Breeding Common Scoters Melanitta nigra in Scotland’s Flow Country: a population in decline despite productivity being stable

Abstract

ABSTRACT Capsule The breeding productivity of the Common Scoter population in Scotland’s Flow Country remained relatively stable during a 44% population decline in Britain and Ireland. Aim To investigate breeding productivity changes in the eastern Flow Country’s Common Scoter population over 22 years and identify possible threats and causes of change during a period of national population decline. Methods Common Scoters from 32 breeding sites were surveyed annually between 2002 and 2023. Each site was visited two to three times in May (pre-nesting period) and two to three times in July and August (post-hatching period) to record the numbers of adult and juvenile Common Scoters. Results Between 2002 and 2023, whilst the Common Scoter population declined (approximately 44% from 27 to 15 breeding pairs) across the study area, breeding productivity (defined as large ducklings per female) remained stable, averaging 0.44 (range of annual means 0.00–1.06) large ducklings per female. The number of small ducklings per female also remained relatively stable. A year of higher breeding productivity did not result in an increase in the number of breeding females in the following years, suggesting that the cause of the population decline lies away from the breeding region. Conclusion Breeding productivity needs to increase, and poor breeding seasons need to be prevented to help maintain this population. The causes of the Common Scoter’s decline away from the breeding area need to be resolved to prevent local extinction. This could be assisted with the removal of non-native forestry plantations in the area, which has been observed to benefit other ground-nesting species by alleviating predation pressure, and by maintaining lake habitat quality, as reflected in shallow water and abundant large invertebrates.