Glacier retreat caused by anthropogenic climate change is often in the news because of its impacts on sea level rise and shrinking habitats. However, a recent study published by Lee et al. in the Journal of Ethology has found that glacier retreat on King George Island could have a positive impact on kelp gulls, exposing new ground with suitable breeding sites.
The kelp gull, Larus dominicanus, breeds on coasts and islands throughout the Southern Hemisphere, as detailed on the IUCN Red List. It has a large range, from subantarctic islands and the Antarctic peninsula to coastal areas of Australia, Africa and South America. Breeding occurs between September and January, with nests usually built on bare soil, rocks or mud in well-vegetated sites.
King George Island, the largest of the South Shetland islands, is part of the kelp gull’s range. It can be found off the coast of the Antarctic peninsula and is a nesting ground for seabird species during the summer months. Numerous research stations are located on the island, and its coasts are home to a variety of wildlife, such as elephant and leopard seals, and Adelie and Gentoo penguins.
Research has shown that breeding nests of kelp gulls have been recorded in ice-free areas of King George Island since the 1970s. Studies of Gentoo penguin populations also suggest that rapid glacier retreat could give species that favor ice-free environments a chance to expand their habitats. As such, Lee et al. used a combination of satellite photographs and field observations of kelp gull nests in newly exposed locations to study possible correlations between glacier retreat and nest distribution in the Barton Peninsula on King George Island.
Based on eight different satellite images, Lee et al. determined that glaciers on the Barton Peninsula have retreated 200-300m from the coast since 1989, exposing an area of approximately 96,000 square kilometers. Within this area, they found up to 34 kelp gull breeding nests between 2012 and 2016, along with evidence that kelp gulls have been breeding on newly exposed ground for decades.
As the glaciers on the Barton peninsula retreat inland, moraine surfaces made up of glacial soil and rock debris are left on the coast. Rocks within these moraines provide shelter from harsh Antarctic coastal winds, reducing the stress to the gulls arising from these winds. This makes the exposed areas more attractive for breeding.
Previous studies have suggested that kelp gulls select nest sites in favorable locations with rock and vegetation cover, and kelp gull populations are known to nest in neighboring areas like Potter Peninsula and Admiralty Bay. In this study, kelp gull nests were found between 40-50cm away from the rocks, suggesting that a combination of rocks and vegetation present on the moraines help to create favorable nesting conditions.
These gulls probably originated from neighboring kelp gull populations, such as those on King George Island or the Nelson Islands. Continued retreat of glaciers on King George Island could expose larger areas of suitable breeding ground, attracting more gulls from neighboring islands and increasing kelp gull populations.
Anthropogenic climate change and glacier retreat have many adverse effects, but research like this sheds light on the ways in which some species might benefit in unexpected ways.