This discussion was first published as part of the 2010-2011 Red List update.
Initial deadline for comments: 31 January 2012.
Emperor Penguin Aptenodytes forsteri and Adelie Penguin Pygoscelis adeliae are both currently listed as Least Concern on the basis that they were not believed to approach the thresholds for Vulnerable under any of the IUCN criteria. Both species have large ranges, and hence do not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence less than 20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Their population trends appear to be stable or perhaps decreasing slightly overall, and hence these species do not approach the thresholds for Vulnerable under the population trend criterion (at least a 30% decline over ten years or three generations). Their populations are very large, and hence do not approach the thresholds for Vulnerable under the population size criterion (fewer than 10,000 mature individuals with a continuing decline estimated to be at least 10% over ten years or three generations, or with a specified population structure).
In a recent paper by Ainley et al. (2010), these two species are predicted to decline in the northern part of their respective ranges during the next 15-42 years owing to projected changes in sea ice and precipitation. In this paper a set of climate models used in the IPCC Fourth Assessment Report (AR4) was tested to find those that most closely predicted data collected on environmental conditions in the Southern Ocean over recent decades. The four best performing models were found to estimate the point at which the average tropospheric temperature reaches 2°C above pre-industrial levels to occur in the period 2025-2052. An ensemble of models was then used to predict changes in climate and habitat in the Southern Ocean until 2025-2052, namely sea ice extent, persistence, concentration and thickness, wind speeds, precipitation and air temperature. Following this, qualitative predictions were made of changes to the populations of pack ice penguins, A. forsteri and P. adeliae, based on historic responses of the species to past variation in environmental conditions. Using this methodology it is predicted that all colonies north of 67°S will be lost, and that all colonies north of 70°S will experience some negative effects, owing primarily to decreases in sea ice concentration and thickness (Ainley et al. 2010). Such predictions, at least for the Emperor Penguin, are consistent with the quantitative modelling carried out by Jenouvrier et al. (2009), although the latter authors used climate models that made projections until 2100. However, there is considerable uncertainty; for example an overall decline in sea ice extent could be accompanied by positive trends in some areas. Over recent decades (1979-2007), the trend in sea ice extent has actually been positive overall, with negative trends in the Antarctic Peninsula area (Turner et al. 2009); this pattern is associated with stronger winds, which are probably linked to the hole in the ozone layer (Thompson and Solomon 2002, Turner et al. 2009) and to the warming of mid-latitudes (Russell et al. 2006), but could also be within the bounds of natural climate variability (Stammerjohn et al. 2008, Turner et al. 2009). However, AR4 models that reproduce changes observed since 1951 forecast a 24% reduction in mean annual sea ice extent in the Antarctic by 2100 (Arzel et al. 2006).
Calculating the rate of population decline that could result from such changes is further hindered by uncertainty over population estimates. As pointed out by Wienecke (2010) for A. forsteri, the estimated population size for these species is the product of many surveys that have taken place in different years and at different stages in the annual cycle and have employed various methods and standards of accuracy, owing largely to the logistical constraints posed by the Antarctic environment. However, Wienecke’s (2009, 2010) call for A. forsteri to be listed as Data Deficient under the IUCN criteria is perhaps overly pessimistic, not accounting for the importance of using admittedly imperfect data to apply the precautionary principle, and not recognising that it may be adequate to express uncertainty in population estimates. Fretwell and Trathan (2009) provide an up-to-date review of the locations of A. forsteri colonies, as carried out through the surveying of satellite images; however, there is still considerable uncertainty over the total population size and current trend. For the purposes of assessing the potential impact of the changes predicted by Ainley et al. (2010), estimates of the total number of breeding pairs for these species have been calculated from published survey results, with upper and lower estimates calculated based on the accuracy coding put forward by Croxall and Kirkwood (1979). It should be noted that there are unexplained discrepancies between the population estimates calculated here and those given by Ainley et al. (2010), despite the use of the same data in each case. Also note that in this forum topic, an attempt has not been made to discuss all of the factors that might affect these two species in what is a complex set of predictions made by Ainley et al. (2010); however, those judged to most important are outlined here.
Emperor Penguin (A. forsteri)
Population trend projections over three generations (61 years; trend period 2010-2071), assuming an exponential decline, have been carried out for this species based on the predictions made by Ainley et al. (2010) and the most recent survey results available, as collated and published by Woehler (1993), Woehler and Croxall (1997), Splettstoesser et al. (2000), Todd et al. (2004) and Lea and Soper (2005). The total population size is estimated to be 212,000 pairs (range 162,000-302,000 pairs). The number of pairs in colonies north of 67°S is estimated to be 53,900 (range 33,900-116,000); the rate of decline has been projected assuming the loss of these colonies and using actual survey results, thus the inaccuracy of survey methods has not been factored into the trend projections. The relocation of A. forsteri colonies will be limited by decreases in sea ice thickness, making it more difficult for them to find stable, long-lasting fast ice for breeding. Colonies could conceivably move to any areas of coastline not affected by ridges formed by wind-blown pack ice; however, where this has occurred in the past it has been regarded as a rare event.
A mid-range trend projection was made based on a time scale of 2010-2042, with 2042 being the average year at which a 2°C warming is forecast to be exceeded by the four models used by Ainley et al. (2010). Projections were also made based on the loss of the same northern colonies over two extreme time scales of 2010-2025 and 2010-2052. The mid-range calculation projects a decline of 43% over 61 years, with extreme lower and upper projections coming in at declines of 35% and 70% respectively. In a separate analysis using forecasts from 10 IPCC models whose predictions matched satellite data on sea ice extent, Jenouvrier et al. (2009) predict a decline in population viability of the Terre Adelie colony (c.66°S) with increasing frequency of warm events, which are defined by reduced sea ice extent. A projected decline in the median population size of c.6,000 pairs in 2006 to c.400 pairs by 2100 is equivalent to an 83% decline over three generations (2006-2067). Indeed, stochastic population projections suggest that the chance of a population decline of 95% or more (quasi-extinction) by 2100 is 36-84% according to the range of predicted frequencies of warm events, as defined by different thresholds for sea ice extent. These projections for the Terre Adelie colony may actually be conservative, as in this study future warm events were assumed to have the same impact as the warm events of the 1970s, whereas IPCC models predict them to get warmer (Jenouvrier et al. 2009).
Based on the projections made by Ainley et al. (2010), and factoring in a degree of uncertainty over the ability of the species to adapt to the expected alterations to its environment, it is proposed that it be uplisted to Vulnerable under criterion A3c, on the basis that a decline of 30-49% is projected to occur over three generations owing to declines in the Area of Occupancy, Extent of Occurrence, and/or quality of habitat. Comments on this proposed category change would be welcomed.
Adelie Penguin (P. adeliae)
Population trend projections over three generations (36 years; trend period 2010-2046), assuming an exponential decline, have also been carried out for P. adeliae based on the predictions made by Ainley et al. (2010). The total number of breeding pairs is estimated to be 2.37 million (range 1.83-2.88 million), based on survey data collated and published by Woehler (1993) and Woehler and Croxall (1997). According to the same data, the number of pairs situated in colonies north of 67°S is estimated to be 926,000 (range 595,000-1,270,000). As with A. forsteri, a mid-range trend projection was made based on the loss of colonies north of 67°S over a time scale of 2010-2042, and projections were also made based on the same changes taking place over two extreme time scales of 2010-2025 and 2010-2052. As for A. forsteri, the mid-range calculation projects a decline of 43% over 36 years, with extreme lower and upper projections also coming in at declines of 35% and 70% respectively. In this species, some relocation of colonies is expected, with limited growth perhaps occurring south of 73°S (Ainley et al. 2010). The species would be expected to colonise new areas as the collapse of ice shelves at northern latitudes exposes new areas of coastline, and as highly concentrated sea ice at southern latitudes becomes more divergent. Reduced suitability of nesting habitat and increased mortality, however, could result from an increase in the incidence of severe snowfall. In addition, annual migration and winter survival may be negatively affected by decreases in sea ice coverage at northern latitudes where the species requires a few hours of daylight in each 24-hour period (Ainley et al. 2010, Ballard et al. 2010). With these factors in mind, it is proposed that the species be uplisted to Near Threatened under criterion A3c, on the basis of a lower projected decline of 10-29% over 36 years, owing to decreases in the Area of Occupancy, Extent of Occurrence, and/or quality of habitat. Comments on this proposed category change would be welcomed.
Ainley, D., Russell, J., Jenouvrier, S., Woehler, E., Lyver, P. O’B., Fraser, W. R. and Kooyman, G. L. (2010) Antarctic penguin response to habitat change as Earth’s troposphere reaches 2°C above preindustrial levels. Ecol. Monogr. 80: 49-66.
Arzel, O., Fichefet, T. and Goosse, H. (2006) Sea ice evolution over the 20th and 21st centuries as simulated by current AOGCMs. Ocean Modell. 12: 401-415.
Ballard G., Toniolo, V., Ainley, D. G., Parkinson, C. L., Arrigo, K. R. and Trathan, P. N. (2010) Responding to climate change: Adélie penguins confront astronomical and ocean boundaries. Ecology 91: 2056-2069.
Croxall, J. P. and Kirkwood, E. D. (1979) The Distribution of Penguins on the Antarctic Peninsular and Islands of the Scotia Sea. Cambridge, UK: British Antarctic Survey.
Fretwell, P. T. and Trathan, P. N. (2009) Penguins from space: faecal stains reveal the location of emperor penguin colonies. Global Ecol. Biogeogr. 18: 543-552.
Jenouvrier, S., Caswell, H., Barbraud, C., Holland, M., Strœve, J. and Weimerskirch, H. (2009) Demographic models and IPCC climate projections predict the decline of an emperor penguin population. P. Natl. Acad. Sci. USA 106: 1844-1847.
Lea, M.-A. and Soper, T. (2005) Discovery of the first Emperor Penguin Aptenodytes forsteri colony in Marie Byrd Land, Antarctica. Mar. Ornithol. 33: 59-60.
Russell, J. L., Dixon, K. W., Gnanadesikan, A., Stouffer, R. J. and Toggweiler, J. R. (2006) The Southern Hemisphere Westerlies in a Warming World: Propping Open the Door to the Deep Ocean. J. Climate 19: 6382–6390.
Splettstoesser, J. F., Gavrilo, M., Field, C., Field, C., Harrison, P., Messick, M., Oxford, P. and Todd, F. S. (2000) Notes on Antarctic wildlife: Ross seals Ommatophoca rossii and emperor penguins Aptenodytes forsteri. New Zeal. J. Zool. 27: 137-142.
Stammerjohn, S. E., Martinson, D. G., Smith, R. C., Yuan, X. and Rind, D. (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. Res. 113: C03S90.
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Todd, F. S., Adie, S. and Splettstoesser, J. F. (2004) First ground visit to the emperor penguin Aptenodytes forsteri colony at Snow Hill Island, Weddell Sea, Antarctica. Mar. Ornithol. 32: 193-194.
Turner, J., Comiso, J. C., Marshall, G. J., Lachlan-Cope, T. A., Bracegirdle, T., Maksym, T., Meredith, M. P. Wang, Z. and Orr, A. (2009) Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent. Geophys. Res. Lett. 36: L08502.
Wienecke, B. (2009) Emperor penguin colonies in the Australian Antarctic Territory: how many are there? Polar Record 45: 304-312.
Wienecke, B. (2010) Review of historical population information of emperor penguins. Polar Biol. Published online: 8 October 2010: http://www.springerlink.com/content/h1r27531l858gx84/. Accessed on 8 November 2010.
Woehler, E. J. (1993) The Distribution and Abundance of Antarctic and Subantarctic Penguins. Cambridge, UK: Scientific Committee on Antarctic Research.
Woehler, E. J. and Croxall, J. P. (1997) The status and trends of Antarctic and sub-Antarctic seabirds. Mar. Ornithol. 25: 43-66.
Since this topic was written and posted, Phil Trathan has brought to our attention that the following relevant paper has been published:
Trathan, P. N., Fretwell, P. T. and Stonehouse, B. (2011) First Recorded Loss of an Emperor Penguin Colony in the Recent Period of Antarctic Regional Warming: Implications for Other Colonies. PLoS ONE 6(20): e14738. doi:10.1371/journal.pone.0014738 (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0014738).