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As one of the best studied components of the Southern Ocean food web, Pygoscelis penguins serve as an important window into the larger marine ecosystem, but the patchiness and heterogeneity of the census data available have made it difficult to assess trends in a policy-accessible way. Here we introduce a Pygoscelis penguin-specific biodiversity index, the ‘Penguindex,’ using the framework of the Living Planet Index (LPI), distilling 40 year population trends of pygoscelid penguins for the first time into a single pan-Antarctic indicator for use by policymakers. We also calculate species- and region-specific indices from which discrete eras of population dynamics can be identified. These indices, similar to the LPI itself, do not provide estimates of changes in absolute abundance of species but, instead, reflect comparable population trends and the relative magnitude of these changes. We find that the Adélie Penguin (Pygoscelis adeliae) index was relatively stable across the Antarctic since 1980, with declines in regional indices across the Antarctic Peninsula region being contrasted by increases in regional indices for the Ross Sea and East Antarctica. The Chinstrap Penguin (Pygoscelis antarctica) index across the Antarctic declined by 61%. In stark contrast, the index for Gentoo Penguin (Pygoscelis papua) has increased seven-fold. Our analysis also identifies several marked eras of regional pygoscelid population change that may help identify key mechanistic drivers. We expect that the Penguindex will act as a useful reference tool for policymakers and hope that, by following this example, other taxonomic groups in the Antarctic might be tracked using the Living Planet Index framework. Importantly, our development of the Penguindex should facilitate the much-needed integration of Antarctic data into global biodiversity monitoring.

Background According to the literature review, this is the first study investigating tear production (TP) and intraocular pressure (IOP) in the Pygoscelis penguins living in their natural habitat. The study aimed to establish normal values for standard ocular tests in the genus Pygoscelis , namely, the Adélie ( Pygoscelis adeliae ), gentoo ( Pygoscelis papua ), and chinstrap ( Pygoscelis antarctica ) penguins, in four different islands of Antarctica. Sampling was made by specifically using the left eye of the penguins. The Schirmer's tear test type I (STT-I) and the Tonovet® (rebound tonometer) were used to measure the TP and the IOP, respectively. Results The mean TP and IOP values of 129 Adélie , chinstrap, gentoo, and 120 adult Adélie , gentoo penguins were determined as 10.2 ± 4.0 mm/min and 38.9 ± 13.2 mmHg, respectively. No statistical difference was detected between the penguin species for the mean IOP values, while the difference was determined in all the locations. However, statistical differences in the mean TP values were determined between all locations. Conclusion The results of this study provide a reference range of Schirmer's tear test (STT) and IOP values in Pygoscelis penguins and show that the IOP is significantly affected by locations. This result can be attributed to the harsh climatic conditions of the Antarctic Peninsula that change very quickly. The described data may help diagnose clinical pathological findings in Pygoscelis penguins. The STT and rebound tonometry appears to be safe and reproducible methods in Pygoscelis penguins, as the results were obtained quickly and were well tolerated by the birds. Based on our results, we propose that similar studies can be initiated in crowded colonies of three penguin species of this genus on the Antarctic Peninsula, the southern Shetland Islands, and other frequently visited islands in Antarctica. Highlights • This study is the first to investigate tear production (TP) and intraocular pressure (IOP) in Pygoscelis penguins. • TP value was obtained by Schirmer's tear test type I (STT- I), while the IOP was measured with the help of Tonovet® (rebound tonometer). • No clinical macroscopic findings affecting the eyelids, third eyelid, cornea, or ocular eye surface were found during the clinical examination of the penguins. • There was no difference in TP values between species of this genus and locations. There was no statistically significant difference between species in IOP mean values. However, a significant difference was noticed among the locations. • This study indicated that IOP in Pygoscelis penguins was significantly affected by location.

Climate change is a major threat to global biodiversity. Antarctic ecosystems are no exception. Investigating past species responses to climatic events can distinguish natural from anthropogenic impacts. Climate change produces ‘winners’, species that benefit from these events and ‘losers’, species that decline or become extinct. Using molecular techniques, we assess the demographic history and population structure of Pygoscelis penguins in the Scotia Arc related to climate warming after the Last Glacial Maximum (LGM). All three pygoscelid penguins responded positively to post-LGM warming by expanding from glacial refugia, with those breeding at higher latitudes expanding most. Northern ( Pygoscelis papua papua ) and Southern ( Pygoscelis papua ellsworthii ) gentoo sub-species likely diverged during the LGM. Comparing historical responses with the literature on current trends, we see Southern gentoo penguins are responding to current warming as they did during post-LGM warming, expanding their range southwards. Conversely, Adélie and chinstrap penguins are experiencing a ‘reversal of fortunes’ as they are now declining in the Antarctic Peninsula, the opposite of their response to post-LGM warming. This suggests current climate warming has decoupled historic population responses in the Antarctic Peninsula, favoring generalist gentoo penguins as climate change ‘winners’, while Adélie and chinstrap penguins have become climate change ‘losers’.

Ecologically similar marine species inhabiting the same areas compete for food resources. Such competition is reduced by resource-partitioning strategies that may affect physiology. For instance, diet and feeding strategies may affect the antioxidant defences or the production of reactive oxygen species. Oxidative stress is defined as the imbalance between pro-oxidants and antioxidant defences. If such an imbalance favours the former, this can lead to oxidative damage, and oxidative stress increases. However, to our knowledge, how free-ranging animals adjust their oxidative status in relation to their foraging habitats, diet and dietary antioxidants has not yet been studied. Penguins are an interesting biological model for such a comparison because their diet, based on krill, fish and/or cephalopods, presents strong variation in dietary antioxidant content. We therefore examined trophic level (δ15N), foraging habitat (δ13C), dietary antioxidants (retinol, α-tocopherol and astaxanthin) and oxidative status (plasma non-enzymatic antioxidant capacity and oxidative damage) in pygoscelid penguins (chinstrap Pygoscelis antarcticus, gentoo P. papua and Adélie P. adeliae) breeding in Antarctica. We found interspecific differences in all variables analysed except α-tocopherol. Gentoo penguins exploited more cephalopods and fish in coastal and benthic habitats, Adélies showed an intermediate position, whereas chinstraps foraged more on krill and fish in pelagic waters. Dietary antioxidant levels showed specific patterns resulting in relationships with prey items. However, we did not find any clear relationships between dietary antioxidants and species-specific antioxidant capacity, suggesting the importance of endogenously produced antioxidants. Oxidative status appeared to be differently related to foraging strategy and antioxidant capacity in each species.

Gentoo penguins (Pygoscelis papua) are found across the Southern Ocean with a circumpolar distribution and notable genetic and morphological variation across their geographic range. Whether this geographic variation represents species‐level diversity has yet to be investigated in an integrative taxonomic framework. Here, we show that four distinct populations of gentoo penguins (Iles Kerguelen, Falkland Islands, South Georgia, and South Shetlands/Western Antarctic Peninsula) are genetically and morphologically distinct from one another. We present here a revised taxonomic treatment including formal nomenclatural changes. We suggest the designation of four species of gentoo penguin: P. papua in the Falkland Islands, P. ellsworthi in the South Shetland Islands/Western Antarctic Peninsula, P. taeniata in Iles Kerguelen, and a new gentoo species P. poncetii, described herein, in South Georgia. These findings of cryptic diversity add to many other such findings across the avian tree of life in recent years. Our results further highlight the importance of reassessing species boundaries as methodological advances are made, particularly for taxa of conservation concern. We recommend reassessment by the IUCN of each species, particularly P. taeniata and P. poncetii, which both show evidence of decline. Gentoo penguins (Pygoscelis papua) are found across the Southern Ocean with a circumpolar distribution and notable genetic and morphological variation across their geographic range. Here, we show that four distinct populations of gentoo penguins (Iles Kerguelen, Falkland Islands, South Georgia, and South Shetlands/Western Antarctic Peninsula) are genetically and morphologically distinct from one another. We suggest the designation of four species of gentoo penguin: P. ellsworthi in the South Shetland Islands/Western Antarctic Peninsula, P. taeniata in Iles Kerguelen, and P. poncetii in South Georgia with the Falkland Islands retaining P. papua.

Surveying seabirds in polar latitudes can be challenging due to sparse human populations, lack of infrastructure and the risk of disturbance to wildlife or damage to habitats. Counting populations using un-crewed aerial vehicles (UAVs) is a promising approach to overcoming these difficulties. However, a careful validation of the approach is needed to ensure comparability with counts collected using conventional methods. Here, we report on surveys of three Antarctic bird species breeding on Signy Island, South Orkney Islands; Chinstrap (Pygoscelis antarctica) and Gentoo (Pygoscelis papua) Penguins, and the South Georgia Shag (Leucocarbo atriceps georgianus). We show that images from low-altitude UAV surveys have sufficient resolution to allow separation of Chinstrap Penguins from contiguously breeding Adélie Penguins (Pygoscelis adéliae), which are very similar in appearance when viewed from overhead. We compare data from ground counts with manual counts of nesting birds on images collected simultaneously by low-altitude aerial photography from multi-rotor UAVs at the same colonies. Results at this long-term monitoring site confirmed a continued population decline for Chinstrap Penguins and increasing Gentoo Penguin population. Although both methods provided breeding pair counts that were generally within ~ 5%, there were significant differences at some locations. We examine these differences in order to highlight potential biases or methodological constraints that should be considered when analysing similar aerial census surveys and comparing them with ground counts.

We report long-term changes in population size of three species of sympatrically breeding pygoscelid penguins: Adélie (Pygoscelis adeliae), chinstrap (Pygoscelis antarctica) and gentoo (Pygoscelis papua ellsworthii) over a 38 year period at Signy Island, South Orkney Islands, based on annual counts from selected colonies and decadal all-island systematic counts of occupied nests. Comparing total numbers of breeding pairs over the whole island from 1978/79 to 2015/16 revealed varying fortunes: gentoo penguin pairs increased by 255%, (3.5% per annum), chinstrap penguins declined by 68% (-3.6% per annum) and Adélie penguins declined by 42% (-1.5% per annum). The chinstrap population has declined steadily over the last four decades. In contrast, Adélie and gentoo penguins have experienced phases of population increase and decline. Annual surveys of selected chinstrap and Adélie colonies produced similar trends from those revealed by island-wide surveys, allowing total island population trends to be inferred relatively well. However, while the annual colony counts of chinstrap and Adélie penguins showed a trend consistent in direction with the results from all-island surveys, the magnitude of estimated population change was markedly different between colony wide and all island counts. Annual population patterns suggest that pair numbers in the study areas partly reflect immigration and emigration of nesting birds between different parts of the island. Breeding success for all three species remained broadly stable over time in the annually monitored colonies. Breeding success rates in gentoo and chinstrap penguins were strongly correlated, despite the differing trends in population size. This study shows the importance of effective, standardised monitoring to accurately determine long-term population trajectories. Our results indicate significant declines in the Adélie and chinstrap penguin populations at Signy Island over the last five decades, and a gradual increase in gentoo breeding pairs.

Background Energy landscapes provide an approach to the mechanistic basis of spatial ecology and decision-making in animals. This is based on the quantification of the variation in the energy costs of movements through a given environment, as well as how these costs vary in time and for different animal populations. Organisms as diverse as fish, mammals, and birds will move in areas of the energy landscape that result in minimised costs and maximised energy gain. Recently, energy landscapes have been used to link energy gain and variable energy costs of foraging to breeding success, revealing their potential use for understanding demographic changes. Methods Using GPS-temperature-depth and tri-axial accelerometer loggers, stable isotope and molecular analyses of the diet, and leucocyte counts, we studied the response of gentoo ( Pygoscelis papua ) and chinstrap ( Pygoscelis antarcticus ) penguins to different energy landscapes and resources. We compared species and gentoo penguin populations with contrasting population trends. Results Between populations, gentoo penguins from Livingston Island (Antarctica), a site with positive population trends, foraged in energy landscape sectors that implied lower foraging costs per energy gained compared with those around New Island (Falkland/Malvinas Islands; sub-Antarctic), a breeding site with fluctuating energy costs of foraging, breeding success and populations. Between species, chinstrap penguins foraged in sectors of the energy landscape with lower foraging costs per bottom time, a proxy for energy gain. They also showed lower physiological stress, as revealed by leucocyte counts, and higher breeding success than gentoo penguins. In terms of diet, we found a flexible foraging ecology in gentoo penguins but a narrow foraging niche for chinstraps. Conclusions The lower foraging costs incurred by the gentoo penguins from Livingston, may favour a higher breeding success that would explain the species’ positive population trend in the Antarctic Peninsula. The lower foraging costs in chinstrap penguins may also explain their higher breeding success, compared to gentoos from Antarctica but not their negative population trend. Altogether, our results suggest a link between energy landscapes and breeding success mediated by the physiological condition.

Fast climate changes in the western Antarctic Peninsula are reducing krill density, which along with increased fishing activities in recent decades, may have had synergistic effects on penguin populations. We tested that assumption by crossing data on fishing activities and Southern Annular Mode (an indicator of climate change in Antarctica) with penguin population data. Increases in fishing catch during the non-breeding period were likely to result in impacts on both chinstrap (Pygoscelis antarcticus) and gentoo (P. papua) populations. Catches and climate change together elevated the probability of negative population growth rates: very high fishing catch on years with warm winters and low sea ice (associated with negative Southern Annular Mode values) implied a decrease in population size in the following year. The current management of krill fishery in the Southern Ocean takes into account an arbitrary and fixed catch limit that does not reflect the variability of the krill population under effects of climate change, therefore affecting penguin populations when the environmental conditions were not favorable.

Specialization is a common mechanism of niche differentiation that can lead to ecological co-existence among species. However, species with specialized habitat or dietary requirements often exhibit a high degree of sensitivity to environmental change. Understanding patterns of specialization and niche segregation among Antarctic marine predators is of increased importance because of recent climate-driven reductions in a key prey species, Antarctic krill Euphausia superba. We examined the stomach contents and stable isotope values of sympatric chinstrap Pygoscelis antarctica and gentoo P. papua penguins across 5 breeding seasons at Cape Shirreff, Livingston Island, Antarctica. Our goal was to examine foraging niche segregation and the degree of specialization between species during the chick-rearing period. Dietary and isotopic foraging niches indicated consistent niche partitioning with higher krill consumption and greater use of offshore foraging habitats by chinstrap relative to gentoo penguins. While chinstrap penguin diets were dominated by krill with little variation, gentoo penguins exhibited broader dietary and isotopic niches with a higher degree of variation. There was little evidence that shifts in the availability of adult krill influenced penguin diets or foraging niches during our study, though the contrasting foraging strategies identified provide insight into the differing population trends observed between penguin species. The narrower foraging niche observed in declining chinstrap penguin populations indicates that they are likely highly sensitive to declines in the abundance of Antarctic krill. In contrast, the generalist niche exhibited by recently expanding gentoo penguin populations is likely better suited to the rapidly changing environmental conditions in the Antarctic Peninsula.