Volume 49, No. 2

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Threats and conservation status of Common and Roseate terns Sterna hirundo/S. dougallii in the Azores: A case study for Terceira Island


1Azorean Biodiversity Group, University of the Azores, Rua Capitão João d'Ávila, 9700-042 Angra do Heroísmo, Terceira, Azores, Portugal (
2Terceira Natural Park, Regional Directorate for the Environment, Rua do Galo 118, Azores, 9700-091 Angra do Heroísmo, Terceira, Azores, Portugal
3Marine & Environmental Sciences Centre, Institute of Marine Research & Okeanos, Department of Science and Technology, Azores University, 9901-862 Horta, Faial, Azores, Portugal


LAMELAS-LÓPEZ, L., PIETRZAK, M., FERREIRA, M. & NEVES, V.C. 2021. Threats and conservation status of Common and Roseate terns Sterna hirundo/S. dougallii in the Azores: A case study for Terceira Island. Marine Ornithology 49: 301 - 309

Received 02 March 2021, accepted 28 June 2021

Date Published: 2021/10/15
Date Online: 2021/10/14
Key words: seabirds, North Atlantic, Macaronesia, camera traps, depredation, introduced mammals, control actions


The Azores Archipelago holds the second most important population of Roseate Terns in the North Atlantic. However, the size of the population has been decreasing. In this study, we used remote-sensing cameras and visits to the main colonies of Common Terns Sterna hirundo and Roseate Terns S. dougallii on Terceira Island to identify the causes of breeding failure. Nest depredation by introduced mammals, particularly rats and cats, was the main cause of breeding failure, leading, in some cases, to the complete destruction of the colony. Additional threats included nest disturbance by humans and dogs, which caused the destruction of some nests. Measures aimed at mitigating depredation were tested but in the case of rodents, control plans proved difficult to achieve. This is probably because rodents are widespread in the Azores, they are not limited by food resources, and/or trapping methods are ineffective.


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