The explorer king: southern report of the king penguin (Aptenodytes patagonicus) in the Antarctic Peninsula

Abstract

A juvenile king penguin (Aptenodytes patagonicus) was sighted at San Martín Station, Marguerite Bay, west of the Antarctic Peninsula (68°07'S, 67°08'W) on 3 February 2020. The animal was apparently healthy. It was uninjured, moving freely between the station buildings. It remained in the area until 27 March, when it was last seen. Numerous king penguin records have been reported in recent years, mostly in the South Shetland Islands. Two chicks have even been recorded hatching on these islands, but there is currently no evidence that king penguins have raised a chick to emancipation successfully. Here we present the most southerly known record of king penguins, the only one farther south than the Antarctic Circle. Coupled with observations from other parts of Antarctica, the information presented here supports previous suggestions by other authors of a southwards expansion of this species specifically in the Antarctic Peninsula region. The presence of this species at numerous Antarctic localities suggests that the known distribution of this penguin could change in the near future in response to climate change.

Introduction

The king penguin (Aptenodytes patagonicus; hereinafter KP) is a pelagic species with circumpolar distribution and with reproductive colonies on the sub-Antarctic islands between parallels 45° and 55°S (Bost et al. 2013, Pütz et al. 2014). The largest population of KPs in the south-west Atlantic sector is found on the South Georgia Islands, which are the southernmost breeding colonies (Bost et al. 2013). Vagrant individuals have been reported in southern latitudes such as Laurie Island in the South Orkney Islands, Elephant Island and King George Island (25 de Mayo Island) in the South Shetland Islands and Neko Harbour on the Antarctic Peninsula (Coria et al. 2011, Bost et al. 2013, Petry et al. 2013, Juáres et al. 2014, Borowicz et al. 2020). Regardless of the breeding site, in summer the reproductive adults feed on or close to the Antarctic polar front (Scheffer et al. 2012), and in autumn/winter they make long trips to the marginal ice zone, where the availability of prey is higher (Pütz et al. 2014). Recently, breeding and hatching attempts have been reported south of their historical range, suggesting expansion of their latitudinal limits (Petry et al. 2013, Juáres et al. 2014, Borowicz et al. 2020).

At the beginning of the century, the global population of KPs decreased as a result of anthropogenic actions. Currently, the largest KP populations are located on the Crozet Islands, the Kerguelen Islands, the South Georgia Islands, Heard Island and Macquarie Island (Bost et al. 2013). KPs have returned to former areas of presence, such as in the Malvinas Islands/Falkland Islands and Heard Island (Pistorius et al. 2012). This recovery translates into competitive pressure for space; the increase in population density and the greater proximity to the coast caused the displacement of pairs to the periphery of the colonies, with consequent increases in their latitudinal extensions of distribution (Chamaillé-Jammes et al. 2000).

The number of breeding pairs observed on the Antarctic Peninsula, particularly on Elephant Island and the South Shetland Islands, is part of a phenomenon to be analysed, as we are not yet sure what environmental factors constrain KP breeding (Petry et al. 2013, Juáres et al. 2014, 2017, Borowicz et al. 2020).

San Martín Station (68°07'S, 67°08'W) is located in the west of the Antarctic Peninsula (WAP) and could represent a potential habitat for KPs in the immediate future. Following Cristofari et al. (2018), San Martín Station has appropriate conditions for colonization: 1) free of ice and reasonably flat, 2) with sites within the maximum feeding distance and 3) low concentrations of sea ice during winter. Our objective is to document the southernmost occurrence record reported to date for the KP species. The high dispersal capacity of KPs, together with the observed trends of some environmental variables in the WAP, imply that southern locations such as San Martín Station could be suitable for the presence of this species in the future.

Observations

Study area

San Martín Station is located on Barry Islet, Marguerite Bay, WAP (68°07'S, 67°08'W; Fig. 1). The annual average maximum temperature is -1.5°C and the annual average minimum temperature is -8.5°C. The average annual wind intensity is 17.6 km/h, reaching gusts of more than 200 km/h. The islet is ~350 m long and ~230 m wide.

Figure 1. Location of the study area (upper left map), Marguerite Bay, west of the Antarctic Peninsula (lower left map) and San Martín Station, Barry Islet, Antarctica (right picture by Gastón Jacob).

King penguin sighting

On 3 February 2021, the station's scientific staff recorded the appearance of a KP specimen on Barry Islet. It was an immature individual, with dull and brown head and dorsal areas, a dull upper breast and a slightly dull bill stripe (Fig. 2). The plumage colour patterns suggest that it was a 1 or 2 year-old individual as from the third year KPs acquired their adult plumage.

Figure 2. King penguin (Aptenodytes patagonicus) juvenile at San Martín Station during summer 2021. a. General appearance; b. detail of head; c. close-up of the head, neck and chest. Photographs taken by Leandro Nahuel Solis Etchegoin and Rodrigo Azpilcueta.

The animal was apparently in good health. It had no injuries, moved freely and was very curious and sociable with humans. At times it was not in sight, suggesting that it was probably on feeding trips in the area. The penguin stayed on Barry Islet and was last seen on 27 March.

Discussion

Our work reports a KP sighting at the southernmost point of the distribution limits of the species. Its presence could be coupled to processes derived from population growth and from adaptive responses to climate change, resulting in increases in the environmental and trophic niches of the species. It was suggested that the arrival of the KP specimens reported at Stranger Point, South Shetland Islands, may have originated from the colonies of the South Georgia Islands (Juáres et al. 2014). This implies a linear route of ~1,500 km. However, in the case of the San Martín Station KP, its immigration could have started in the South Shetland Islands (King George/25 de Mayo Island or Elephant Island), where breeding events and population growth have been recorded (Petry et al. 2013, Juáres et al. 2017, Gryz et al. 2019, Borowicz et al. 2020). This specimen was recorded from February to March.

The KP record at the San Martín Station could suggest the expansion of the reproduction range of this species, however, the reasons for the presence of KPs in the Antarctic region continue to be speculative. Foraging site fidelity allows KPs to exploit areas with available and predictable prey; therefore, South Shetland Islands-recorded adults probably forage in Antarctic Polar Front waters or even further south (Scheffer et al. 2012, Petry et al. 2013). The frequency of observations outside the southern limits of KPs are increasing; these isolated immigration processes could favour population growth and the expansion of future environmental and trophic niches (Petry et al. 2013, Juáres et al. 2017, Borowicz et al. 2020).

The Antarctic Peninsula region, particularly WAP, is warming faster than any other region in the Southern Hemisphere, and the Antarctic Polar Front is predicted to double its southwards shift by 2100 (Péron et al. 2012). Faced with scenarios of environmental and physical variability, penguin species have responded by changing their distribution patterns and breeding ranges considerably (Gorman et al. 2010). KPs could show us the effects of climate change directly through its impacts on the environmental tolerance thresholds of the species and indirectly through the expanding population densities and trophic resources for the species. In this sense, there is limited knowledge regarding the adaptive responses of KPs to new environmental scenarios derived from climate change (Petry et al. 2013). Because the effects of climate change are cumulative, wildlife will experience these impacts over several generations. Due to the scarce information available, it is the responsibility of scientists to record these events in order to allow effective and consistent responses to present and future environmental scenarios.