recapture and survival sub-models. By including model covariates, we show that survival of older penguins is primarily related to the amount and concentration of ice present in their winter foraging grounds. In contrast, fledgling and yearling survival depended on other factors in addition to the physical marine environment and outcomes of the previous breeding season, but we were unable to determine what these were. The relationship between sea-ice and survival differed with penguin age: extensive ice during the return journey to breeding colonies was detrimental to survival for the younger penguins, whereas either too little or too much ice (between 15 and 80% cover) in the winter foraging grounds was detrimental for adults. Our results demonstrate that predictions of Adélie penguin survival can be improved by taking into account penguin age, prior breeding conditions and environmental features.     

Ontogeny of hepatic microsomal 3-hydroxylation of quinine in Adélie Penguins

Ontogeny of hepatic cytochrome P450 (CYP) content and of quinine 3-hydroxylation, a biomarker of human CYP3A activity, was investigated in Adélie Penguins (Pygoscelis adeliae) by comparing liver microsomes from chicks aged 13-28 days (n=10) with those from adults. The total CYP content in chick microsomes was significantly lower than in adults and correlated with the age of the chicks (r=0.894, P<0.001). Kinetic parameters (mean+/-S.D.) for quinine 3-hydroxylation in chick microsomes were lower than the corresponding values in adult penguins (Km, 122+/-27 vs. 160+/-73 microM; Vmax, 119+/-35 vs. 160+/-72 pmol/min/mg protein) but the differences were not significant, and neither Km nor Vmax correlated with age of the chicks. The pattern of inhibition of quinine 3-hydroxylation by specific human CYP inhibitors suggests that the CYP enzyme mediating quinine 3-hydroxylation in penguin chicks is similar to human CYP3A, but is a different isoform from that in adult penguins. The results imply that Adélie Penguin chicks may have a different susceptibility to environmental pollutants from adult penguins.     

Human-induced behaviour in Adélie penguins Pygoscelis adeliae

Summary Adélie penguins Pygoscelis adeliae appear to be little perturbed by man. We examined the incidence of nest desertion and duration of foraging trip in Adélie penguins when manipulated and fitted with devices of differing sizes. Birds with ca. 1 cm clipped from their tail feathers stayed at sea 50% longer than unmarked controls. The length of foraging trip and incidence of nest desertion increased with increasing device volume. Penguins fitted with devices did not reduce foraging trip length to that of unpackaged birds for at least 19 days. The susceptibility of Adélie penguins to disturbance should be carefully considered when activity patterns are being studied.     

Factors affecting fledging weight of Adélie penguin (Pygoscelis adeliae) chicks: a modeling study

An individual-based model is developed to examine mechanisms that potentially underlie the observed constancy in fledging weight (2.8-3.2 kg) of Adélie (Pygoscelis adeliae) penguin chicks, in spite of large variability in the abundance of Antarctic krill (Euphausia superba), the primary food source. The model describes the energetic requirements of the chick, with growth resulting from the difference between assimilated energy and respiration. Parameterizations of these metabolic processes are based upon experimental and field observations. Ingestion of Antarctic krill by the chick is dependent on the frequency of food delivery to the chick by the adults, which is based on measured foraging times. The mass, size, and size frequency distribution of Antarctic krill fed to the chick are specified using empirical data. The energy content of the Antarctic krill provided to the chick is taken to be constant or allowed to vary with size. The simulations show that food availability is most critical in the latter portion of chick development, when growth rates and food demands are high. Low food availability during this time must be compensated by either feeding chicks with larger krill of higher caloric value or by increased assimilation efficiency. Periods when small krill with lower caloric value dominate require more frequent feeding of the chicks in order to attain their observed fledging weight. Thus, although the total food energy given to the chick is the main factor determining chick growth, the distribution of food availability relative to chick size (i.e., different net growth rates) and food quality are also factors influencing the fledging weight of penguin chicks. The simulations provide insight into the compensating effects of food delivery, food quality, and metabolic processes that allow Adélie penguin chicks to reach their observed fledging weight in spite of considerable environmental variability in food supply.     

Changes in Adélie penguin breeding populations in Lützow-Holm Bay, Antarctica, in relation to sea-ice conditions

The Adélie penguin, Pygoscelis adeliae, an important component of the Antarctic marine ecosystem, is closely associated with sea ice. Using data collected by Japanese Antarctic Research Expeditions since the 1960s, we examined trends in breeding populations of this species around Lützow-Holm Bay. Ten colonies ranging in size from 10 to 2,500 individuals were counted along the Soya Coast. Populations fluctuated synchronously, and overall increased at most colonies, except for two: one located deep inside the bay and another where human disturbance was substantial. Populations tended to increase during, or after, periods of sparse sea ice in summer, a condition that occurred once every decade. An increase in population size also occurred 5 years after a winter of extensive sea ice and after a winter of especially reduced sea ice.     

Gene flow on the ice: genetic differentiation among Adélie penguin colonies around Antarctica

Each summer Adélie penguins breed in large disjunct colonies on ice-free areas around the Antarctic continent. Comprising > 10 million birds, this species represents a dominant feature of the Antarctic ecosystem. The patchy distribution within a large geographical range, natal philopatry and a probable history of refugia, suggest that this species is likely to exhibit significant genetic differentiation within and among colonies. We present data from seven microsatellite DNA loci for 442 individuals from 13 locations around the Antarctic continent. With the exception of one locus, there was no significant genic or genotypic heterogeneity across populations. Pairwise FST values were low with no value > 0.02. When all colonies were compared in a single analysis, the overall FST value was 0.0007. Moreover, assignment tests were relatively ineffective at correctly placing individuals into their respective collection sites. These data reveal a lack of genetic differentiation between Adélie penguin colonies around the Antarctic continent, despite substantial levels of genetic variation. We consider this homogeneity in terms of the dispersal of individuals among colonies and the size of breeding groups and discuss our results in terms of the glacial history of Antarctica.     

New methods and technologies for regional-scale abundance estimation of land-breeding marine animals: application to Adélie penguin populations in East Antarctica

Land-breeding marine animals such as penguins, flying seabirds and pinnipeds are important components of marine ecosystems, and their abundance has been used extensively as an indication of ecosystem status and change. Until recently, many efforts to measure and monitor abundance of these species’ groups have focussed on smaller populations and spatial scales, and efforts to account for perception bias and availability bias have been variable and often ad hoc. We describe a suite of new methods, technologies and estimation procedures for cost-effective, large-scale abundance estimation within a general estimation framework and illustrate their application on large Adélie penguin populations in two regions of East Antarctica. The methods include photographic sample counts, automated cameras for collecting availability data, and bootstrap estimation to adjust counts for the sampling fraction, perception bias, and availability bias, and are applicable for a range of land-breeding marine species. The methods will improve our ability to obtain population data over large spatial and population scales within tight logistic, environmental and time constraints. This first application of the methods has given new insights into the biases and uncertainties in abundance estimation for penguins and other land-breeding marine species. We provide guidelines for applying the methods in future surveys.     

Fluctuations in Adélie penguin prey size in the mid to late Holocene, northern Marguerite Bay, Antarctic Peninsula

We investigated temporal changes in Adélie penguin prey size in northern Marguerite Bay, Antarctic Peninsula, through excavations of three abandoned and one active colony at Lagoon (67°35'S, 68°16'W) and Ginger Islands (67°45'S, 68°41'W), respectively, in austral summer 1999/2000. Radiocarbon dates on penguin bones and eggshell fragments collected at each site indicate that Lagoon Island was first occupied after 6000 BP and Ginger Island near 2275 BP. Identifiable non-krill prey remains (otoliths and squid beaks) were recovered from ornithogenic soils at all sites, with Antarctic silverfish (Pleuragramma antarcticum) and squid (Psychroteuthis glacialis) being the most abundant species represented in the deposits. Estimated mean standard lengths and mantle lengths of these two prey taxa, based on regressions with otolith and beak measurements respectively, indicate that Adélie penguins primarily select these prey within a mean size range of 95-117 mm. Prey size also varied significantly across seven occupation periods from 6000 BP to the present, but did not correlate with climate change.     

Strategic allocation of ejaculates by male Adélie penguins

Sperm competition theory suggests that males should strategically allocate sperm to those females that will bring them the best possible genetic returns. Although males of a number of species of insects and fishes have been shown to allocate sperm strategically, we provide, to our knowledge, the first evidence that an avian species is also capable of allocating ejaculates. Male Adélie penguins (Pygoscelis adeliae) are more likely to transfer sperm during extra-pair copulations (EPCs) than during pair copulations. We investigated the question of how males allocate ejaculates within the constraints of limited sperm availability and found (i) that males that engaged in EPC attempts ejaculated less often when copulating with their social partner than males that made no EPC attempts, and (ii) that there was no difference between males that were involved in failed EPC attempts and those that were involved in successful EPCs in the proportion of copulations that resulted in sperm transfer. These results indicate that males achieve strategic allocation of sperm within the constraints of limited sperm availability by withholding ejaculates from their social partners.     

Should I stay or should I go? Hormonal control of nest abandonment in a long-lived bird,the Adélie penguin

According to life-history theory, long-lived birds should favor their survival over the current reproductive attempt, when breeding becomes too costly. In seabirds, incubation is often associated with spontaneous long-term fasting. Below a threshold in body reserves, hormonal and metabolic shift characteristics of a switch from lipid to protein utilization (phase III, PIII) occur. These metabolic changes are paralleled by nest abandonment and stimulation of refeeding behavior. Parental behavior is then under control of two hormones with opposite effects: corticosterone (CORT) and prolactin which stimulate foraging and incubation behavior, respectively.The aim of this study was to determine the respective role of these two hormones in nest abandonment by Adélie penguins. To this end, plasma hormone levels were measured before egg-laying and at departure from the colony (i.e. when birds were relieved by their partner or abandoned their nest), and related to nutritional state and incubation success.We found that males abandoning their nest in PIII presented high CORT levels and low prolactin levels. Interestingly, males which presented high plasma levels of prolactin in PIII did not abandon. We show that although CORT is the first hormone to be affected by prolonged energy constraints, the combined effects of high CORT and low prolactin levels are necessary for parents to favor self-maintenance and abandon the nest. We provide insights into time-course changes of the endocrine profile as PIII proceeds and report that reaching proteolytic late fasting is not sufficient to induce nest abandonment in a long-lived bird.