Black-headed Gull (Larus ridibundus L.) as a Keystone Species in the Lake Bird Community in Primary Forest-Mire-Lake Ecosystem

• Main Authors: Leito, Aivar, Leivits, Meelis, Leivits, Agu, Raet, Janar, Ward, Raymond, Ott, Ingmar, Tullus, Hardi, Rosenvald, Raul, Kimmel, Kai, Sepp, Kalev
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Common tern; Sterna hirundo; Black-headed Gull; Larus ridibundus
• Online Access: http://eprints.brighton.ac.uk/15564/; http://eprints.brighton.ac.uk/15564/1/Leito%20et%20al%20_Baltic%20Forestry%202016%201_34-45%20psl.pdf

Within animal communities the loss of a single keystone species can lead to substantial change, or in extreme cases, community collapse. This phenomenon has been documented in different communities and habitats but has not been widely investigated in bird communities. We studied the long-term dynamics of breeding birds in a medium-sized hemiboreal lake that is situated within a large primary forest-mire-lake ecosystem in central-east of Estonia. The aim of this 25 year study was to determine whether the black-headed gull, Larus ridibundus, acts as a keystone species in the bird community and what was the effect of the loss of this species. Results revealed large changes in the bird community similar to those that would occur in a fragile system in response to keystone species loss, confirming our theory. Mallard Anas platyrhynchos, common pochard Aythya ferina, tufted duck Aythya fuligula, great crested grebe Podiceps cristatus, red-necked grebe Podiceps grisegena, Eurasian marsh harrier Circus aeruginosus, spotted crake Porzana porzana, coot Fulica atra, and common tern Sterna hirundo were most closely related to the abundance of black-headed gull. During the study period there was little change in habitat quality or extent. It is unclear as to the causes of the gull colony collapse; however, landscape-level changes in feeding areas and agricultural land could be a reason. We conclude that further study of keystone species and fragile communities in different habitats and ecosystems is important to ascertain which species and communities are most likely to be affected in the event of the loss of a keystone bird species.