Skua and plant dispersal: Lessons from the Argentine Islands - Kyiv Peninsula region in the maritime Antarctic

Birds are one of the most likely dispersal vectors for plants in Antarctica. We studied the nesting behavior of south polar skua (Catharacta maccormicki) and brown skua (Catharacta antarctica lonnbergi) to assess their potential role in ornithochory in the Argentine Islands - Kyiv Peninsula region. Nest samples were collected during 2009-2020 years in the Argentine Islands - Kyiv Peninsula region including all islands and coasts of the Graham Land from the Lemaire Channel to the islands of Berthelot Islands from north to south and extending from west to east from the Roca Islands, Cruls Islands, Rasmussen Point to the coast. We found that skuas utilize different nest building materials, including bryophytes, vascular plants (hairgrass Deschampsia antarctica), and lichens. In south polar skua nests, mosses and lichens dominate in the nest material; in brown skuas Deschampsia antarctica and mosses dominate. Both bird species likely collect nest components from nearby vegetation formations (<1 m distant). We conclude that C. maccormicki and C. antarctica lonnbergi are not selective in their choice of plant species, simply using the materials that dominate near the nest. Therefore, both species carry these materials from nearby sites, and only occasionally bring them from distant places.  In conclusion, for both species we did not find any evidence to support their involvement in long-distance ornithochory (stomatochory) in the region.