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Seabirds breeding on the Antarctic continent must cope with extreme changes in sea ice cover and day length throughout the year. AdA©lie penguins are expected to adjust their migratory movements and diving activity to seasonal changes in foraging conditions, but their winter diving activities have not been examined previously. Here, we tracked 18 and 5 AdA©lie penguins by using geolocators with and without depth sensors, from a colony in East Antarctica over 2 winter seasons. After breeding, all but one penguin migrated westward from March to April, then moved northward from May to August as the sea ice edge extended to the north, then moved southeastward, returning towards the breeding colony. Migratory movements followed sea ice movements and the seasonal extension in this region, which is influenced by the west-flowing Antarctic Slope Current and wind. Penguins dived deeper during winter, reaching a maximum depth of 129 m. The birds dived mostly between civil dawn and dusk, and tended to stay on ice overnight. Diving effort (total time spent underwater per day) did not decline with sea ice concentrations, suggesting that penguins found open water to dive even with >90% sea ice cover. Diving effort was lowest around the winter solstice, but was relatively high before and after the annual moult, and also before the start of breeding when birds presumably needed to accumulate body reserves. Our results highlight how the migratory movement and winter diving activity of Adelie penguins are closely associated with the seasonal polar environment.

There is growing evidence that microplastic pollution (Pygoscelis papua from the Antarctic region (Bird Island, South Georgia and Signy Island, South Orkney Islands) and hence assess the potential for microplastic transfer through Antarctic marine food webs. To achieve this, the presence of microplastics in scats (as a proof of ingestion) was investigated to assess the viability of a non-invasive approach for microplastic analyses in Antarctic penguins. A total of 80 penguin scats were collected and any microplastics they contained were extracted. A total of 20% of penguin scats from both islands contained microplastics, consisting mainly of fibers and fragments with different sizes and polymer composition (mean abundance of microplastics: 0.23 ± 0.53 items individual−1 scat, comprising seven different polymers), which were lower values than those found for seabirds in other regions worldwide. No significant differences in microplastic numbers in penguin scats between the two regions were detected. These data highlight the need for further assessment of the levels of microplastics in this sensitive region of the planet, specifically studies on temporal trends and potential effects on penguins and other organisms in the Antarctic marine food web.

When successive stages of an organism's life-history overlap, conflicts and trade-offs can emerge due to competition among physiological pathways. For example, long periods of sustained locomotion in migrating birds are supported by the androgenic up-regulation of aerobic factors, such as new red blood cell production and hematocrit. However, towards the end of migration, many female birds begin up-regulating 17s-estradiol (E2) to support vitellogenesis and egg production, but E2 secretion is known to have suppressive effects on red blood cell production (anti-erythropoiesis). We explored potential trade-offs between factors related to aerobic performance (hematocrit, reticulocyte index) and the expression of factors related to E2-mediated vitellogenesis (i.e. yolk precursor production) in female macaroni penguins (Eudyptes chrysolophus), a species in which the physiologies controlling egg production and migratory activity run simultaneously (e.g. females experience a migratory conflict). We collected blood samples from penguins immediately upon their return to the colony, prior to egg laying. Hematocrit was elevated when the penguins returned to the colony (50.05% ± 3.40 SD), which is similar to pre-laying values observed in other migratory bird species. Furthermore, mean reticulocyte levels were elevated (34.87% ± 2.34), which is the highest level yet recorded in birds. Similarly, both plasma vitellogenin and yolk-targeted very low density lipoprotein levels were upregulated (2.30 ± 0.06 μg Zn ml−1, and 9.70 ± 0.19 mmol l−1, respectively), indicating that penguins were reproductively active and producing eggs during migration and upon arrival on land. As predicted, a negative relationship between hematocrit and plasma vitellogenin was found, but we found no evidence to suggest that birds were experiencing reproductive anemia. Alternatively, we attribute the negative relationship to a hemodilution effect of yolk precursor secretion into circulation. It appears that female macaroni penguins are able to preserve hematocrit levels and new red blood cell production when migratory activity overlaps with reproductive processes.

International audience; Penguins face a wide range of threats. Most observed population changes havebeen negative and have happened over the last 60 years. Today, populations of 11penguin species are decreasing. Here we present a review that synthesizes detailsof threats faced by the world’s 18 species of penguins. We discuss alterations totheir environment at both breeding sites on land and at sea where they forage. Themajor drivers of change appear to be climate, and food web alterations by marinefisheries. In addition, we also consider other critical and/or emerging threats, namelyhuman disturbance near nesting sites, pollution due to oil, plastics and chemicals suchas mercury and persistent organic compounds. Finally, we assess the importance ofemerging pathogens and diseases on the health of penguins. We suggest that in the context of climate change, habitat degradation, introduced exotic species andresource competition with fisheries, successful conservation outcomes will require newand unprecedented levels of science and advocacy. Successful conservation storiesof penguin species across their geographical range have occurred where there hasbeen concerted effort across local, national and international boundaries to implementeffective conservation planning.

International audience; There is a growing search for less invasive methods while studying the diet of Antarctic animals in the wild. Therefore,we compared the diet of gentoo penguins from stomach contents (i.e. through visual identification of prey remains) andscats (i.e. faeces), and further compared prey DNA assay in fresh and old scats. Prey remains identified visually in stomachcontents and scats were broadly comparable: the crustaceans and fish were the most important components, with Themistogaudichaudii clearly being the most frequent and numerous prey species in both sampling methods. By mass, differencesin species frequency were observed in stomach contents (Parachaenichthys georgianus) and scats (Champsocephalus gunnari),with the former fish species absent in scats. Differences were detected in the most frequent prey (T. gaudichaudiiand Euphausia superba) and in various fish species, most with bigger sizes in scats. Allometric equations to estimate mostcrustacean’s sizes (i.e. relationships between carapace and mass/total length) are needed. For DNA studies, when comparingDNA from fresh and old scats, both provided similar results that, in general, were also similar to the visual analysis. In orderto use penguin scats (along with the use of DNA analyses) for monitoring purposes, allometric equations to estimate massand size of prey (most crustaceans) and better designed species-specific primers are needed for targeting key prey species(e.g. Euphausia superba, T. gaudichaudii). These DNA methodologies can complement other methods (i.e. visual analysesand stomach contents analyses) in monitoring programs of penguins.

Reproductive investment during the chick-rearing period is an important contributor to lifetime fitness. Key to chick-rearing is the success of parental foraging, as food deliveries affect chick growth and survival up until fledging. For seabirds, oceanographic conditions including factors such as sea surface temperature are known to influence foraging decisions, but few studies have examined the physiological variables that might affect those decisions. We used global positioning systems (GPS), time-depth recorders (TDR), and physiological sampling techniques to explore links between ocean temperature, diving behavior, and foraging success in chick-rearing female macaroni penguins Eudyptes chrysolophus. We then explored correlations between these foraging variables and measures of individual physiological condition, specifically aerobic capacity (hematocrit) and metabolic state (corticosterone). In GPS-tracked penguins, 2 principal foraging tactics were observed: penguins made deep dives in cool, near-shore areas surrounding the breeding colony at Bird Island, South Georgia, or they traveled farther to dive shallower in warmer shelf-break areas. TDR-equipped penguins showed similar patterns. Blood sampling of TDR penguins at the onset of trips revealed strong positive correlations between hematocrit and the mean duration of foraging trips, the ocean temperature experienced during these trips, and the relative efficiency of foraging activity in terms of the number of foraging behaviors recorded per dive. These results suggest that aerobic capacity might be an important determinant of foraging trip range, as well as workload. Corticosterone was unrelated to diving behavior, which counters previous studies examining the effects of experimental increases of this hormone on foraging behavior, and we discuss reasons for this disparity.

Spatial and temporal variability in marine biological productivity may drive heterogeneity in seasonal resources available for marine animals in temperate waters. Migratory seabirds are expected to adjust their annual cycle of breeding activities and migratory movements to exploit seasonally available resources efficiently. We studied the movement and trophic position of rhinoceros auklets Cerorhinca monocerata breeding at Teuri Island, Japan Sea, during the nonbreeding and early breeding periods over 2 yr. After breeding, the auklets moved northward from the colony to the Sea of Okhotsk, where phytoplankton blooms enhanced biological productivity in autumn. The birds then moved southward to the southwestern Japan Sea (~1470 km from the colony), where major epipelagic fish and squid concentrations have been reported in winter. Stable isotope analyses suggest that the auklets fed on higher-trophic level prey, including fish and/or squid during the autumn and winter nonbreeding periods. The auklets moved northward and returned to the colony in mid-March. During the early breeding period, the birds foraged close to the colony (~380 km) on lower-trophic level prey including fish and/or krill, which were available during the spring phytoplankton bloom. The timing of the return migration does not match with the northward migration of warm-water anchovy, a profitable prey during summer, but may be related to timing the chick-rearing period to correspond with anchovy arrival. We suggest that rhinoceros auklets follow spatial and seasonal changes in prey availability by a distinctive ‘3-step’ migration (first northward, second southward, third northward) in the temperate marine system of the northwestern Pacific.

Knowing the spatial scales at which effective management can be implemented is fundamental for conservation planning. This is especially important for mobile species, which can be exposed to threats across large areas, but the space use requirements of different species can vary to an extent that might render some management approaches inefficient. Here the space use patterns of seabirds were examined to provide guidance on whether conservation management approaches should be tailored for taxonomic groups with different movement characteristics. Seabird tracking data were synthesised from 5419 adult breeding individuals of 52 species in ten families that were collected in the Atlantic Ocean basin between 1998 and 2017. Two key aspects of spatial distribution were quantified, namely how far seabirds ranged from their colony, and to what extent individuals from the same colony used the same areas at sea. There was evidence for substantial differences in patterns of space-use among the ten studied seabird families, indicating that several alternative conservation management approaches are needed. Several species exhibited large foraging ranges and little aggregation at sea, indicating that area-based conservation solutions would have to be extremely large to adequately protect such species. The results highlight that short-ranging and aggregating species such as cormorants, auks, some penguins, and gulls would benefit from conservation approaches at relatively small spatial scales during their breeding season. However, improved regulation of fisheries, bycatch, pollution and other threats over large spatial scales will be needed for wide-ranging and dispersed species such as albatrosses, petrels, storm petrels and frigatebirds. Fil: Oppel, Steffen. Royal Society For The Protection Of Birds; Fil: Bolton, Mark. Royal Society For The Protection Of Birds; Fil: Carneiro, Ana P.B.. Birdlife International; Fil: Dias, Maria P.. Birdlife International; Fil: Green, Jonathan A.. University of Liverpool; Reino Unido Fil: Masello, Juan F.. Justus Liebig University Giessen; Fil: Phillips, Richard A.. British Antarctic Survey; Fil: Owen, Ellie. Royal Society For The Protection Of Birds; Fil: Quillfeldt, Petra. Justus Liebig University Giessen; Fil: Beard, Annalea. Environmental And Natural Resources Directorate; Fil: Bertrand, Sophie. Universidad Federal Rural Pernambuco; Brasil. Centre National de la Recherche Scientifique. Institut de Recherche pour le Développement; Francia Fil: Blackburn, Jez. British Trust For Ornithology; Fil: Boersma, P. Dee. University Of Washington, Seattle; Fil: Borges, Alder. Projecto Vitó; Fil: Broderick, Annette C.. University of Exeter; Reino Unido Fil: Catry, Paulo. Ispa - Instituto Universitário; Portugal Fil: Cleasby, Ian. Royal Society For The Protection Of Birds; Fil: Clingham, Elizabeth. Environmental And Natural Resources Directorate; Fil: Creuwels, Jeroen. Naturalis Biodiversity Center; Fil: Crofts, Sarah. Falklands Conservation; Fil: Cuthbert, Richard J.. Royal Society For The Protection Of Birds; Fil: Dallmeijer, Hanneke. Veda Consultancy; Fil: Davies, Delia. University Of Cape Town; Fil: Davies, Rachel. Marinelife; Fil: Dilley, Ben J.. University Of Cape Town; Fil: Dinis, Herculano Andrade. Parque Natural Do Fogo; Fil: Dossa, Justine. Birdlife International; Fil: Dunn, Michael J.. British Antarctic Survey; Fil: Efe, Marcio A.. Universidade Federal de Alagoas; Brasil Fil: Fayet, Annette L.. University of Oxford; Reino Unido Fil: Figueiredo, Leila. Universidade Federal de Alagoas; Brasil Fil: Frederico, Adelcides Pereira. Projecto Vitó; Fil: Gjerdrum, Carina. Environment Canada; Canadá Fil: Godley, Brendan J.. University of Exeter; Reino Unido Fil: Granadeiro, José Pedro. Faculdade de Ciências, Universidade de Lisboa; Portugal Fil: Guilford, Tim. University of Oxford; Reino Unido Fil: Hamer, Keith C.. University Of Leeds; Fil: Hazin, Carolina. Birdlife International; Fil: Hedd, April. Environment Canada; Canadá Fil: Henry, Leeann. Environmental And Natural Resources Directorate; Fil: Hernández-Montero, Marcos. Projeto Biodiversidade; Fil: Hinke, Jefferson. Noaa Fisheries Service; Fil: Kokubun, Nobuo. National Institute Of Polar Research; Fil: Leat, Eliza. Ascension Island Government; Fil: Tranquilla, Laura McFarlane. Royal Society For The Protection Of Birds; . Environmental And Natural Resources Directorate; Fil: Metzger, Benjamin. Birdlife Malta; Malta Fil: Militão, Teresa. Universidad de Barcelona; España Fil: Montrond, Gilson. Projecto Vitó; Fil: Mullié, Wim. Veda Consultancy; Fil: Padget, Oliver. University of Oxford; Reino Unido Fil: Pearmain, Elizabeth J.. Birdlife International; Fil: Pollet, Ingrid L.. Bird Studies Canada; Canadá Fil: Pütz, Klemens. Antarctic Research Trust; Fil: Quintana, Flavio Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biología de Organismos Marinos; Argentina Fil: Ratcliffe, Norman. British Antarctic Survey; Fil: Ronconi, Robert A.. Environment Canada; Canadá Fil: Ryan, Peter G.. University Of Cape Town; Fil: Saldanha, Sarah. Universidad de Barcelona; España Fil: Shoji, Akiko. University of Oxford; Reino Unido Fil: Sim, Jolene. Ascension Island Government; Fil: Small, Cleo. Royal Society For The Protection Of Birds; Fil: Soanes, Louise. University of Liverpool; Reino Unido Fil: Takahashi, Akinori. National Institute Of Polar Research; Fil: Trathan, Phil. British Antarctic Survey; Fil: Trivelpiece, Wayne. Noaa Fisheries Service; Fil: Veen, Jan. Veda Consultancy; Fil: Wakefield, Ewan. University of Glasgow; Reino Unido Fil: Weber, Nicola. University of Exeter; Reino Unido. Ascension Island Government; Fil: Weber, Sam. Ascension Island Government; . University of Exeter; Reino Unido Fil: Zango, Laura. Universidad de Barcelona; España Fil: González-Solís, Jacob. Universidad de Barcelona; España Fil: Croxall, John. Birdlife International

Seabirds are increasingly threatened worldwide, with population declines for many species that are faster than in any other group of birds. Here the Important Bird Area (IBA) criteria recommended by BirdLife International were applied to a large tracking dataset collected from a range of seabirds, to identify areas of importance at an ocean basin scale. Key areas were identified using tracks obtained from both the breeding and non-breeding periods of 10 species that have different habitat requirements. These species range in their IUCN threat status from Least Concern to Critically Endangered. An evaluation of spatial overlap between the key areas for these species and the jurisdiction of Regional Fisheries Management Organisations (RFMOs), national Exclusive Economic Zones (EEZs) and other stakeholder bodies highlighted the major importance of the French EEZs (around Crozet, Kerguelen and Amsterdam Islands) for seabird conservation. The majority of the candidate marine IBAs that were identified were located in the High Seas, where Marine Protected Areas cannot easily be designated under existing international agreements, except in the Commission for the Conservation of Antarctic Marine Living Resources Convention Area. In the short term, it seems that only fisheries regulations (through international agreements) can bring about efficient protection for seabirds in the High Seas. The BirdLife IBA approach, although sensitive to heterogeneity in the data (species selected, inclusion of different life stages, years etc.), proved valuable for selecting important areas corresponding to large-scale oceanographic structures that are considered to be key foraging habitats for many species.

Physiological mechanisms mediating carryover effects, wherein events or activities occurring in one season, habitat, or life-history stage affect important processes in subsequent life-history stages, are largely unknown. The mechanism most commonly invoked to explain carryover effects from migration centres on the acquisition and utilization of resources (e.g. body mass, or individual 'condition'). However, other mechanisms are plausible, e.g. trade-offs reflecting conflict or incompatibility between physiological regulatory systems required for different activities or life-history stages (migration vs. reproduction). Here we show that in female black-browed albatrosses (Thalassarche melanophris) the decision to reproduce or to defer reproduction, made prior to their arrival at breeding colonies after long-distance migration, is associated with condition-related (body mass, hematocrit, hemoglobin concentrations) and hormonal (progesterone, testosterone, estrogen-dependent yolk precursors) traits. In contrast, reproductive success showed little association with condition but showed significant associations with the steroidogenic processes underlying follicle development. Specifically, success was determined by reproductive readiness via differences in steroid hormones and hormone-dependent traits. Successful albatrosses were characterized by high progesterone and high estradiol-dependent yolk precursor levels, whereas failed albatrosses had high testosterone and low yolk precursor levels. Results are discussed with reference to migratory carryover effects and how these can differentially affect the physiologies influencing reproductive decisions and reproductive success.

In avian species that have evolved life-history strategies wherein molt and breeding overlap, there are potential conflicts between the regulatory roles of baseline prolactin and corticosterone in parental care (positive) and moult (negative). We describe seasonal patterns of hormonal secretion, moult, and parental behaviour in sibling species of giant petrels (Macronectes spp.) which begin moult during the incubation/ early chick-rearing stage of reproduction. With the exception of male Southern giant petrels (Macronectes giganteus), prolactin secretion and moult in Northern (Macronectes halli) and female Southern giant petrels conformed to those observed in all other avian species, with the initiation of moult coincident with decreases from peak prolactin levels. However, male Southern giant petrels began moulting early in incubation when prolactin was increasing and had not yet peaked, which suggests a requirement of prolactin for incubation behaviour and a dissociation of prolactin from moult. Corticosterone showed little seasonal variation and no relationship with moult. When comparing prolactin, corticosterone, and moult in failed vs. active breeders, we found that failed breeding enabled a more rapid down-regulation of prolactin, thus facilitating a more rapid moult. We present specific examples of the behavioural ecology of giant petrels which we conclude help mediate any potential hormonal conflicts between parental care and moult.

It has long been held that Eudyptes penguins will only ever develop a maximum of two mature yolky follicles to match their invariant two-egg clutch, an idea inferred largely from egg removal studies. Combining our own data with those from a previous but rarely cited study and by applying these to a simple developmental model, we show that macaroni penguins (Eudyptes chrysolophus) develop up to four large, yolky vitellogenic follicles, and they do so despite the fact that they will never lay more than two eggs or rear more than one chick, a tactic that seems maladaptive given their realized reproductive success. We discuss these results within the context of the usual pattern of reproductive investment in Eudyptes penguins and suggest a broader significance to modes of clutch size determination among all penguins (order Sphenisciformes).

Long-distance migration enables many organisms to take advantage of lucrative breeding and feeding opportunities during summer at high latitudes and then to move to lower, more temperate latitudes for the remainder of the year. The latitudinal range of the Adelie Penguin (Pygoscelis adeliae) spans approximately 22 degrees. Penguins from northern colonies may not migrate, but due to the high latitude of Ross Island colonies, these penguins almost certainly undertake the longest migrations for the species. Previous work has suggested that Adelies require both pack ice and some ambient light at all times of year. Over a three-year period, which included winters of both extensive and reduced sea ice, we investigated characteristics of migratory routes and wintering locations of Adelie Penguins from two colonies of very different size on Ross Island, Ross Sea, the southernmost colonies for any penguin. We acquired data from 3-16 geolocation sensor tags (GLS) affixed to penguins each year at both Cape Royds and Cape Crozier in 2003-2005. Migrations averaged 12760 km, with the longest being 17 600 km, and were in part facilitated by pack ice movement. Trip distances varied annually, but not by colony. Penguins rarely traveled north of the main sea-ice pack, and used areas with high sea-ice concentration, ranging from 75% to 85%, about 500 km inward from the ice edge. They also used locations where there was some twilight (2-7 h with sun < 6 degrees below the horizon). We report the present Adelie Penguin migration pattern and conjecture on how it probably has changed over the past approximately 12000 years, as the West Antarctic Ice Sheet withdrew southward across the Ross Sea, a situation that no other Adelie Penguin population has had to confront. As sea ice extent in the Ross Sea sector decreases in the near future, as predicted by climate models, we can expect further changes in the migration patterns of the Ross Sea penguins.

Understanding the relationship between reproductive performance and food availability requires knowledge about many different variables, including such factors as the length of incubation shifts, provisioning rates and patterns, as well as how variability in these factors affects reproductive output. To examine some of the most important aspects of parental investment, we studied the provisioning behaviour and patterns of adult Southern Rockhopper Penguins Eudyptes chrysocome chrysocome breeding at Staten Island, Argentina. We investigated foraging trip duration, provisioning rates and chick survival using adult foraging patterns. Our results show that Rockhopper Penguins had clear sex-specific differences in their provisioning behaviour. Females provision chicks throughout chick rearing. By contrast, males provision chicks only during the creche stage and at a slightly lower rate than females during this period. Foraging trips increased in length as the breeding season progressed. Rockhopper Penguins from Staten Island performed longer trips throughout the breeding season than do other species of Eudyptes at several other locations. Our results also show differences in parental investment between years that were related to differences in chick survival. We suggest that this was most likely to be related to female rather than male foraging behaviour as only females showed inter-annual differences in their provisioning rates.

We used Argos satellite transmitters to monitor the movement and oceanographic habitats used by rockhopper penguins Eudyptes chrysocome chrysocome during their winter dispersal from Staten Island, Argentina, for 2002 (n = 10) and 2003 (n = 15). In both years penguins concentrated their activities to shallow and highly productive waters with temperatures ranging from 5 to 8°C. However, analysis of migration patterns, in conjunction with remotely-sensed sea surface temperature (SST) and chlorophyll a (chl a) concentration data, showed that habitat use and movement were substantially different for the 2 years. Both years were characterised by different oceanographic conditions; comparison of SST revealed colder temperatures in 2002 than the long-term average, while temperatures in 2003 were not significantly different from average conditions. The movement of rockhopper penguins differed between years: penguins migrated to the same general locations but used a larger number of foraging areas in 2002. They also spent less time travelling than in 2003. Moreover, we also found differences in adult survival or return rate and breeding success between years. Consequently, we conclude that during colder winters with more heterogeneous oceanographic conditions (e.g. 2002), penguins are better able to find enough food to achieve body condition for the following breeding season.

Knowledge of the spatial and temporal dynamics of foraging penguins is important to our understanding of the Southern Ocean marine ecosystem. We use satellite tracking to provide the first data on the distribution and behaviour of gentoo penguins (Pygoscelis papua) during the winter at South Georgia. Five penguins tracked from Bird Island remained close inshore, and although they did not return to the initial tagging site, they did appear to return to land each evening. They made diurnal trips to sea of similar distance from land as those during the breeding season, even though the constraints of chick rearing were absent. Despite potential greater flexibility in their responses to variations in prey availability in winter, the penguins still returned to land each night. This may reflect benefits from conserving energy by resting on land, possibly facilitating information exchange and avoiding predation. The distribution and behaviour of gentoo penguins during the winter enables efficient exploitation of a dynamic, patchy prey resource and may ultimately determine the timing of return to the colony, and onset of breeding in the following season.

Chinstrap penguins Pygoscelis antarctica are one of the major consumers of Antarctic krill Euphausia superba in the Southern Ocean. To examine their foraging strategy, we studied foraging trip patterns and diving behaviour of chinstrap penguins breeding at Signy Island, Antarctica, using time-depth recorders. Foraging trips of penguins could be divided into 2 groups, short diurnal (7.8 h) and longer overnight (19.9 h) trips, with diurnal trips (74%) being dominant in number (263 out of 355 trips). The diving depths of our study birds were much deeper (to 179 m) than previous studies on this species, with modal maximum dive depth at around 90 to 100 m. Diving patterns and profiles included typical pelagic dives, but also included series of consecutive square-wave shaped dives reaching similar maximum depth, the typical characteristics of benthic dives. These benthic-type dives were more abundant in diurnal foraging trips than overnight trips. Analysis of stomach contents showed that penguins on both types of trip fed almost exclusively on Antarctic krill. There was a positive relationship between indices of the proportion of benthic feeding and of foraging efficiency (stomach content mass divided by foraging trip duration). These results highlight the potential importance of benthic feeding on Antarctic krill, the first such recorded instance for chinstrap penguins. This previously undescribed foraging strategy by one of the major avian consumers of Antarctic krill provides a new insight into the predator-prey interactions of the Antarctic coastal marine ecosystem.

Corticosterone has received considerable attention as the principal hormonal mediator of allostasis or physiological stress in wild animals. More recently, it has also been implicated in the regulation of parental care in breeding birds, particularly with respect to individual variation in foraging behavior and provisioning effort. There is also evidence that prolactin can work either inversely or additively with corticosterone to achieve this. Here we test the hypothesis that endogenous corticosterone plays a key physiological role in the control of foraging behavior and parental care, using a combination of exogenous corticosterone treatment, time-depth telemetry, and physiological sampling of female macaroni penguins (Eudyptes chrysolophus) during the brood-guard period of chick rearing, while simultaneously monitoring patterns of prolactin secretion. Plasma corticosterone levels were significantly higher in females given exogenous implants relative to those receiving sham implants. Increased corticosterone levels were associated with significantly higher levels of foraging and diving activity and greater mass gain in implanted females. Elevated plasma corticosterone was also associated with an apparent fitness benefit in the form of increased chick mass. Plasma prolactin levels did not correlate with corticosterone levels at any time, nor was prolactin correlated with any measure of foraging behavior or parental care. Our results provide support for the corticosterone-adaptation hypothesis, which predicts that higher corticosterone levels support increased foraging activity and parental effort.

There was an error in the Author Contributions designations. The correct Author Contributions are: Conceived and designed the experiments: PF PT GK CP AHF. Performed the experiments: PF ML CP. Analyzed the data: PF ML GK AJF NR. Contributed reagents/materials/analysis tools: PF ML PM CP NR. Wrote the paper: PF PT GK BW ML PM. Provided data: PM AHF GK BW.

Where life-history stages overlap, there is the potential for physiological conflicts that might be important in mediating carryover effects. However, our knowledge of the specific physiological mechanisms underlying carryover effects remains rudimentary, and specific examples remain rare. Here we show that female macaroni penguins (Eudyptes chrysolophus) initiate vitellogenesis and yolk formation while at sea during return migrations to breeding colonies; yolk formation takes approximately 16 days, but females lay only 7-14 days after their return. Once on land, Eudyptes penguins show a unique reproductive pattern of extreme egg size dimorphism in which the smaller, first-laid A-egg is 55%-75% of the size of the larger B-egg. We show that the degree of egg size dimorphism is inversely correlated with time between arrival and laying; that is, females that begin reproductive development well in advance of their return produce more dimorphic eggs. Furthermore, late-arriving females that produce the most dimorphic eggs have lower plasma levels of the yolk precursor vitellogenin on arrival; that is, they show lower reproductive "readiness." These data support the hypothesis that extreme egg size dimorphism in Eudyptes penguins is due to a physiological constraint imposed by a migratory carryover effect and argue against small A-eggs having a specific, adaptive function.

Although penguins are key marine predators from the Southern Ocean, their migratory behaviour during the inter-nesting period remains widely unknown. Here, we report for the first time, to our knowledge, the winter foraging movements and feeding habits of a penguin species by using geolocation sensors fitted on penguins with a new attachment method. We focused on the macaroni penguin Eudyptes chrysolophus at Kerguelen, the single largest consumer of marine prey among all seabirds. Overall, macaroni penguins performed very long winter trips, remaining at sea during approximately six months within the limits of the Southern Ocean. They departed from Kerguelen in an eastward direction and distributed widely, over more than 3.10 6 km 2 . The penguins spent most of their time in a previously unrecognized foraging area, i.e. a narrow latitudinal band (47–49° S) within the central Indian Ocean (70–110° E), corresponding oceanographically to the Polar Frontal Zone. There, their blood isotopic niche indicated that macaroni penguins preyed mainly upon crustaceans, but not on Antarctic krill Euphausia superba , which does not occur at these northern latitudes. Such winter information is a crucial step for a better integrative approach for the conservation of this species whose world population is known to be declining.

The foraging strategy of many animals is thought to be determined by their past experiences. However, few empirical studies have investigated whether this is true in diving animals. We recorded three-dimensional movements and mouth-opening events from three Antarctic fur seals during their foraging trips to examine how they adapt their behaviour based on past experience—continuing to search for prey in the same area or moving to search in a different place. Each dive cycle was divided into a transit phase and a feeding phase. The linear horizontal distance travelled after feeding phases in each dive was affected by the mouth-opening rate during the previous 244 s, which typically covered two to three dive cycles. The linear distance travelled tended to be shorter when the mouth-opening rate in the previous 244 s was higher, i.e. seals tended to stay in the same areas with high prey-encounter rates. These results indicate that Antarctic fur seals follow decision-making strategies based on the past foraging experience over time periods longer than the immediately preceding dive.

Variability in the Southern Ocean is often characterized by fluctuations in the distribution and abundance of a single dominant zooplankton species, Antarctic krill Euphausia superba . The ability to sample krill in the diet of predators at temporal scales not available using conventional (i.e. ship-based) sampling methods has provided the basis for a re-evaluation of the role of high rates of growth and mortality, as well as recruitment variability, in generating variability in krill abundance at South Georgia. In addition, the use of a consistent index of krill population size composition from the diet of predators at South Georgia over the past decade has provided evidence for a relationship between sea-surface temperature and the level of krill recruitment. Predators that depend on krill not only show distinct behavioural responses to changes in krill abundance but also provide dietary data that help us to understand the mechanisms underlying the population dynamics of krill. Where the diet of predators includes commercial prey species, they can provide information on the key life-history variables of these species that are fundamental to reducing uncertainty in fisheries management models. VARIABILITY IN THE SOUTHERN OCEAN Understanding the causes and consequences of natural variability in marine ecosystems is a prerequisite to determining the nature and extent of changes of anthropogenic origin and is a central component of ecosystem-based approaches to fisheries management.