A
A
Piotr Jan Angiel1 - Corresponding authorA
A
AnnaGasekPiotr1✉Emailpiotr.angiel@aer.ca
HorzelaElżbietaŁepkowska1
KrzysztofMajchrowska1,2✉Emailelzbieta.majchrowska@us.edu.plEmailkrzysztof.migala@uwr.edu.pl
DominikaMigała3
TadeuszRupp-Janecka1,4✉Emaild.rupp-janecka@nencki.edu.pl
GrzegorzSobczak1
Wierzbicki1,5✉Emailgrzegorz_wierzbicki@sggw.edu.pl
1Alberta Geological Survey250 5 St SWT2P 0R4CalgaryABCanada
2Institute of Earth Sciences, Faculty of Natural SciencesUniversity of Silesia in KatowiceBędzińska 6041-200SosnowiecPoland
3Institute of Geography and Regional DevelopmentUniversity of Wrocławpl. Uniwersytecki 150-137WrocławPoland
4Instytut Biologii Doświadczalnej im. Marcelego Nenckiego PANul. Ludwika Pasteura 302-093WarsawPoland
5Department of Hydraulics, Water and Sanitary Engineering, Institute of Environmental EngineeringUniversity of Life Sciences WULS-SGGWNowoursynowska 16602-787Warsaw, WarsawPoland
Anna Gasek
Piotr Horzela
Elżbieta Łepkowska (Majchrowska)2
Krzysztof Migała3
Dominika Rupp-Janecka 4
Tadeusz Sobczak
Grzegorz Wierzbicki5
1 Alberta Geological Survey, 250 5 St SW, Calgary, AB T2P 0R4, Canada, piotr.angiel@aer.ca, Corresponding author:
2 Institute of Earth Sciences, Faculty of Natural Sciences, University of Silesia in Katowice, Będzińska 60, 41–200 Sosnowiec, Poland, elzbieta.majchrowska@us.edu.pl
3 University of Wrocław, Institute of Geography and Regional Development, pl. Uniwersytecki 1, 50–137 Wrocław, Poland, krzysztof.migala@uwr.edu.pl
4 Instytut Biologii Doświadczalnej im. Marcelego Nenckiego PAN, ul. Ludwika Pasteura 3, 02–093 Warsaw, Poland, d.rupp-janecka@nencki.edu.pl
5 University of Life Sciences WULS-SGGW, Department of Hydraulics, Water and Sanitary Engineering, Institute of Environmental Engineering, Warsaw, Nowoursynowska 166, 02-787 Warsaw, Poland, grzegorz_wierzbicki@sggw.edu.pl
EFFECTS OF SNOW COVER ON NESTING AND REPRODUCTIVE SUCCESS IN GENTOO (PYGOSCELIS PAPUA) AND ADÉLIE (PYGOSCELIS ADELIAE) PENGUINS AT LIONS RUMP, KING GEORGE ISLAND, WEST ANTARCTICA
SUMMARY
This study examines how prolonged snow cover and meltwater affect breeding behavior and success in Gentoo (Pygoscelis papua) and Adélie (Pygoscelis adeliae) penguins. We monitored nearly 7,000 nests at Lions Rump, King George Island, where both species breed sympatrically, across two seasons with contrasting snow cover: a relatively snow-free 2008/09 season and a snow-heavy 2009/10 season.
While penguin population changes and trends have been widely studied, the effects of extreme snow conditions—such as abnormally thick cover during the onset and incubation periods—on the breeding success of Gentoo and Adélie penguins nesting in the same colonies remain poorly understood.
These anomalous conditions strongly influenced breeding outcomes by delaying nest initiation and increasing habitat instability during incubation and chick-rearing. In response to extensive snow cover during the 2009/10 season, Gentoo penguins shifted their nest-site distribution, concentrating on elevated, snow-free bedrock and moraine exposures while abandoning snow-covered beach terraces and low-elevation valley sites. In contrast, Adélie penguins largely retained their traditional elevated bedrock nesting areas with minimal spatial adjustment. Despite these behavioral differences, both species experienced delayed breeding, increased nest attrition, and reduced clutch sizes under snow stress. Gentoo penguins exhibited greater sensitivity to these conditions, with more variable breeding success and lower chick survival. Adélie penguins, by comparison, maintained stable chick survival and stronger nest-site fidelity, indicating greater resilience to snow-induced environmental stress. Importantly, Gentoo penguins also demonstrate significant interannual variability in breeding chronology and flexible nest-site selection, which may buffer reproductive success under varying environmental conditions. The pronounced nest loss and spatial reorganization in Gentoo penguins reflect their heightened vulnerability to snow accumulation and meltwater exposure, whereas Adélie penguins, though affected, sustained more consistent nesting patterns and reproductive outcomes.
These findings highlight the vulnerability of Antarctic seabirds to shifts in snow dynamics and emphasize the ecological importance of microhabitat resilience and species-specific behavioral strategies in coping with environmental variability.
A
INTRODUCTION
At Lions Rump, King George Island (Fig. 1), the penguin rookery is characterized by diverse nesting habitats, limited human disturbance, and relatively low predation pressure from avian predators on land—providing suitable conditions for analyzing the incubation period. Climate changes are well documented in the Antarctic Peninsula regions and linked to impacts on biota, including breeding penguins. A number of environmental factors may influence fluctuations in population sizes, breeding biology, and breeding success in Adélie (Pygoscelis adeliae) and Gentoo (Pygoscelis papua) penguins. The most important factors are those related to weather and ice conditions, particularly air temperature at the start of the breeding season, wind speed, and snow cover (Ainley & Leresche, 1973; Lynch et al., 2009).
Gentoo penguins, native to the milder sub-Antarctic climate, exhibit less specific nest-site selection compared to Adélie penguins, which are evolutionarily adapted to cope with drifting snow and harsh, short summers typical of the Antarctic continent (Ainley & Leresche, 1973; Bost & Jouventin, 1990a; Volkman & Trivelpiece, 1981). Given these ecological differences, Gentoo penguins were expected to be more vulnerable to prolonged snow cover than Adélie penguins. However, recent long-term data from King George Island suggest that Gentoo penguins may possess an adaptive advantage through behavioral plasticity. Hinke et al. (2012) demonstrated that Gentoo penguins exhibit flexible clutch initiation timing in response to environmental variability, which buffers their reproductive success even in years with elevated snowfall. In contrast, Adélie penguins showed reduced chick survival when breeding occurred outside a narrow optimal window. These findings suggest that phenological flexibility may play a critical role in shaping species-specific resilience to climatic stressors. Moreover, Juáres et al. (2013) reported significant interannual variability in breeding chronology and flexible nest-site selection in Gentoo penguins at King George Island, highlighting their ability to adjust reproductive strategies under variable snow conditions.
Long-term studies at Stranger Point, about 30 km southwest of Lions Rump, have documented significant shifts in breeding chronology and population dynamics in both species in response to snow-related environmental stressors (Juáres et al., 2013; Juáres et al., 2015). Research between 2007/08 and 2010/11 highlighted pronounced interannual and seasonal variability in breeding chronology and nest-site selection. Gentoo penguins demonstrated behavioral flexibility by adjusting nest-site location and reproductive scheduling in response to changing snow conditions, while Adélie penguins exhibited sensitivity in chick survival when breeding occurred outside optimal windows. These findings provide a broader regional context for interpreting short-term responses observed at Lions Rump. These patterns emphasize that snow cover and thaw time act as immediate drivers of breeding success in mixed-species colonies (Juáres et al., 2013).
To examine how these ecological differences manifest under varying snow conditions, we analyzed two contrasting breeding seasons at Lions Rump: one characterized by minimal snow accumulation (2008/09), and another marked by persistent snow cover throughout the incubation period (2009/10). We studied seasonal variation in the onset of the breeding season, nest-site characteristics (including geomorphological position, nest altitude, mean distance from the landing beach, and nest dispersion), nest attrition rates, breeding success, and meteorological data including temperature, wind speed, and snow cover thickness. This seasonal comparison allowed us to assess how snow-related environmental stress influenced nest-site distribution, breeding behavior, and reproductive success in both species.
Pronounced interannual variability in breeding success at Lions Rump appears closely tied to differences in snow conditions across seasons, affecting both species. The 2006/07 and 2008/09 seasons were largely snow-free, allowing for uninterrupted nesting and relatively stable reproductive output. In contrast, the snow-affected seasons of 2007/08 and 2009/10 disrupted colony establishment through flooded or obscured nesting sites. Adélie penguins showed marked reductions in chick survival and breeding success under these conditions, while Gentoo penguins maintained nesting activity by shifting to higher or less snow-prone areas. Adélie penguins, in particular, showed greater sensitivity to these conditions, with reduced chick survival and lower breeding success. Gentoo penguins demonstrated greater flexibility in nest-site selection but still experienced impacts from heavy snow accumulation. These patterns are consistent with observations by Juáres et al. (2013), who reported that interannual shifts in breeding chronology and nest-site choice strongly influence reproductive outcomes in Gentoo penguins. These alternating seasonal conditions highlight snowfall as a key driver of short-term fluctuations in reproductive performance and underscore species-specific differences in adaptability to snow-related habitat constraints.
STUDY AREA AND METHODS
Climate
The monitoring area at Lions Rump, King George Bay, is located at 62°08′S, 58°08′W within Antarctic Specially Protected Area No. 151 (ASPA-151; Fig. 1). King George Island is located in an area of highly dynamic and climatically sensitive conditions. The South Shetland Islands lie between the Drake Passage to the north and the Bransfield Strait to the south, resulting in a predominance of maritime characteristics shaped by air masses moving mainly from west to east. The atmospheric circulation is highly dynamic, producing significant variability in weather throughout the year and between years. Multi-year average air temperatures at stations in Admiralty Bay were − 1.7°C (1986–2010) at Ferraz and − 1.6°C (1977–1998; Kejna, 1999) at Arctowski, with consistently high humidity (82.3% at Arctowski) and average annual wind speeds of 6–6.5 m/s. Hurricane-force winds (> 30 m/s, gusts up to 80 m/s) are frequently observed (e.g., Wierzbicki, 2009; Angiel et al., 2010).
Summer temperatures at King George Island are typically above 0°C, allowing snow cover at lower elevations to melt completely. Periodic warming events—observed in nearly every month—along with strong foehn winds, limit the buildup of thick snow. At sea level, snow may also melt entirely during winter due to the advection of warm, humid air masses (Rachlewicz, 1997). Snow cover is not commonly measured at each station. At Arctowski, measurements are available for 2008/09 and 2009/10, obtained at a beach terrace near the station at altitude of 2 m a.s.l. Snow cover is highly variable and difficult to measure accurately, as snowfall often occurs during fast-moving weather systems accompanied by strong winds. Wind redistributes snow, so resulting accumulation reflects both fresh snowfall and drift. Broad hilltops exposed to wind typically have thin or no snow cover—these are preferred Adélie penguin nesting sites—while leeward slopes and depressions can accumulate deeper snow. Beach terraces provide relatively averaged snow thickness values, although these also reflect a combination of snowfall and wind-driven redistribution.
Fig. 1
(A) Map of the South Atlantic Ocean, showing locations mentioned in text; (B) Map of King George Island and Lions Rump, glaciers (light grey) and ice-free areas (black), showing locations mentioned in text: 1 Bellingshausen Station and Fildes Peninsula; 2 Arctowski Station; 3 Keller Peninsula (Ferraz Station), 4 Stranger Point.
Study Area
King George Island lies near a biologically significant boundary: the northern limit of pack ice, marking the northern extent of breeding zones for peri-Antarctic and continental breeders such as Adélie penguins, and the southernmost range of sub-Antarctic Gentoo penguins (Stenhouse, 1970). All three Pygoscelis penguin species nest on King George Island. In the mid-1980s, the island hosted approximately 350,910 pairs of Chinstrap penguins (P. antarctica), 65,300 pairs of Adélie penguins, and 11,430 pairs of Gentoo penguins (Trivelpiece et al., 1987).
Monitoring Program
Scouting trips to Lions Rump were conducted in December 2006 (snow-free season) and December 2007 (11–19 December; snow-affected season), with observations and photographic records collected during both trips. The first trip allowed direct counts and mapping of nest subgroups, whereas the second trip relied primarily on photographic documentation due to persistent snow cover.
A systematic penguin monitoring program was initiated in October 2008 and continued through subsequent breeding seasons. GPS mapping of nesting groups was performed during the 2008/09 (mild spring and summer) and 2009/10 (adverse snow conditions) seasons. Comparative analyses revealed spatial changes in breeding group distribution, demonstrating species-specific responses to snow cover. Maps of breeding groups from these seasons were prepared (Fig. 2).
Fig. 2
Lions Rump rookery (Shoreline, hydrographic elements and contour lines based on Battke, Z. and Cisak, J., 1988: Cape Lions Rump, 1:5 000 scale, Institute of Ecology, Polish Academy of Sciences, Warsaw).
A – Season 2008/9: Snow cover about the time of the peak of egg laying and nest sites distribution; 1 - detailed monitoring site of Adélie Penguins, 2 - detailed monitoring site of Gentoo Penguins (“Little Finger”),
B – Season 2009/10: Snow cover about the time of the peak of egg laying in 2009/10 and nest sites distribution; 1 - detailed monitoring site of Adélie Penguins, 2 - detailed monitoring site of Gentoo Penguins (“Ornithologist Moraine”), 3 - detailed monitoring site of Gentoo Penguins (“Ring Finger”),
C – Annual change in Gentoo Penguins nesting groups distribution from 2008/9 to 2009/10,
D – Hypsometry map of Lions Rump rookery.
Nest Distribution and Habitat Use
Adélie and Gentoo penguins co-occurred at Lions Rump without competition for nesting sites. In 2008/09, 97% of breeding Adélie penguins (4,216 pairs) were concentrated in a large nesting group on bedrock outcrops. with the remaining 3% in small mixed groups with Gentoo penguins. Gentoo penguins (2,996 nests) occupied a wider range of habitats, including glacial moraine tops, elevated bedrock, raised beaches, hillocks in valleys, moraine slopes, and saddles between hills.
Reference breeding sites were selected for detailed monitoring: for Adélie penguins, a section of the largest nesting group was observed (109 nests in 2008/09, 96 nests in 2009/10); for Gentoo penguins, a sub-colony known as “Little Finger” (121 nests) was monitored in 2008/09. In 2009/10, this site was not re-established due to thick snow cover; 84 nest sites in nearby moraine areas were monitored instead. Observations focused on the incubation and early chick-rearing stages.
Breeding Success and Data Collection
A
Nest censuses for both species were conducted approximately 1–2 weeks after the respective peaks of egg laying (Table 1). For Gentoo penguins, total nest numbers were recalculated two and four weeks after the initial count to determine daily nest attrition rates. Breeding success was calculated by dividing the number of chicks counted 3–4 weeks after hatching by the total number of nests recorded 1–2 weeks after peak laying. Additionally, 206 Adélie penguin chicks were weighed in 2008/09 and 200 in 2009/10. To minimize disturbance, no flipper bands or foraging sampling were used, and each monitoring team was limited to two people per season. All birds were of unknown age, and food availability was inferred solely from the body weight of fledged Adélie chicks.
Meteorological Data Sources and Geomorphological Mapping
No meteorological station exists at Lions Rump. Data for the 2008/09 and 2009/10 seasons were obtained from Arctowski and Ferraz stations. During geomorphological mapping of ASPA-151 in 2009 (Angiel, unpublished data), the rookery area was characterized in detail, including landforms and nest-site features. For each nesting group, altitude and shortest distance to the sea were calculated from the colony center. A one-way ANOVA was used to compare changes in these parameters between seasons.
RESULTS
The results focus on the 2008/09 and 2009/10 breeding seasons, selected for in-depth analysis of meteorological and biological data, with earlier seasons (2006/07–2007/08) used only as supplementary references.
Meteorological conditions during the 2008/09 and 2009/10 breeding seasons and annual context
2008/09
The year 2008 was characterized by mild weather compared to previous years, with an average annual temperature of -0.7°C at Ferraz Station (Fig. 3). Particularly high temperatures were observed in the spring: September and October with monthly averages 3.8°C and 1.7°C higher, respectively, than the multi-year average from Ferraz Station (1986–2010). In 2008, 559.2 mm of precipitation were recorded at Arctowski Station. Snow cover was generally thin throughout the year, with a maximum of 31 cm in early July. Positive temperatures observed for several days each month during winter prevented continuous snow cover. September had no snow, and in October, a single snowstorm on 2–3 October deposited 25 cm, which melted completely by 11 October. From then until the end of January, snow cover was largely absent (Fig. 4).
2009/10
Compared to 2008, the average temperature in 2009 was − 2.6°C (Ferraz Station), with a particularly cold period from May to November (Fig. 3). Lower temperatures in October and November delayed snowmelt. Precipitation was lower than in the previous year (400 mm at Arctowski Station), but below-freezing temperatures in winter and spring preserved the snow cover until late December (Fig. 4). At the beginning of the 2009/10 breeding season in late October, flat beach terraces at Lions Rump were still covered with about 50–60 cm of snow. Only hilltops had patches of snow-free ground due to wind removal of snow. Valleys accumulated deep snow drifts, and nesting sites from the previous season could not be re-established in Moon Valley (e.g., “Little Finger,” Fig. 2A). Thick snow forced resting and breeding Southern Elephant Seals (Mirounga leonina) to move from snow-covered beaches to snow-free ground, inadvertently destroying some penguin nests, and several elephant seal pups became trapped in snow pits, resulting in their death. Snow on beaches melted by late December, restoring access to low-elevation nesting areas.
Fig. 3
Average temperature and wind speed at Ferraz Station in Admiralty Bay in the season 2008/9, 2009/10 and the multi-year average (1986–2010). Data source: Projeto de Meteorologia Antàrtica (Project on Antarctic Meteorology: http://antartica.cptec.inpe.br/)
Fig. 4
Daily averages of a) air temperature (°C), b) wind speed (m/s), and c) snow cover thickness (cm) at Arctowski Station between 1st October and 31st January in 2008/9 and 2009/10 season (several data gaps occurred due to outages at the meteorological station).
Nest-site characteristics of Adélie and Gentoo penguins on Lions Rump
Breeding sites of Adélie penguins were almost entirely concentrated on wind-swept Lions Rump bedrock exposures, with a single large nesting site comprising 96% of the local breeding population. The remaining 4% of nesting sites were shared with Gentoo penguins and were strongly affected by snow conditions in 2009/10. Notably, Adélie penguins largely remained on the same nest sites in both 2008/09 and 2009/10, showing minimal dispersal in response to snow cover.
In contrast, Gentoo penguin breeding sites were distributed across a wide area encompassing various landforms (Table 2). During the 2008/09 breeding season, the rookery consisted of approximately 70 nest groups averaging 50–60 nests, with the largest group comprising 256 nests. Moraine tops hosted 42.8% of Gentoo penguin nests. Elevated bedrock exposures, slopes, and flat beach terraces contributed between 14% and 16.2%. Flat saddles between hills and hummocks in valleys and depressions contributed 10% and 11.9%, respectively. Many isolated single-nest sites, described as “satellite nests,” comprised 5.9% (n = 176) of the total breeding population. Overall, nest density was relatively low, reflecting the species’ more dispersed nesting strategy.
During the snowy 2009/10 season, the reduction in snow-free areas led to less dispersed nest sites, with only 1.7% (n = 45) classified as satellite nests. Moraines remained the most favored landforms, hosting 44.6% of nests. Elevated bedrock exposures increased in prominence, reaching 26.2% of nest sites. Conversely, valleys and flat beaches were largely snow-covered, resulting in decreased nest contributions of 3.8% and 3.4%, respectively. Nest-sites on flat saddles and slopes also saw reduced contribution due to snow cover (Table 2). These spatial shifts indicate that Gentoo Penguins were forced into fewer snow-free microhabitats, likely contributing to reduced breeding success in the snowy 2009/10 season.
Nest-site shifts in altitude and distance from landing beaches in Gentoo penguins
A one-way analysis of variance (ANOVA; Bewick et al., 2004) was applied to compare differences in nest-site parameters between warm and cold seasons. The significance of changes in altitude and distance from landing beaches for Gentoo penguins was analyzed. A statistically significant (P < .0001) shift was observed toward higher elevations and greater distances from landing beaches in the colder season (Fig. 5 and Fig. 6.). For many Gentoo penguin breeding pairs, access to nesting sites shifted from flat, low-lying areas such as beaches, valley bottoms, and small moraine hills near sea level to higher-elevation moraines and bedrock outcrops on Lions Rump, situated about 20–40 m a.s.l.
Fig. 5
Summary of Gentoo Penguins nests distribution as a percentage of altitudes above the sea level in the season 2008/9 and 2009/10.
Fig. 6
Summary of Gentoo Penguins nests distribution and the distance from the closest landing beach in the season 2008/9 and 2009/10.
In the snowier season, the total number of Gentoo penguin nests dropped by 22.2% compared to the warmer season. The largest decreases were observed on flat beach terraces and in valley bottoms. On narrow moraine tops, nest numbers increased only in newly established sites on “Ornithologist Moraine” and “Green Moraine” (Fig. 2C) compared to 2008/09. The most significant increase in nest numbers was noted on elevated bedrock exposures, rising from 14.6% to 26.2% (Table 2).
The change in Gentoo penguin nesting sites was significant in the colder, snowier season. Nest altitude increased from 14.97 m to 18.5 m, and mean distance from landing beaches increased from 86.6 m to 94.4 m (Table 1). Newly colonized areas were primarily higher moraines and bedrock exposures on Lions Rump (20–40 m asl). Pebbles and rocks for nest construction were less abundant in these newly colonized sites compared to areas used in previous seasons (Figs. 7 & 8).
Note
Adélie penguins remained on the same bedrock sites as in 2008/09 and 2009/10, showing no comparable shift in nest elevation or distance from landing beaches.
A
B
Fig. 7
Gentoo Penguins nesting sites (n = 69) on a beach terrace in 2008/9 (A), and (B) in 2009/10 (n = 63), note that in 2009/10 nests are directly on snow, and substrate with pebbles is under the snow cover.
A
B
Fig. 8
Overview of southeastern part of rookery at Lions Rump: (A) on November 7th, 2008; and on November 17th, 2009 (B).
Breeding biology and success in 2008/09 and 2009/10
In 2008/09, both species laid eggs almost synchronously (Table 3), with peaks on 26–27 October. The total nest number in the Gentoo penguin rookery, measured 12 days after the laying peak, showed an average nest attrition rate of 0.31% per day (compared to the multi-year average of 0.6% per day; Lynch et al. 2009). For Adélie penguins, the nest attrition rate was 0.3% per day (0.9% per day average; Lynch et al. 2009).
In 2009/10, a significant delay in the start of the breeding season was observed. October was colder (average − 2.6°C at Ferraz) and snow cover on flat beach terraces at Lions Rump reached 50–60 cm, comparable to the 65 cm recorded at Arctowski Station, despite its location 18 km away. The peak of egg laying was delayed by 14 days for Adélie penguins and 27 days for Gentoo penguins compared to the previous year. The colony-wide attrition rate for Gentoo penguins, measured 13 days after the laying peak, was 0.89% per day—nearly triple the rate from the previous season. Adélie penguins also experienced increased nest loss, with a rate of 0.46% per day.
In 2008/09, more than 88% of nests in monitoring sites contained two eggs one week after the peak of egg laying (Table 4). The mean clutch size was 1.8, resulting in high breeding success for both species. In contrast, in 2009/10, only 64% of Adélie and 57% of Gentoo penguin nests contained two eggs one week after peak laying. During the first two weeks of chick rearing, Adélie penguin chick survival was 94.8% in 2008/09 and 93.8% in 2009/10. Gentoo penguins showed lower survival in the snowy season (92.8% compared to 82%). Notably, 2009/10 survival for Gentoo penguins was lower than the colony average because the monitored site included moraine areas with higher attrition rates and lower breeding success.
Between the 2008/09 and 2009/10 breeding seasons, overall breeding success declined significantly in both species (Table 3). Adélie penguin success dropped from 1.16 to 0.93 chicks per nest, while Gentoo penguin success decreased from 1.20 to 0.94 chicks per nest.
For Gentoo penguins, breeding success in 2009/10 varied across different parts of the colony. Bedrock exposure sites maintained relatively high success rates: Lion’s Arm (1.17 chicks/nest; 440 nests), Lion’s Rump (1.21 chicks/nest; 136 nests), and Angiel’s Arm moraine (0.96 chicks/nest; 194 nests). In contrast, lower success was observed in other moraine areas: Green Moraine (0.44 chicks/nest; 51 nests) and Ornithologist Moraine (0.60 chicks/nest; 95 nests).
Comparison of fledged Adélie penguin weights between breeding seasons showed that fledglings in the colder 2009/10 season were 6.4% lighter than those in 2008/09.
DISCUSSION
Breeding Success in Context
Long-term assessment of breeding success at Lions Rump is limited, as annual monitoring only began in 2008/09. However, Korczak-Abshire et al. (2013) provide a 2001–2010 overview of colony size and breeding success, showing average fledging rates of approximately 1.15 chicks per nest for Adélie penguins and 1.18 for Gentoo penguins, consistent with other colonies. Comparative data from other colonies show that average breeding success for Adélie and Gentoo penguins typically fluctuates around 1 ± 0.1 chicks per nest (Ainley 2002; Quintana & Cirelli 2000; Pistorius et al. 2010). In favorable years, success may exceed 1.2 chicks per nest, while adverse seasons can drop below 0.8 or result in total breeding failure (Croxall & Prince 1979; Robertson 1986).
At Lions Rump, breeding success in 2008/09 was relatively high—1.16 chicks per nest for Adélie penguins and 1.20 for Gentoo penguins. In contrast, the colder 2009/10 season saw reduced success: 0.93 for Adélie and 0.94 for Gentoo penguins. Despite greater delays in clutch initiation and substantial nest-site reorganization, Gentoo penguins maintained similar success rates to Adélie penguins.
This seasonal decline was primarily driven by reduced hatching success, likely linked to adverse weather and persistent snow cover during incubation. Chick survival remained high in both years, reinforcing the interpretation that snow-related impacts were concentrated in the early reproductive phase. Similar patterns have been documented elsewhere; for example, at Palmer Station in 2001, meltwater from accumulated snow flooded nests, leading to deferred breeding and reduced reproductive output (Massom et al. 2006).
Climate Warming and Ecological Shifts
Recent climate warming in the western Antarctic Peninsula has triggered substantial ecological shifts, including increased atmospheric and sea-surface temperatures (Smith et al. 1999; Vaughan et al. 2003; Meredith & King 2005), reduced sea-ice extent (Fraser et al. 1992; Stammerjohn et al. 2008), and altered prey dynamics such as declining krill abundance (Atkinson et al. 2004; Reiss et al. 2008). As highlighted in the IPCC Special Report and supported by Thomas et al. (2008), rising temperatures in the Antarctic Peninsula have increased the capacity of air masses to hold moisture, leading to more frequent and intense snow accumulation events. These regional climate trends may be interrupted by unusually cold and snow-heavy onsets of breeding seasons, such as the 2009/10 season at Lions Rump, potentially altering or disturbing long-term population trends in penguin colonies —making it crucial to understand in detail how such snow-related interruptions affect reproductive success.
Long-term observations indicate a correlation between climate warming in the western Antarctic Peninsula region and concurrent changes in penguin populations, notably a decrease in Adélie penguins and an increase in Gentoo penguins (e.g., Trivelpiece et al. 2011; Cimino et al. 2016). While Gentoo penguins have shown resilience through flexible foraging strategies and reduced dependence on sea ice (Miller et al. 2009; Forcada et al. 2006), their reproductive success remains vulnerable to terrestrial constraints, particularly increased snow accumulation.
Breeding Season Initiation and Phenological Flexibility
At the onset of each breeding season, penguins face a decision that is not merely physiological but shaped by a complex interplay of environmental cues, social dynamics, and individual condition. This decision is influenced by the presence and behavior of other birds, environmental factors, and physical condition—including body mass and shape (Newton, 1998). In high-latitude regions, weather conditions play a particularly critical role in determining the timing of breeding. Lynch et al. (2009) observed a strong correlation between spring temperature—especially the October average—and the onset of the breeding season. Nevertheless, information on how spring snow conditions affect the breeding biology of Adélie and Gentoo penguins remains limited. Emerging evidence suggests that snow may influence both the timing of breeding and nest-site selection, thereby affecting overall reproductive success (e.g., Lynch et al., 2010; Juáres et al., 2013). Studies have also shown that delayed laying among Adélie penguins correlates with lower breeding success (Hinke et al., 2012; Smiley & Emmerson, 2016; Youngflesh et al., 2017).
Gentoo penguins appear more phenologically flexible, adjusting their laying dates more rapidly than Adélie and Chinstrap penguins (Lynch et al., 2009). In Adélie penguins, the initiation of laying and the degree of laying synchrony are typically high (Ainley, 2002), whereas Gentoo penguins exhibit greater breeding asynchrony, with timing varying across localities and years (Williams, 1981; Bost & Jouventin, 1990b). For Gentoo penguin sites on King George Island, the laying date range spans only about two weeks (Trivelpiece et al., 1987). Seasonal variation in clutch initiation among pygoscelid penguins is largely driven by sea-ice extent and terrestrial snow conditions (e.g., Lynch et al. 2009, Hinke et al. 2012). In our study colony, we observed a similarly strong influence of environmental conditions: in the 2009/10 season, snowmelt delays postponed breeding onset by 14 days in Adélie penguins and 27 days in Gentoo penguins.
Species-Specific Responses to Snow Accumulation
The contrasting breeding seasons of 2008/09, characterized by an early melt and low snow cover, and 2009/10, marked by a delayed thaw and thick snow cover, revealed pronounced differences in how Adélie and Gentoo penguins responded to changing environmental conditions. Snow accumulation in 2009/10 delayed clutch initiation in both species, but Gentoo penguins were disproportionately affected, with higher nest attrition and smaller clutch sizes (Hinke et al., 2012; Lynch et al., 2009). These pressures translated into substantially lower chick survival and breeding success compared to Adélies, which maintained relatively stable outcomes across seasons (Trivelpiece et al., 2011; Cimino et al., 2016).
The greater resilience of Adélie penguins reflects their long evolutionary history in snow- and ice-dominated habitats (Volkman & Trivelpiece, 1981; Ainley et al., 2010). Gentoo penguins, by contrast, are more adaptable foragers at sea (Forcada et al., 2006; Miller et al., 2009) but remain vulnerable to terrestrial constraints such as snow cover. The observed divergence underscores a broader pattern in the Western Antarctic Peninsula: Adélie populations are declining overall but remain better suited to withstand episodic snow events, while Gentoos are expanding poleward yet face acute sensitivity to snow-driven breeding disruption (Meredith & King, 2005; Atkinson et al., 2004).
Nest-Site Selection, Microhabitat Constraints, and Snow Influence
Snow accumulation alters the availability and quality of nesting microhabitats, amplifying these interspecific differences. On Lions Rump, Adélie penguins preferentially occupy elevated ridges and rocky crests that clear of snow earlier in the season (Volkman & Trivelpiece, 1981; Lynch et al., 2010), while Gentoo penguins more often nest in low-lying moraine areas prone to delayed melt and poor drainage (Quintana, 2001; Gwynn, 1953). In 2009/10, these snow-affected sites flooded or remained covered, forcing redistribution of nests and driving much of the reduced reproductive output in Gentoo colonies.
Three mechanisms explain how snow disrupts breeding:
1.
Delayed nest availability — snow cover postpones access to preferred sites, compressing the breeding window (Hinke et al., 2012; Juáres et al., 2013).
2.
Habitat loss and flooding — nests in depressions are lost when snowmelt accumulates (e.g. Hay et al. 2021).
3.
Chick vulnerability — late-hatched chicks face mismatched food availability and higher mortality (Smiley & Emmerson, 2016; Youngflesh et al., 2017).
While both species experience these pressures, Gentoo dependence on snow-prone habitats makes them far more exposed. This explains why snow-heavy seasons, though episodic, play an outsized role in shaping long-term population dynamics (Trivelpiece et al., 2011; Ainley et al., 2010). Occasional years of extreme snow can interrupt or even reverse broader climate-driven trends, making it crucial to understand these events in detail when interpreting population trajectories (Thomas et al., 2008).
Food Availability and Breeding Outcomes
While snow cover clearly emerged as the dominant factor influencing nest attrition and clutch size during the incubation period, food availability likely played a subtler but important role in shaping overall breeding outcomes. Pygoscelis penguins rely heavily on krill (Euphausia superba), and fluctuations in this key resource, driven by oceanographic conditions, can affect reproductive success, particularly during the chick-rearing phase when energetic demands peak (Trivelpiece et al., 1987; Volkman et al., 1981).
At Lions Rump, Adélie penguin fledglings in 2010/2011 were 6.4% lighter than those in 2008/2009, potentially reflecting compounded stress from both snow accumulation and reduced food availability. In contrast, Gentoo penguins at Stranger Point showed no significant interannual variation in fledgling weight over the same period (Juáres et al., 2013), despite experiencing similar snow conditions. This contrast may reflect species-specific sensitivities or differences in foraging success between sites.
The pronounced spatial variation in Gentoo penguin breeding success across Lions Rump, ranging from 1.21 chicks per nest in bedrock areas to just 0.4 in moraine zones, suggests that local microhabitat conditions and snowmelt timing were more immediate and decisive factors influencing egg loss during incubation. Dietary constraints were likely secondary to microhabitat effects, as the 2009/10 diet study from Stranger Point indicated that krill availability was sufficient for chicks across sites, supporting the idea that snow and nest-site exposure were the main drivers of differential breeding success. These observations align with earlier findings on species-specific responses to snow stress and microhabitat constraints (Hinke et al., 2012; Lynch et al., 2009). Although food availability likely influences fledgling condition, the physical nesting environment seems to play a more decisive role in determining overall breeding success than prey abundance alone.
Predation Pressure
Although predation can influence breeding success and nest distribution, its impact at Lions Rump during the study period was minimal. In 2009/2010, the colony of approximately 14,000 penguins was exposed to only nine pairs of avian predators: Brown Skuas (Catharacta antarctica lonnbergi) and South Polar Skuas (C. maccormicki), with just four pairs nesting near the rookery. The largest Adélie penguin nesting site, comprising 3,600–4,000 nests, was dominated by a single skua pair. When skua activity was low, occasional egg predation by Kelp Gulls (Larus dominicanus) was observed, though rarely. Leopard seal (Hydrurga leptonyx) predation was also negligible; in 2008/2009, only one individual was seen hunting penguins near a glacial outflow zone. These observations suggest that predation pressure was low and unlikely to have significantly influenced breeding success during the study seasons.
Conclusion and Future Directions
In conclusion, our findings from the 2009/2010 season on King George Island underscore the significant role of snow cover in shaping nest-site selection, spatial distribution, and breeding success in Gentoo penguins, while Adélie penguins appear less affected. Despite both species achieving similar overall breeding success in the snow-heavy season, Adélie penguins maintained these outcomes with minimal disruption, whereas Gentoo penguins relied on flexible nest-site redistribution to maintain reproductive output. These results suggest that episodic snow accumulation can exert substantial influence on penguin reproductive ecology. Gentoo penguins demonstrated greater phenological flexibility, delaying clutch initiation by up to 27 days, but this did not prevent elevated nest attrition—particularly in poorly drained moraine zones. In contrast, Adélie penguins maintained more stable chick survival and breeding success, suggesting greater resilience to snow-related stress.
Microhabitat characteristics such as elevation, drainage, and pebbles and angular weathered bedrock fragments availability strongly influenced reproductive outcomes, with bedrock and moraine hills offering more favorable conditions than slopes or coastal terraces sites. Our observations suggest that food availability, particularly krill abundance, played a subtler role but was not the primary constraint on breeding success in either Adélie or Gentoo penguins. Predation pressure was minimal during the study period and unlikely to have significantly influenced reproductive outcomes.
To advance understanding of these dynamics, future research should prioritize long-term, multi-site monitoring of snow cover, microhabitat availability, and breeding phenology. Integrating remote sensing, fine-scale habitat mapping, and reproductive metrics across colonies could provide critical insights into species-specific responses to environmental variability. Comparative studies across regions and species will be essential to assess the adaptive limits of phenological flexibility and the role of habitat heterogeneity in buffering climate stress. Such studies would help explain the adaptive capacity and resilience of penguin populations under shifting climatic regimes. Ultimately, integrating behavioral, physiological, and environmental data will be key to predicting how penguin populations respond to ecological change.
A
Acknowledgement
The authors would like to thank Nelson Cho for assistance with statistical analysis. Extended thanks to the captain of Słoń Morski, Tadeusz Cieśluk, for safe journeys during stormy weather on the Bransfield Strait; to all zodiac drivers for safe landings; and to all members of the summer and winter teams of the 33rd and 34th Polish Antarctic Expeditions for their support. The author is also grateful to Anna Angiel and A. Guy Plint for their English revisions of this paper.
Research funding
This research was supported by the Ministry of Scientific Research and Higher Education grant 102/IPY/2007/01 CLICOPEN (ID − 34).
A
Author Contribution
P.J.A. conceptualized the study, developed the methodology, conducted formal analysis, carried out fieldwork, curated and managed data, prepared visualizations, and wrote the original draft. A.G., P.H., E.Ł., K.M., D.R., T.S., and G.W. also carried out fieldwork, curated and managed data, and contributed to writing – review and editing. All authors reviewed and approved the final manuscript.
REFERENCES
AINLEY DG (2002) The Adélie penguin: bellwether of climate change. Columbia University, New York
AINLEY D, JENOUVRIER RUSSELLJ, WOEHLER S, LYVER E, O’B. P, FRASER, W.R., KOOYMAN GL (2010) Antarctic penguin response to habitat change as Earth’s troposphere reaches 2ºC above preindustrial levels. Ecol Monogr 80(1):49–66
AINLEY DG, LERESCHE RE (1973) The Effects of Weather and Ice Conditions on Breeding in Adélie Penguins. Condor 75(2):235–239
ANGIEL PJ, POTOCKI M, BISZCZUK-JAKUBOWSKA J (2010) Characterization of weather conditions at H. Arctowski Station (South Shetland Island, Antarctica) in 2006, in comparison with historical observations. Miscellanea Geogr 14:5–11
ATKINSON A, SIEGEL V, PAKHOMOV, E.A., ROTHERY P (2004) Long-term decline in krill stock and increase in salps within the Southern Ocean. Nature 432:100–103
A
BEWICK V, & LCHEEK BALL J (2004) Statistics review 9: One-way analysis of variance. Crit Care 8(2):130–136BOST CA, JOUVENTIN P (1990a) Evolutionary ecology of Gentoo Penguins (Pygoscelis papua). In: Davis LS, Darby JT (eds) Penguin biology. Academic, London, pp 85–112
BOST C. A. &, JOUVENTIN P (1990b) Laying Asynchrony in Gentoo Penguins on Crozet Islands: Causes and Consequences. Ornis Scand 21(1):63–70
CIMINO MA, MOLINE MA, FRASER WR, PATTERSON-FRASER DL, OLIVER MJ (2016) Climate-driven sympatry may not lead to foraging competition between congeneric top-predators. Sci Rep 6:18820
CROXALL JP, PRINCE PA (1979) Antarctic seabird and seal monitoring studies. Polar Record 19:573–595
FRASER WR, HIEI DJ, TRIVELPIECE WZ (1992) Monitoring Adélie Penguin populations at Palmer Station. Antarct J Unit States 27(5):88–89
FORCADA JPN, TRATHAN K, REID E, MURPHY J, CROXALL JP (2006) Contrasting population changes in sympatric penguin species in association with climate warming. Glob Change Biol 12:411–423
GWYNN AM (1953) The egg-laying and incubation periods of rockhopper, macaroni, and Gentoo penguins. ANARE Rep (Zool) (B) 1:1–29
HAY I, GAYNOR KM, DILLANE SM, STEVENS DJ, AINLEY DG (2021) The influence of subcolony-scale nesting habitat on Adélie penguin colony persistence. Nat Commun 12:4531
HINKE JT, POLITO MJ, REISS CS, TRIVELPIECE SG, TRIVELPIECE WZ (2012) Flexible reproductive timing can buffer reproductive success of Pygoscelis spp. penguins in the Antarctic Peninsula region. Mar Ecol Prog Ser 454:91–104
JUÁRES MA, SANTOS MM, NEGRETE J, SANTOS MR, MENNUCCI JA, ROMBOLÁ E, LONGARZO L, CORIA NR, CARLINI AR (2013) Better late than never? Interannual and seasonal variability in breeding chronology of gentoo penguins at Stranger Point, Antarctica. Polar Res 32:1–11
JUÁRES MA, SANTOS M, MENNUCCI NEGRETEJ, PERCHIVALE JA, CASAUX PJ, R., CORIA NR (2015) Adélie penguin population changes at Stranger Point: 19 years of monitoring. Antarctic Science. 2015;27(5): 455–461
KEJNA M (1999) Air temperature on King George Island, South Shetland Islands, Antarctica. Polish Polar Research 20(3):183–201
KORCZAK-ABSHIRE M, ANGIEL WĘGRZYNM, P.J., LISOWSKA M (2013) Pygoscelid penguins breeding distribution and population trends at Lions Rump rookery, King George Island. Pol Polar Res 34(1):87–99
LYNCH HJ, FAGAN WF, NAVEEN R, TRIVELPIECE SG, TRIVELPIECE WZ (2009) Timing of clutch initiation in Pygoscelis penguins on the Antarctic Peninsula: Towards an improved understanding of off-peak census correction factors. CCAMLR Sci 16:149–165
LYNCH H. J., FAGAN W. F., NAVEEN R., (2010) Population trends and reproductive success at a frequently visited penguin colony on the western Antarctic Peninsula. Polar Biol 33(4): 493–503
MASSOM RA, STAMMERJOHN SE, LEFEBVRE W, HARANGOZO SA, ADAMS N, POOK SCAMBOSTA, M.J., FOWLER C (2006) Extreme anomalous atmospheric circulation in the West Antarctic Peninsula region in Austral spring and summer 2001/02, and its profound impact on sea ice and biota. J Clim 19:3544–3571
MEREDITH MP, KING JC (2005) Rapid climate change in the ocean west of the Antarctic Peninsula during the second half of the 20th century. Geophys Res Lett 32:L19601
MILLER AK, KARNOVSKY NJ, TRIVELPIECE WZ (2009) Flexible foraging strategies of Gentoo penguins Pygoscelis papua over 5Â years in the South Shetland Islands. Antarctica Mar Biology 156(12):2527–2537
NEWTON I (1998) Population limitation in birds. Academic, p 597
PISTORIUS PA, HUIN N, CROFTS S (2010) Population change and resilience in Gentoo Penguins Pygoscelis papua at the Falkland Islands. Mar Ornithol 38:49–53
QUINTANA RD, CIRELLI V (2000) Breeding dynamics of a Gentoo Penguin Pygoscelis papua population at Cierva Point, Antarctic Peninsula. Mar Ornithol 28:29–35
QUINTANA RD (2001) Nest-site characteristics of a Gentoo Penguin Pygoscelis papua colony at Cierva Point, Antarctic Peninsula. Mar Ornithol 29:109–112
RACHLEWICZ G (1997) Mid-winter thawing in the vicinity of Arctowski Station, King George Island. Pol Polar Res 18(1):15–24
REISS CS, COSSIO AM, LOEB V, DEMER DA (2008) Variations in the biomass of Antarctic krill (Euphausia superba) around the South Shetland Islands, 1996–2006. ICES J Mar Sci 65:497–508
ROBERTSON G (1986) Population-Size and Breeding Success of the Gentoo Penguin, Pygoscelis-Papua, at Macquarie Island. Australian Wildl Res 13(4):583–587
A
SCHREIBER AE, Burger (2002) J. CRC, 179–216SMILEY K, EMMERSON LM (2016) A matter of timing: Adélie penguin reproductive success in a seasonally varying environment. Mar Ecol Prog Ser 542:235–249
SMITH RC, STAMMERJOHN SE, BAKER KS, & VERNET M (1999) The Palmer LTER: a case study of a polar ecosystem experiencing climate change. J Antarct Sci 11(3):241–248
STAMMERJOHN SE, MARTINSON DG, SMITH RC, X. YUAN,D. RIND (2008) Trends in Antarctic annual sea ice retreat and advance and their relation to El Niño–Southern Oscillation and Southern Annular Mode variability. J Geophys Research: Oceans, 113(C3), C03S90.
THOMAS DN, WOLFF EW, R. MULVANEY, VAUGHAN DG (2008) A doubling in snow accumulation in the western Antarctic Peninsula since 1850. Geophys Res Lett 35(1):L01501
TRIVELPIECE WZ, TRIVELPIECE SG, VOLKMAN NJ (1987) Ecological Segregation of Adélie, Gentoo, and Chinstrap Penguins at King George Island, Antarctica. Ecology 68(2):351–361
TRIVELPIECE WZ, HINKE JT, MILLER AK, REISS CS, TRIVELPIECE SG, WATTERS GM (2011) Variability in krill biomass links harvesting and climate warming to penguin population changes in Antarctica. Proc Natl Acad Sci USA 108(18):7625–7628
VAUGHAN DG, MARSHALL GJ, CONNOLLEY WM, PARKINSON C, HODGSON MULVANEYR, KING DA, PUDSEY JC, C.J., TURNER J (2003) Recent rapid regional climate warming on the Antarctic Peninsula. Clim Change 60(3):243–274
VOLKMAN NJ, TRIVELPIECE W (1981) Nest site selection among Adélie, chinstrap and Gentoo penguins in mixed species rookeries. Wilson Bull 93:243–248
WIERZBICKI G (2009) Wiatry huraganowe w 2008 roku w Zatoce Admiralicji, Wyspa Króla Jerzego, Antarktyda Zachodnia [Hurricane winds of 2008 in Admiralty Bay, King George Island, West Antarctica]. Sci Rev Eng Environ Sci 44:47–55
WILLIAMS AJ (1981) Factors affecting time of breeding of Gentoo Penguins Pygoscelis papua at Marion Island. In: Cooper, J. (Eds). Proceedings of the Symposium on Birds of the sea and Shore, 1979. Cape Town: African Seabird Group. pp. 451–459
YOUNGFLESH C, JENOUVRIER S, LI Y, JI R, AINLEY DG, BALLARD G, BARBRAUD C, DUGGER DELORDK, EMMERSON KM, FRASER LM, HINKE WR, LYVER JT, OLMASTRONI POB, TRIVELPIECE SSOUTHWELLCJ, TRIVELPIECE SG, W.Z., LYNCH HJ (2017) Circumpolar analysis of the Adélie Penguin reveals the importance of environmental variability in phenological mismatch. Ecology 98:940–951