Introduction
King penguin (Aptenodytes patagonicus Miller; hereafter KP) is a circumpolar species that breeds on sub-Antarctic islands, between 45° and 55°S. Although vagrant individuals can be found in the Antarctic region (south of 60°), these sites are not included in the historic breeding range of the species (Williams Reference Williams1995). However, Petry et al. (Reference Petry, Basler, Valls and Krüger2013) reported a possible recent southward expansion of the KP breeding range. These authors consider that an increment in the number of breeding pairs observed on Elephant Island, South Shetland Islands (SSI) could occur as a consequence of global warming.
In the Antarctic marine ecosystem, where a substantial environmental variability has been demonstrated in the global climate change context (Ducklow et al. Reference Ducklow, Baker, Martinson, Quetin, Ross, Smith, Stammerjohn, Vernet and Fraser2007), shifts in distribution and breeding range of species are one of the main ecological responses (Gorman et al. Reference Gorman, Erdmann, Pickering, Horne, Blum, Lucas, Patterson-Fraser and Fraser2010, McClintock et al. Reference McClintock, Silva-Rodriguez and Fraser2010). In this paper, we report the southernmost breeding attempt of a KP pair incubating at King George Island (Isla 25 de Mayo), SSI. Our observations contribute further evidence to reinforce the Petry et al. (Reference Petry, Basler, Valls and Krüger2013) hypothesis.
Observations
Stranger Point (62°15′S, 58°37′W) is an Antarctic location situated on King George Island (Isla 25 de Mayo), SSI (Fig. 1a). At this site, Adélie (Pygoscelis adeliae [Hombron & Jacquinot]) and gentoo penguins (P. papua Forster) nest sympatrically. During the 2010–11 breeding season, one KP was registered for few days at the study area. The following season, on 21 December 2011, a KP pair was observed breeding in a gentoo penguin's nesting site, about 200 m off the coastline (Fig. 1b). An egg was recorded for the first time on 4 January 2012 but it was abandoned on 2 February 2012 before hatching. During the 2012–13 season (21 October 2012), one KP remained at the colony during pre-nuptial moult fasting for at least 16 days. Later on that season, on 3 December 2012, a pair of KPs were observed and the courtship started the next day. On this occasion an egg was registered on 13 December, the incubation occurred associated to a mixed breeding group (Adélie and gentoo penguins, Fig. 1c) closer to the coastline (70 m). On 8 January 2013 neither the adult nor the egg were registered following two days of a snowstorm.
King penguin southernmost record. a. Study area. Stranger Point, King George Island (Isla 25 de Mayo), South Shetland Islands. b. Breeding couple observed during 2011–12 season. c. Reproductive pair registered in 2012–13 season. Photographs taken by Lucrecia Longarzo and Pablo J. Perchivale.
Discussion
An expansion of breeding range normally coincides with a population increase and gain of new available sites for nesting (McClintock et al. Reference McClintock, Silva-Rodriguez and Fraser2010). Between the 1960s and 1990s, KP populations recovered from an over-exploitation episode, increasing the number of breeding couples (see Delord et al. Reference Delord, Barbraud and Weimerskirch2004). Nevertheless, a decrease in population growth rate was recorded for some colonies which have reached carrying capacity (Delord et al. Reference Delord, Barbraud and Weimerskirch2004). King George Island is situated at c. 1500 km from South Georgia, where the largest Atlantic Ocean population of KP is found (Poncet Reference Poncet2006). Given the relevance of immigration in population growth and formation of new colonies (Delord et al. Reference Delord, Barbraud and Weimerskirch2004), we consider that the KP recorded at Stranger Point possibly came from the South Georgia rookery, for which a population increment was recently report (Poncet Reference Poncet2006).
The occurrence of KP individuals and/or breeding pairs recorded at the SSI, south of the historic range, suggests an incipient expansion of the species’ distribution. Probable causes for this event include: 1) the emergence of new suitable breeding areas, as a consequence of environmental change, and 2) density-dependent factors, as a result of the population's increase some individuals may mobilize in search of new breeding sites, possibly the youngest ones that have a higher migration rate (Williams Reference Williams1995).
The first breeding site south of the KPs’ reproductive range was reported by Petry et al. (Reference Petry, Basler, Valls and Krüger2013), located at Elephant Island, SSI, which is situated c. 212 km north-east of Stranger Point (Fig. 1a). Our records represent the southernmost breeding attempts reported so far and the presence of nesting pairs during several seasons could indicate the emerging consolidation of a future breeding colony (Gorman et al. Reference Gorman, Erdmann, Pickering, Horne, Blum, Lucas, Patterson-Fraser and Fraser2010). However, for this to occur the number of breeding pairs would have to increase in order to favour the survival of the offspring, as stated by Petry et al. (Reference Petry, Basler, Valls and Krüger2013), given that the crèche is important for chicks’ protection against adult aggression, predation and the weather (Le Bohec et al. Reference Le Bohec, Gauthier-Clerc and Le Maho2005). For this reason, despite the fact that local conditions at Stranger Point were favourable for egg laying, it is highly probable that, even if the egg had hatched, the chick would not have survived the winter season.
Although we agree with Petry et al. (Reference Petry, Basler, Valls and Krüger2013) that the explanations for the presence of these birds in the Antarctic region are speculative, we consider that this new and southernmost record of breeding attempts help to reinforce the conclusions of those authors. It cannot be dismissed that the presence of these individuals could be a result of an inexperienced breeding pair; however, reports of reproductive specimens in the area seem to be increasing. As there is insufficient evidence to recognize the causal mechanisms, it is essential to continue observing and distributing these kinds of events. Moreover, as was proposed by Gorman et al. (Reference Gorman, Erdmann, Pickering, Horne, Blum, Lucas, Patterson-Fraser and Fraser2010), this type of report also helps to better understand species’ life history strategies.
Acknowledgements
We want to thank Lucrecia Longarzo, Guillermo Panisse, Miguel Gasco, Patricia Pastorizo, Ariel Pereira and the mammals group for field assistance. To Florencia Matus for her help. The Instituto Antártico Argentino provided financial and logistical support. We thank the two anonymous reviewers and Professor Walton for their comments on the manuscript.
