Justification of Red List Category
The Emperor Penguin is listed as Near Threatened as it is projected to undergo a moderately rapid population decrease as Antarctic sea ice begins to disappear within the next few decades owing to the effects of climate change. By the end of the 20th century, under current levels of CO2 emission more than 80% of the population is projected to be lost, but major changes to sea-ice prevalence are not projected to begin until after 2050. As such, while declines over the next three generations are not expected to exceed thresholds for listing as threatened, future climate scenarios predict a rapid increase in the rate of population decline, such that without mitigation the species will begin to decline rapidly within one to two generations.
A survey of satellite images from 2009, updated in 2019 considered 54 colonies containing approximately 256,500 breeding pairs to be a plausible breeding population estimate (Trathan et al. 2019). The numbers of juveniles, sub-adults and non-breeders are unknown, and the small colonies found since 2014 are not included.
The population trend of the species is predicted to be strongly linked to the condition of ice cover around Antarctica in future. The current population trend is considered stable: from a survey based on satellite images the total population was estimated at 238,000 breeding pairs (Fretwell et al. 2012) while the updated figure for 2019 was 256,500 breeding pairs (Trathan et al. 2019).
However, the future trend is predicted to show an increasingly rapid rate of decline, once changes to the availability of suitable land-fast sea-ice begin to affect breeding success.
In recent decades, there is high confidence that the total Antarctic sea ice cover exhibits no significant trend over the satellite observation era (1979 to 2018; IPCC 2019). The significant positive trend in mean ice cover between 1979 and 2015 has not persisted, following three consecutive years of below-average cover (2016 to 2018; IPCC 2019). The overall Antarctic trend is composed of near-compensating regional changes, with rapid ice loss in the Amundsen and Bellingshausen seas counteracted by rapid ice gain in the Weddell and Ross seas; most of these regional trends are strongly seasonal in character (IPCC 2019).
After the middle of this century, if the current factors leading to Southern Ocean change continue, the annual decrease in net Antarctic sea ice is predicted to reach 48%. A number of Emperor Penguin colonies are then likely to experience complete loss of breeding habitat during the critical egg-laying season (Jenouvrier et al. 2020). Receding sea ice, along with consequent changes in fisheries, are also expected to affect fish and krill stocks (Rintoul et al. 2018), thus threatening the food supply of predators such as Emperor Penguins.
Various analyses and a global demographic assessment of the potential impacts of projected climate change on Emperor Penguins have been carried out (Ainley et al. 2010 and Jenouvrier et al. 2014; 2017, 2020). Under a business-as-usual scenario (RCP 8.5), with unmitigated greenhouse gas emissions throughout the 21st century, Jenouvrier et al. (2019) show that by 2100 all colonies are projected to decrease in size, with 43 of the 54 (80%) colonies projected to decrease by more than 90%, and thus be quasi-extinct. Under this scenario, annual mean Antarctic sea ice extent decreases by 48%, and the breeding habitat of the most endangered colonies, in the north of the range, will probably be lost completely during the critical egg-laying season. Globally, the total abundance of the Emperor Penguins is projected to decrease by 86%, relative to its current size if colonies cannot find more suitable breeding habitat. Simultaneously, the growth rate of the global population is projected to decrease dramatically, resulting in an annual loss of 4.06% per year by the end of this century (a half-life of 17 years). Furthermore, even under a dispersal scenario that leads to the most optimistic population outcome (short distance dispersal, low emigration rate, and informed search), the median of the global population is projected by this model to decrease by 81% (Jenouvrier et al. 2020). Larger decreases are expected under other dispersal scenarios (up to 99% relative to its current size, with long distance dispersal and high emigration rate regardless of dispersal behaviour). By including all uncertainties, the 90% confidence envelope of the global population projections by 2100, range from a decrease of 99.2% to 67% relative to the 2009 initial size. In contrast, if the global temperature rise is kept to 2.0°C, the annual mean sea ice loss is 13% by 2100 (Jenouvrier et al. 2020). As such, only 17 colonies (31%) are likely to be quasi-extinct by 2100, but the global population will decrease by at least 44%.
There are substantial uncertainties over future changes in the patterns of weather variables and how these are likely to impact the species, as well as whether there will be a lag in the decline of mature individuals as recruitment falls, or whether this decline will be proportional to the loss of colonies as climatic changes result in the increased mortality of mature individuals, as with the estimates above. The degree to which the predicted declines will be realised is down to a very large number of variables, but there is a strong indication that if declines are detected in the Emperor Penguin population, they will then be suspected to proceed at an increasingly rapid rate necessitating listing the species at a higher threat category. In the absence of a decline, and noting that the major disruption to ice availability is predicted to begin after the middle of the century, the future rate of population reduction is suspected to be between 20-29% over three generations.
Aptenodytes forsteri has a circumpolar range with approximately 54 breeding colonies located around the entire coast of Antarctica, (Trathan et al. 2019). The largest colonies (> 15,000 breeding pairs) occur in the Ross Sea and Weddell Sea. In recent years, some colonies may have relocated (Ancel et al. 2014, LaRue et al. 2015, Fretwell and Trathan 2019).
Future reduction in the suitable breeding habitat is strongly predicted (Jenouvrier et al. 2020) with major changes predicted from the middle of the current century (Bronselaer et al. 2018). The breeding habitat of Emperor Penguins is discontinuous, and only a seasonal feature. Extent, thickness and duration of sea ice are all changing, with regional differences. Refugia may continue to exist in the higher latitude Weddell Sea and Ross Sea, but the areas suitable as breeding habitat are likely to be only a fraction of those currently available.
Emperor Penguins are high latitude, ice obligate seabirds; they breed throughout the austral winter, are highly cold adapted and spend their entire lives in the Antarctic region, generally in association with sea ice. The vast majority of colonies are dependent upon land-fast sea ice, which they use as breeding habitat, and upon pack ice that they use as foraging habitat.
Information for most colonies is based upon remote sensing, only available recently, as colony access by researchers is limited. Nevertheless, the general life cycle of the species is reasonably well understood, especially for adults at colonies in the north of the species range.
Breeding takes place almost exclusively on coastal land-fast sea ice, sometimes tens of kilometers from ocean access. Only one known colony occurs wholly on land, where the gradation from fast ice to land ice is continuous (Robertson et al. 2014), while a small number uses available land for parts of their breeding cycle. Four colonies are known to locate at least temporarily onto the top of ice shelves (Fretwell et al. 2014).
Emperor Penguins breed throughout the austral winter. They arrive at their colonies in late March to April, and lay eggs in May to June. Chicks hatch after about 65 days and fledge in December to January (Stonehouse 1953; Prévost 1953, 1961). Chicks disperse widely often heading north into waters of the Antarctic Circumpolar Current (Kooyman and Ponganis 2008, Wienecke et al. 2010, Labrousse et al. 2019). Adults moult in summer (January to March) and may travel up to 1200 km to areas of seasonally persistent pack ice, suitable for haul out for several weeks (Kooyman et al. 2004).
Emperor Penguins feed mainly on fish, krill and cephalopods. The relative importance of these dietary items varies with colony location and season (Cherel and Kooyman 1998, Kirkwood and Robertson 1997, Klages 1989, Wienecke and Robertson 1997)
The species is threatened by the effects of projected climate change, primarily through ongoing and future decreases in sea ice concentration, thickness and duration, which are affected by wind speed and persistence, as well as changes in other climatic variables that affect ocean properties (e.g. Ainley et al. 2010; Jenouvrier et al. 2014, 2017, 2020). Global emissions of CO2 from fossil fuels and industry have increased on average by >1.5% per year between 2008 and 2017 (Le Quéré et al. 2018), and by 1.7% in 2018 leading to a concentration of 407.4 ppm in the atmosphere, despite reductions in some developing countries (Le Quéré et al. 2019). Similarly, atmospheric methane has grown very rapidly each year between 2014 and 2017, and the climate warming impact of methane, if continued at >5 ppb per year in the coming decades, will be highly significant (Nisbit et al. 2019).
Most climate models agree that future global climate change will lead to reductions in sea ice area of close to 30% (or 40%) in the latter part of the 21st century following medium (or high) emissions scenarios (Bracegirdle et al. 2008, 2015, Palerme et al. 2017) and therefore will affect Emperor Penguins (Ainley et al. 2010; Jenouvrier et al. 2014, 2017). However, it is important to note that already by mid-century, Emperor Penguins are highly likely to be affected as a destabilization of their breeding platforms prior to fledging, seriously diminishes their chances of breeding successfully.
The decrease of a colony on Emperor Island from c.150 pairs in the 1970s to fewer than 20 pairs by 1999, with the apparent disappearance of the colony by 2009, has been linked to a decrease in seasonally stable sea ice suitable for breeding (Trathan et al. 2011); in the west Antarctic Peninsula region, there has been a statistically significant negative trend in sea ice in March, over the satellite era (IPCC 2019). The colony appears to have moved to a location with more stable ice (LaRue et al. 2015).
In recent years, until 2014, circumpolar Antarctic sea ice had increased in extent. In September 2014, the extent was over 20.11 million km2. Antarctic sea ice extent then rapidly decreased, but since 2016 has increased (IPCC 2019), but remained below the long-term average (see nsidc.org/data/seaice_index; accessed 2 January 2020). Trends in sea ice extent are potentially independent of changes in coastal fast ice: e.g. altered winds may lead to more extensive large-scale sea ice, but possibly reduced fast ice (Ainley et al. 2010). Nevertheless, in the long-term, the loss of large-scale sea ice in general means that ultimately fast ice is also affected. Modelled projections of sea ice remain a key issue, including uncertainty about recent sea ice anomalies. As the Antarctic continues to change, hence so too does Emperor Penguin habitat. In the long term, Emperor Penguin habitat is likely to deteriorate to a point where suitable locations occur only in restricted refugia or, in the worst case scenario, may be completely unavailable (Jenouvrier et al. 2020).
The relocation of Emperor Penguin colonies will be limited by decreases in sea ice thickness and duration, making it more difficult for them to find stable, long-lasting fast ice for breeding (Ainley et al. 2010). Colonies could conceivably move to any area of coastline where breeding habitat remains (e.g. LaRue et al. 2015, Trathan and Fretwell 2019). However, importantly, a simple latitudinal gradient in the loss of sea ice has not occurred and is unlikely in the future (Zwally et al. 2002, Turner et al. 2009, Trathan et al. 2011, Stammerjohn et al. 2012, Fretwell et al. 2012).
Reductions in sea ice concentration and duration reduce the buffering capacity of sea ice to shield fast ice from ocean wave energy (Kim et al. 2018). Such energy can contribute to disintegration of breeding habitat. In addition, basal melting of glacier around the Antarctic continent is increasing, potentially leading to further destabilization of Antarctic sea ice (Bronselaer et al. 2018, Massom et al. 2018, Rignot et al. 2019, Shen et al. 2018). Thus, existing and potential breeding areas of Emperor Penguins are subject to a variety of pressures and much uncertainty.
Out of the water, Emperor Penguins are not agile and cannot easily negotiate rough terrain; they are unable to ascend steep slopes, especially with eggs or small chicks, and require relatively flat, gradual access, either to sea ice, or to beaches (Robertson et al. 2014, Trathan et al. 2019). Loss of suitable breeding habitat is therefore one of the most important challenges that Emperor Penguins face. Recently, breeding on ice shelves has been reported (Fretwell et al. 2014). However, this was only possible where the ablation of shelf fronts or the presence of snow bridges enabled access. Similar opportunities in the future may remain limited, as access varies between years (Zitterbart et al. 2014). In a warming environment potentially causing increased calving of ice shelves, opportunities for this might change. Furthermore, if the rates of flow of ice shelves alter, surfaces may be more highly crevassed. In the long-term, moving onto ice shelves may not be a viable strategy (Fretwell et al. 2014). Ice-free ground is rare in Antarctica (less than 1% of Antarctica; Burton-Johnson et al. 2016) and the probability that suitable rock areas will emerge is difficult to predict.
Another threat to Emperor Penguins is a change in food availability; changes to ocean circulation due to increasing melt of Antarctic ice may interfere with the natural processes that bring nutrients and carbon from the deep ocean back to the surface waters (Lago & England 2019). How this will affect marine organisms, especially those that penguins rely on for food, is as yet unknown. Furthermore, fisheries for Antarctic silverfish Pleuragramma antarcticum, part of the diet of Emperor Penguins, could be developed in the future. Harvesting of silverfish and Antarctic krill Euphausia superba could pose a threat, if management does not adequately take into account the needs of species that feed upon these species. Protection of habitat at sea is important, with the designation of appropriate protection for transit, foraging, moulting and rafting areas at sea.
Human disturbance is a threat in some areas, where problems to colonies are caused by the proximity to scientific bases and aircraft movements (del Hoyo et al. 1992). Sites visited by tourists collectively account for a very small percentage of the global population (J. Croxall in litt. 2017), but the impacts of tourism on breeding penguins remain uncertain (Trathan et al. 2019). Other human impacts potentially include disturbance from researchers, construction of new science facilities and Antarctic krill fisheries. Oil spills may also be important at local scales.
Conservation Actions Underway
The species is the subject of on-going international research. Most on-the-ground studies have been undertaken at colonies in the northern part of the species range. Less is known about the southern colonies in the Ross Sea or Weddell Sea, where the intensity of winter darkness is much greater and it is colder. Pair bonding, breeding, and laying occur later in these high-latitude colonies (G Kooyman in litt. 2019). The natural history beyond post-moult and before return for breeding are unknown and only one study, conducted in the eastern Ross Sea, focused on non-breeders (Goetz et al. 2018).
Human disturbance is regulated in some areas; to date, seven active breeding sites are designated as Antarctic Specially Protected Areas (ASPA), and seven are protected by the Ross Sea Region Marine Protected Area (RSR MPA), of which three are also designated ASPAs. More colonies may eventually become protected. MPAs may afford protection for different life history processes, including potentially breeding, foraging and moulting, as MPAs may provide for more comprehensive protection than do ASPAs. MPAs are essential to protect food resources while ASPAs only protect breeding areas: the RSR MPA will protect over 1.5 million km2 of the Southern Ocean from commercial fishing over the next 35 years (Australian Birdlife 2016).
Currently however, the RSR MPA protects only one of the Emperor Penguin meta-populations proposed by Younger et al. (2015, 2017). Protection of more genetically distinct meta-populations might be important for future resilience to environmental change.
Conservation Actions Proposed
Conduct regular satellite surveys to monitor population trends in the context of habitat availability (e.g. Fretwell et al. 2012, LaRue et al. 2015). Continue monitoring at the individual level and ground-based monitoring of some colonies located along a latitudinal gradient to estimate demographic parameters and their responses to environmental change (e.g. Barbraud and Weimerskirch 2001, Ancel et al. 2014, Jenouvrier et al. 2014, Robertson et al. 2014, Kooyman and Ponganis 2016). Continue to improve on existing modelling work to improve predictions of future population changes (see Jenouvrier et al. 2019). Carry out further research into the species' marine ecology (e.g. age-specific migration routes/distances and foraging strategies) and meta-population structure (e.g. Cristofari et al. 2016; Younger et al. 2015, 2017) to improve understanding of how environmental changes will affect the population. Continue to monitor Antarctic sea ice as well as other environmental variables and processes to assess the availability of suitable breeding habitat and foraging grounds. Continue international work to provide protection.
The archetypal Antarctic penguin, huddling out the long freezing dark of the longest winter and emerging into spring with chicks. Much larger and heavier than King Penguin, and capable of even more astonishing aquatic feats. A source of fascination and admiration in humans since the first exploration of the ice continent, and supporting cast to the most extreme feats of human endeavour. A fundamental element of the human relationship with Antarctica.
Text account compilers
Martin, R., Trathan, P. N., Westrip, J.R.S., Wienecke, B., Everest, J., Moreno, R., Pearmain, L.
Ainley, D., Ancel, A., Ballard, G., Barbraud, C., Clucas, G., Cristofari, R., DuBois, L., Fretwell, P., García Borboroglu, P., Jenouvrier, S., Kooyman, G., LaRue, M., Le Bohec, C., Makhado, A., Schmidt, A., Schneider, T., Trathan, P. N., Wienecke, B., Woehler, E., Younger, J. & Zitterbart, D.
BirdLife International (2021) Species factsheet: Aptenodytes forsteri. Downloaded from http://www.birdlife.org on 04/03/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 04/03/2021.