Geology topics

David G. Ainley

Publications and source records attributed to David G. Ainley.

At least 19 recordsLinked to original sources

USGS2026

Importance of fish in the diet of Adélie penguins across multiple life stages

Over recent decades, the Adélie penguin ( Pygoscelis adeliae ) population has grown across most of its range, the exception being the northern coast of the western Antarctic Peninsula (WAP). In the Ross Sea, the very large Cape Crozier colony grew to reach ~9% of the global population. Demographic factors driving the Cape Crozier trend have yet to be identified. However, low chick fledging mass - a negative influence in the northern WAP where the diet is mostly less-energy-dense krill - is not showing an effect in the Cape Crozier colony. Previously, we hypothesized that Cape Crozier fledglings, and post-breeding adults, must be finding sufficient higher-quality prey once free of the prey-depleted colony foraging area, with subsequent higher survival. Here we explore penguin diet within and outside the colony foraging area using stable isotope analysis (SIA) of feathers: those grown by post-breeding adults outside the foraging area, prior to moult, compared to those of near-fledged chicks raised on meals obtained within the foraging area. Second, we explore whether a major difference occurs between breeding and post-breeding diet of adults from a small, nearby colony (Cape Royds) that exploits a smaller, little-depleted preyscape. Finally, we compare the results to SIA analyses published by others to explore whether the pre-moult diet of Ross Island adults, mostly foraging within the north-eastern Ross Sea, compares with that of adults nesting in the southern WAP (Bellingshausen Sea coast). At the latter, populations are not decreasing, with diet containing an appreciable contribution of fish. The results confirmed that fish contributed greatly to chick diets at both Ross Island colonies (δ 15 N 10.6–11.4). Once adults were released from central-place foraging, SIA levels (δ 15 N 9.7–12.9) were similar to those of the southern WAP. Foraging on energy-dense fish in coastal Antarctic waters could be one reason Adélie penguins are among the most abundant and therefore most ecologically successful penguin species.

Antarctic Science↗

USGS2026

Novel avian papillomaviruses identified in a south polar skua sampled on Ross Island, Antarctica

Papillomaviruses are small circular DNA viruses that infect epithelial cells of their hosts. Avian papillomaviruses are poorly sampled/documented compared to those infecting humans. We used a viral metagenomic approach to identify viruses from the oral swab taken from a deceased south polar skua ( Stercorarius maccormicki ) found at Cape Royds, Ross Island, Antarctica in late 2024. We identified three papillomaviruses and determined their complete genomes, Stercorarius maccormicki papillomavirus (SmacPV) 1-3. SmacPV1 is the most divergent of the three SmacPVs, sharing 62% genome-wide pairwise identity to SmacPV2 and SmacPV3 and <63.5% to other avian papillomaviruses. The genomes of SmacPV2 and SmacPV3 represent two new papillomavirus types sharing 82.4% genome-wide pairwise identity with each other and <72% to other papillomaviruses. SmacPV2 and SmacPV3 phylogenetically cluster with sequences of the Rissa tridactyla papillomavirus 1 from black-legged kittiwake ( Rissa tridactyla ), Larus smithsonianus papillomavirus 1 from American herring gull ( Larus smithsonianus ) and Fratercula arctica papillomavirus 1 from Atlantic puffin ( Fratercula arctica ), and they collectively represent a new papillomavirus species. These are the first papillomaviruses to be identified in Stercorarius spp . and add to the handful of known papillomaviruses in identified avian species. We also expand the known host range of papillomaviruses in Antarctic animals, which previously included Adélie penguins ( Pygoscelis adeliae ), Weddell seals ( Leptonychotes weddellii ), Antarctic fur seals ( Arctocephalus gazella ), leopard seals ( Hydrurga leptonyx ) and emerald notothen ( Trematomus bernacchii ).

Archives of Virology↗

USGS2026

Timing the tuxedo transformation: Moult phenology reflects breeding investment and intrinsic constraints in Adélie penguins

Vertebrate life histories are often divided into distinct periods, with the breeding season typically receiving the most research attention. For polar seabirds, non-breeding phases like moult remain understudied, despite their importance for survival and overall fitness. Adélie penguins ( Pygoscelis adeliae ) replace their highly specialized feathers during an approximately 19-day annual moult, typically carried out while fasting on sea ice. The required fast and elevated metabolic rate may create a significant energetic bottleneck. We analysed data from geolocating dive recorders deployed on known-age Adélie penguins and non-known-age pairs from two Ross Island colonies over three winters (2017–2019). Moult start date was influenced by breeding success, intrinsic factors (age, sex) and extrinsic factors (year), with males, older birds and successful breeders moulting later. Moult duration varied primarily with individual ID, though later initiation correlated with shorter duration, particularly when located further south. Moult duration was longer in the western Ross Sea, a region that was used exclusively by males. The association between moult start date and duration may lead to differential sex and breeding status effects, with older males more likely to face a trade-off between successful breeding and self-maintenance tasks like feather replacement.

Proceedings of the Royal Society B↗

USGS2025

Diversity of polyomaviruses and papillomaviruses in penguins from eastern and western Antarctica

Polyomaviruses and papillomaviruses are icosahedral viruses with small circular dsDNA genomes. Limited information on their diversity and evolution in avian hosts is available, with even less known regarding Antarctic penguins. Prior to this study, only one polyomavirus and two papillomaviruses had been identified in Adélie penguins ( Pygoscelis adeliae ). To expand our knowledge of these viruses in Antarctic penguins, we collected faecal and cloacal swab samples from 246 Adélie penguins over 3 breeding seasons (2021–2024) and 10 emperor penguins ( Aptenodytes forsteri ) during the 2023–2024 season on Ross Island (Ross Sea). Additionally, we sampled 66 Adélie, 40 chinstrap ( Pygoscelis antarcticus ) and 71 gentoo ( Pygoscelis papua ) penguins during the 2022–2023 season across various sites on the Antarctic Peninsula. All samples were screened for papillomaviruses and polyomaviruses. We identified 31 polyomaviruses in Adélie, gentoo and chinstrap penguins and 4 papillomaviruses in Adélie penguins sampled in both eastern and western Antarctica. The 31 penguin polyomaviruses belong to a single species but form four distinct variants that are host species specific with strong geographic clustering. The four papillomaviruses represent three different types, of which two are new types from Adélie penguins sampled on Yalour Island in the West Antarctic Peninsula. Co-occurrence of two polyomavirus variants was identified in two individual gentoo penguins. Both of these variants appear to be circulating in gentoo penguins at Cierva Cove, Hope Bay in Trinity Peninsula along the Antarctic Peninsula, and at Hannah Point on Livingstone Island and Stranger Point on King George Island in the South Shetland Islands. Here, we expand the known diversity, host and geographical ranges of penguin polyomaviruses and, together with a previously identified polyomavirus on Ross Island from 2012 to 2013, show that they form five distinct lineages. The four papillomaviruses identified in this study, together with two previously identified from Ross Island in 2012 and 2013 breeding seasons, show substantial diversity reflecting four papillomavirus types across three viral species and two distinct genera. Continued surveillance and viral genomic analysis across a larger geographical framework will help understand the evolution, transmission and incidence rates of these viruses.

Microbial Genomics↗

USGS2024

Sex-specific recruitment rates contribute to male-biased sex ratio in Adélie penguins

Sex-related differences in vital rates that drive population change reflect the basic life history of a species. However, for visually monomorphic bird species, determining the effect of sex on demographics can be a challenge. In this study, we investigated the effect of sex on apparent survival, recruitment, and breeding propensity in the Adélie penguin ( Pygoscelis adeliae ), a monochromatic, slightly size dimorphic species with known age, known sex, and known breeding history data collected during 1996–2019 ( n = 2127 birds) from three breeding colonies on Ross Island, Antarctica. Using a multistate capture–mark–recapture maximum-likelihood model, we estimated apparent survival (

Ecology and Evolution↗

USGS2024

Going with the floe: Sea-ice movement affects distance and destination during Adélie penguin winter movements

Seasonal migration, driven by shifts in annual climate cycles and resources, is a key part of the life history and ecology of species across taxonomic groups. By influencing the amount of energy needed to move, external forces such as wind and ocean currents are often key drivers of migratory pathways exposing individuals to varying resources, environmental conditions, and competition pressures impacting individual fitness and population dynamics. Although wildlife movements in connection with wind and ocean currents are relatively well understood, movements within sea-ice fields have been much less studied, despite sea ice being an integral part of polar ecology. Adélie penguins ( Pygoscelis adeliae ) in the southern Ross Sea, Antarctica, currently exist at the southernmost edge of their range and undergo the longest (~12,000 km) winter migration known for the species. Within and north of the Ross Sea, the Ross Gyre drives ocean circulation and the large-scale movement of sea ice. We used remotely sensed sea-ice movement data together with geolocation-based penguin movement data to test the hypothesis that penguins use gyre-driven sea-ice movement to aid their migration. We found that penguins traveled greater distances when their movement vectors were aligned with those of sea ice (i.e., ice support) and the amount of ice support received depended on which route a penguin took. We also found that birds that took an eastern route traveled significantly further north in two of the 3 years we examined, coinciding with higher velocities of sea ice in those years. We compare our findings to patterns observed in migrating species that utilize air or water currents for their travel and with other studies showing the importance of ocean/sea-ice circulation patterns to wildlife movement and life history patterns within the Ross Sea. Changes in sea ice may have consequences not only for energy expenditure but, by altering migration and movement pathways, to the ecological interactions that exist in this region.

Ecology↗

USGS2023

High-resolution recording of foraging behaviour over multiple annual cycles shows decline in old Adélie penguins’ performance

Age-related variation in foraging performance can result from both within-individual change and selection processes. These mechanisms can only be disentangled by using logistically challenging long-term, longitudinal studies. Coupling a long-term demographic data set with high-temporal-resolution tracking of 18 Adélie penguins ( Pygoscelis adeliae , age 4–15 yrs old) over three consecutive annual cycles, we examined how foraging behaviour changed within individuals of different age classes. Evidence indicated within-individual improvement in young and middle-age classes, but a significant decrease in foraging dive frequency within old individuals, associated with a decrease in the dive descent rate. Decreases in foraging performance occurred at a later age (from 12–15 yrs old to 15–18 yrs old) than the onset of senescence predicted for this species (9–11 yrs old). Foraging dive frequency was most affected by the interaction between breeding status and annual life-cycle periods, with frequency being highest during returning migration and breeding season and was highest overall for successful breeders during the chick-rearing period. Females performed more foraging dives per hour than males. This longitudinal, full annual cycle study allowed us to shed light on the changes in foraging performance occurring among individuals of different age classes and highlighted the complex interactions among drivers of individual foraging behaviour.

Proceedings of the Royal Society B↗

USGS2023

Faster growth and larger size at crèche onset are associated with higher offspring survival in Adélie Penguins

We conducted the first assessment of Adélie Penguin ( Pygoscelis adeliae ) chick survival that accounts for imperfect resighting. We found that when chicks are larger in size when they enter the crèche stage (the period when both parents forage at the same time and chicks are left relatively unprotected), they have a higher probability of survival to fledging. We investigated the relationships between growth, crèche timing, and chick survival during one typical year and one year of reduced food availability. Chicks that hatched earlier in the season entered the crèche stage older, and chicks that both grew faster and crèched older entered the crèche at a larger size. These relationships were stronger in the year of reduced food availability. Thus, parents increased their chicks’ chance of fledging if they provided sufficient food for faster growth rates and/or extended the length of the brood-guarding period. Early nest initiation (i.e., early hatching) provided parents with the opportunity to extend the guard period and increase chick survival. However, to extend the guard stage successfully, they must provide larger meals and maintain higher chick growth rates, even if just one parent at a time is foraging, which previous work has shown is not possible for all individuals. We show that the factors governing tradeoffs in chick-rearing behavior of Adélie Penguin parents may vary in accord with environmental conditions, a result from which we can better understand species’ adaptations to environmental changes.

Ornithology↗

USGS2021

The influence of subcolony-scale nesting habitat on the reproductive success of Adélie penguins

Group-size variation is common in colonially breeding species, including seabirds, whose breeding colonies can vary in size by several orders of magnitude. Seabirds are some of the most threatened marine taxa and understanding the drivers of colony size variation is more important than ever. Reproductive success is an important demographic parameter that can impact colony size, and it varies in association with a number of factors, including nesting habitat quality. Within colonies, seabirds often aggregate into distinct groups or subcolonies that may vary in quality. We used data from two colonies of Adélie penguins 73 km apart on Ross Island, Antarctica, one large and one small to investigate (1) How subcolony habitat characteristics influence reproductive success and (2) How these relationships differ at a small (Cape Royds) and large (Cape Crozier) colony with different terrain characteristics. Subcolonies were characterized using terrain attributes (elevation, slope aspect, slope steepness, wind shelter, flow accumulation), as well group characteristics (area/size, perimeter-to-area ratio, and proximity to nest predators). Reproductive success was higher and less variable at the larger colony while subcolony characteristics explained more of the variance in reproductive success at the small colony. The most important variable influencing subcolony quality at both colonies was perimeter-to-area ratio, likely reflecting the importance of nest predation by south polar skuas along subcolony edges. The small colony contained a higher proportion of edge nests thus higher potential impact from skua nest predation. Stochastic environmental events may facilitate smaller colonies becoming “trapped” by nest predation: a rapid decline in the number of breeding individuals may increase the proportion of edge nests, leading to higher relative nest predation and hindering population recovery. Several terrain covariates were retained in the final models but which variables, the shapes of the relationships, and importance varied between colonies.

Scientific Reports↗

USGS2021

Effects of diet and provisioning behavior on chick growth in Adélie Penguins (Pygoscelis adeliae)

When provisioning chicks, parents trade-off their time, energy, and other resources to maximize reproductive success. As parents adjust investment to maximize their fitness, impacts on offspring growth can occur. We investigated provisioning and chick growth of Adélie Penguins ( Pygoscelis adeliae ) at one of the largest colonies (∼175,000 pairs), during one year of normal chick growth and survival and in a year which, by chance, was characterized by low chick growth and survival (“difficult” year). We measured daily average amount and quality of food delivered, as well as foraging-trip duration, and compared them to chick mass and skeletal growth during two years of contrasting conditions. We used mixed-effects models to test the prediction that increased parental investment would lead to increased growth rates, while accounting for confounding effects. There was no evidence of an effect of parent age. All provisioning measures predicted growth of at least one morphological character but, especially during the year of normal reproductive success, no provisioning measure strongly predicted growth across most morphological characters. However, during the difficult year parental investment positively affected growth rates, especially for males that were fed relatively more fish. The observed variation in growth rates between males and females, and between years of contrasting apparent resource availability, was large enough to lead to size differences that may subsequently affect post-fledging survival and ultimately population processes.

Waterbirds↗

USGS2021

Modeling at-sea density of marine birds to support renewable energy planning on the Pacific outer continental shelf of the contiguous United States

This report describes the at-sea spatial distributions of marine birds in Pacific OCS waters off the contiguous U.S. (Figure 1.1) to inform marine spatial planning in the region. The goal was to estimate long-term average spatial distributions for marine bird species using all available science-quality transect survey data and numerous bathymetric, oceanographic, and atmospheric predictor variables. We developed seasonal habitat-based spatial models of the at-sea distribution for 33 individual species and 13 taxonomic groups of marine birds throughout the study region. A statistical modeling framework was used to estimate numerical relationships between bird sighting data (i.e., standardized counts) and a range of temporal (e.g., Pacific Decadal Oscillation [PDO] index), spatially static (e.g., depth), and spatially dynamic (e.g., sea surface chlorophyll-a concentration) environmental variables. The estimated relationships were then used to predict spatially explicit long-term average density (individuals per km 2 ) throughout the study area for each species/group in each of four seasons. Bird sighting data came from multiple scientific survey programs and consisted of at-sea counts of birds collected between 1980 and 2017 using boat-based and fixed-wing aerial transect survey methods. Spatial environmental variables were derived from remote sensing satellite data and an ocean dynamics model.

California, Oregon, Washington↗

USGS2020

Rockhopper Penguin–Imperial Cormorant mixed colonies in the Falkland Islands: A stroke of luck for late breeders

Mixed-species colonies occur frequently, especially among seabirds, and may provide mutual benefits among associated species including antipredator advantages. The “protector” species in such associations may provide early warning signals or by aggressively defending their own nests, may expel predators from the area. We explored costs and benefits to Rockhopper Penguins ( Eudyptes chrysocome ) in relation to offspring production in both monospecific colonies and those mixed with Imperial Cormorants ( Phalacrocorax atriceps ) at Saunders Island (Falkland Islands), emphasizing differences in predation pressure. We considered behavioral responses of chicks (in crèches), as well as differences in their nutritional condition, morphometric measurements, and survival compared among different breeding colonies. Our study revealed a paradox: High-quality adult penguins, those arriving early and occupying lower-elevation sites closer to the coast, produced better-nourished chicks earlier in the season. However, they averaged half the number of chicks fledged, compared to breeders that arrived later in the season. Late breeders were forced by unavailability of optimal habitat to nest in more elevated areas, forming mixed colonies with cormorants, which, in turn, provided them with protection from nest predators. This study provides an example of the role of luck in nature, and how it may compensate for differences in individual fitness.

Ecosphere↗

USGS2019

Identification of a novel Adélie penguin circovirus at Cape Crozier (Ross Island, Antarctica)

Understanding the causes of disease in Antarctic wildlife is crucial as many of these species are already threatened by environmental changes brought about by climate change. In recent years, Antarctic penguins have been showing signs of an unknown pathology: a feather disorder characterised by missing feathers resulting in exposed skin. During the 2018-19 austral summer breeding season at Cape Crozier colony on Ross Island, Antarctica, for the first time we observed an Adlie penguin chick missing down over most of its body. A guano sample was collected from the nest of the featherless chick and, using high throughput sequencing we identified a novel circovirus. Using abutting primers, we amplified the full genome, which we cloned, and Sanger sequenced to determine the complete genome of the circovirus. The Adlie penguin guano-associated circovirus genome shares <67% genome-wide nucleotide identity to other circoviruses, representing a new species of circovirus, therefore we named it penguin circovirus (PenCV). Using the same primer pair, we screened 25 previously collected cloacal swabs taken at Cape Crozier from known-age adult Adlie penguins during the 2014-15 season displaying no clinical signs of feather-loss disorder. Three of the 25 samples (12%) were positive for a PenCV, whose genome shared >99% pairwise identity to the one identified in 2018-19. This is the first report of a circovirus associated with a penguin species and could be a possible etiological agent of the feather-loss disorder in Antarctic penguins.

Viruses↗

USGS2019

Evidence of age-related improvement in the foraging efficiency of Adélie penguins

Age variation in reproductive performance is well-documented but the mechanisms underlying this variation remain unclear. Foraging efficiency is likely to be a key source of demographic variation as it determines the amount of energy that can be invested in fitness-related activities. Evidence of age-related changes in the foraging efficiency of adult seabirds is scarce and inconsistent. We investigated the effects of age on the foraging efficiency of breeding Adélie penguins, a relatively short-lived seabird species, in order to gain a broader perspective on the processes driving variation in ageing rates. We found support for a positive effect of age, either linear or levelling off at old ages, on both our proxies for daily catch rate and catch per unit effort. Across all age classes, males were more performant foragers than females. We found no strong evidence for differing ageing patterns between sexes or individual quality levels, and no evidence for senescence. We infer that continuous individual improvement could be responsible for a larger amount of the variation in foraging efficiency with age at our study site, compared with selective disappearance of underperforming phenotypes. The different results reported by other studies highlight the need to conduct longitudinal studies across a range of species in different environments.

Scientific Reports↗

USGS2018

Energetic fitness: Field metabolic rates assessed via 3D accelerometry complement conventional fitness metrics

Evaluating the fitness of organisms is an essential step towards understanding their responses to environmental change. Connections between energy expenditure and fitness have been postulated for nearly a century. However, testing this premise among wild animals is constrained by difficulties in measuring energy expenditure while simultaneously monitoring conventional fitness metrics such as survival and reproductive output. We addressed this issue by exploring the functional links between field metabolic rate (FMR), body condition, sex, age and reproductive performance in a wild population. We deployed 3D accelerometers on 115 Adélie penguins Pygoscelis adeliae during four breeding seasons at one of the largest colonies of this species, Cape Crozier, on Ross Island, Antarctica. The demography of this population has been studied for the past 18 years. From accelerometry recordings, collected for birds of known age and breeding history, we determined the vector of the dynamic body acceleration (VeDBA) and used it as a proxy for FMR. This allowed us to demonstrate relationships among FMR, a breeding quality index (BQI) and body condition. Notably, we found a significant quadratic relationship between mean VeDBA during foraging and BQI for experienced breeders, and individuals in better body condition showed lower rates of energy expenditure. We conclude that using FMR as a fitness component complementary to more conventional fitness metrics will yield greater understanding of evolutionary and conservation physiology.

Functional Ecology↗

USGS2018

Post-fledging survival of Adélie Penguins at multiple colonies: chicks raised on fish do well

We assessed whether the mass of Adélie penguin Pygoscelis adeliae fledglings at 3 colonies of markedly disparate size on Ross Island, Ross Sea, correlated with their eventual return as subadults. We compared our results with those from Anvers Island, Bellingshausen Sea. Colony sizes at Ross Island have been increasing, contrary to decreasing size at Anvers Island. At Ross Island, during the month prior to fledging, chick diet consisted equally of energy-dense Antarctic silverfish Pleuragramma antarctica and less-caloric crystal krill Euphausia crystal-lorophias , while at Anvers Island the diet was principally Antarctic krill E. superba . At Ross Island, the mass of fledglings who subsequently returned (mean ± SE: 3.4 ± 0.0411 kg) exceeded that of those not seen again (3.2 ± 0.0251 kg), compared to Anvers Island (3.2 vs. 3.0 kg, respectively). At Ross Island, fledging mass was inversely related to colony size and, at the largest colony, fledging mass decreased as the colony grew. Average mass of returnees at the largest colony was less than the mass at Anvers Island for those fledglings that did not return. The mean proportion of fish in the chicks’ diet decreased at the largest Ross Island colony over time, as did fledging mass. We hypothesize that intraspecific competition increased along with colony size, decreasing the availability of fish. We further hypothesize that at the large Ross Island colony, post-fledging penguins must be finding adequate prey, and more energy-dense fish, just outside the colony’s foraging area to explain opposing trends in colony trajectories.

Beaufort Island, Ross Island, Ross Sea↗

USGS2017

Unique genome organization of non-mammalian papillomaviruses provides insights into the evolution of viral early proteins

The family Papillomaviridae contains more than 320 papillomavirus types, with most having been identified as infecting skin and mucosal epithelium in mammalian hosts. To date, only nine non-mammalian papillomaviruses have been described from birds ( n = 5), a fish ( n = 1), a snake ( n = 1), and turtles ( n = 2). The identification of papillomaviruses in sauropsids and a sparid fish suggests that early ancestors of papillomaviruses were already infecting the earliest Euteleostomi. The Euteleostomi clade includes more than 90 per cent of the living vertebrate species, and progeny virus could have been passed on to all members of this clade, inhabiting virtually every habitat on the planet. As part of this study, we isolated a novel papillomavirus from a 16-year-old female Adélie penguin ( Pygoscelis adeliae ) from Cape Crozier, Ross Island (Antarctica). The new papillomavirus shares ∼64 per cent genome-wide identity to a previously described Adélie penguin papillomavirus. Phylogenetic analyses show that the non-mammalian viruses (expect the python, Morelia spilota , associated papillomavirus) cluster near the base of the papillomavirus evolutionary tree. A papillomavirus isolated from an avian host (Northern fulmar; Fulmarus glacialis ), like the two turtle papillomaviruses, lacks a putative E9 protein that is found in all other avian papillomaviruses. Furthermore, the Northern fulmar papillomavirus has an E7 more similar to the mammalian viruses than the other avian papillomaviruses. Typical E6 proteins of mammalian papillomaviruses have two Zinc finger motifs, whereas the sauropsid papillomaviruses only have one such motif. Furthermore, this motif is absent in the fish papillomavirus. Thus, it is highly likely that the most recent common ancestor of the mammalian and sauropsid papillomaviruses had a single motif E6. It appears that a motif duplication resulted in mammalian papillomaviruses having a double Zinc finger motif in E6. We estimated the divergence time between Northern fulmar-associated papillomavirus and the other Sauropsid papillomaviruses be to around 250 million years ago, during the Paleozoic-Mesozoic transition and our analysis dates the root of the papillomavirus tree between 400 and 600 million years ago. Our analysis shows evidence for niche adaptation and that these non-mammalian viruses have highly divergent E6 and E7 proteins, providing insights into the evolution of the early viral (onco-)proteins.

Virus Evolution↗

USGS2016

South Polar Skua breeding populations in the Ross Sea assessed from demonstrated relationship with Adélie Penguin numbers

In the Ross Sea region, most South Polar Skuas ( Stercorarius maccormicki ) nest near Adélie Penguin ( Pygoscelis adeliae ) colonies, preying and scavenging on fish, penguins, and other carrion. To derive a relationship to predict skua numbers from better-quantified penguin numbers, we used distance sampling to estimate breeding skua numbers within 1000 m of 5 penguin nesting locations (Cape Crozier, Cape Royds, and 3 Cape Bird locations) on Ross Island in 3 consecutive years. Estimated numbers of skua breeding pairs were highest at Cape Crozier (270,000 penguin pairs; 1099 and 1347 skua pairs in 2 respective years) and lowest at Cape Royds (3000 penguin pairs; 45 skua pairs). The log–log linear relationship ( R 2 = 0.98) between pairs of skuas and penguins was highly significant, and most historical estimates of skua and penguin numbers in the Ross Sea were within 95 % prediction intervals of the regression. Applying our regression model to current Adélie Penguin colony sizes at 23 western Ross Sea locations predicted that 4635 pairs of skuas now breed within 1000 m of penguin colonies in the Ross Island metapopulation (including Beaufort Island) and northern Victoria Land. We estimate, using published skua estimates for elsewhere in Antarctica, that the Ross Sea South Polar Skua population comprises ~50 % of the world total, although this may be an overestimate because of incomplete data elsewhere. To improve predictions and enable measurement of future skua population change, we recommend additional South Polar Skua surveys using consistent distance-sampling methods at penguin colonies of a range of sizes.

Polar Biology↗