Climate Change Coastal Management Conservation Ecology Fisheries Human impacts Modeling Natural History Sea Ice

Warming up to the neighborhood: a gentoo penguin’s new digs

Citation: Korczak-Abshire, M., Hinke, J. T., Milinevsky, G., Juáres, M. A. and Watters, G. M. 2021. Coastal regions of the northern Antarctic Peninsula are key for gentoo populations. Biol. Lett. 17:20200708.http://doi.org/10.1098/rsbl.2020.0708

A lone gentoo penguin on a walk. commons.wikimedia.org

When you hear the word “Antarctica,” things such as glaciers, brutal winds, and penguins likely come to mind. Combine that with “climate change” and you might think of melting ice sheets and habitat loss for said penguins. That might be the case for ice-reliant species like the Adélie or Emperor penguin, but for the ice-intolerant gentoo (pronounced JEN-too) penguin, the shift in temperatures is an invitation to expand their range as more coastal areas along the Antarctic Peninsula are exposed for longer throughout the year. Gentoo penguins prefer low, ice-free elevations for their breeding colonies since the birds build their nests from collected pebbles. This preference has led to two the formation of two subspecies, with one population colonizing island chains north of the Polar Front surrounding Antarctica, and the other limited to a few islands along the western Antarctic Peninsula. (Fig. 1)

Figure 1: Habitat range of gentoo penguins. The orange region shows the approximate area gentoo penguins are typically found. They inhabit island chains north and south of a sea-ice belt that effectively divides their species into two subspecies.

Conditions around the western Antarctic Peninsula have been changing rapidly in recent decades, but data on how this has been affecting local organisms has trickled in at a slow pace. So, an international team of researchers addressed this gap in information by documenting the movements of 75 gentoo penguins over the course of a year in an effort to see how they are responding to the altered environment and assessing if there are other stressors impacting the population.

Researchers anticipated gentoos would travel shorter distances throughout the breeding season (November through January), as most would need to return to shore to care for chicks. Outside of the breeding season, they expected some southern colonies to expand further south, with the development and presence of sea ice acting as a type of barrier for the gentoos. What these satellite-tracked birds showed, however, did not match expectations.

Penguins from five separate groups, including individuals from one of the most recently established, southern colonies, were captured and tagged with satellite tags. Most tags transmitted data for a period of 4-10 months (from February through October), sending regular signals during the penguins’ typical hunting time. Researchers stitched the tracks together and created an estimated map of each colony’s range based on a penguin’s average swim speed.

While the penguins limited their travel as the breeding season approached, individuals from the separate colonies expanded their ranges further southwest along the peninsula during non-breeding months. (Fig. 2) Thanks to how specific the trackers were, researchers observed northern gentoo penguin individuals swimming further than their southern colony cousins. This kind of leap-frogging strategy has been seen before in other birds, but hasn’t been documented in gentoos before.

Figure 2: Model-predicted range of five colonies. Penguins tagged from five colonies were tracked over a number of months. Ranges were estimated based on swim speed and location data, and shown as clusters of hexagons. Key: Argentine Islands (dark blue), Cierva Cove (purple), Cape Shirreff (light blue), Stranger Point (orange) and Lions Rump (yellow). Korczak-Abshire et al., (2021) Figure 2.

As for the sea ice? Only dense sea ice formation (where more than 50% of the ocean’s surface was covered) kept gentoos from pushing further south. If sea-ice formed over less than 50% of water, the penguins were still able to set up shop and forage for food along the peninsula’s shelf. Should sea ice continue to decline in those regions throughout the next century, these gentoo colonies will likely continue expanding their ranges.

Since the ice, surprisingly, isn’t as much a deterrent as expected, the main concern for the future homes of gentoo penguins will be prey availability. The western Antarctic Peninsula is generally ripe with krill—a favorite gentoo food, and a species that supports a growing fishery. The gentoos’ health will be directly linked to how well (and how much of) the krill survives under pressure by fisheries and other predators. As with most things, the team acknowledged the data is lacking. This study, though, points us in a good direction so we can better understand this species’ changing future.

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