Nocturnal overland migration of Common Scoters across England

Metcalf, Oliver C, Bradnum, David, Dunning, Jamie and Lees, Alexander ORCID: https://orcid.org/0000-0001-7603-9081 (2022) Nocturnal overland migration of Common Scoters across England. British birds; an illustrated magazine devoted to the birds on the British list, 115 (March). pp. 130-141. ISSN 0007-0335

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Abstract

A significant proportion of the world’s Common Scoters Melanitta nigra spend the non-breeding season in the coastal waters around Britain and Ireland. Overland movements of scoters across Britain were first documented over 140 years ago but the prevailing assumption in the ornithological literature has been that their primary migration routes are largely coastal. With the increased uptake of nocturnal migration monitoring, it has become apparent that Common Scoters are a seasonally predictable feature of the night-time soundscape across Britain, even at inland locations. We crowdsourced records of nocturnally migrating Common Scoters from England in the spring of 2020 to try and assess the migration routes taken. We combined this data with 20 years of reported sightings of inland Common Scoters to assess the phenology of these events. Our results suggest that Common Scoters from a number of geographically disjunct wintering areas move overland across England in spring using several potentially discrete migration routes, and that the timing of overland migration differs between the north and south of England. Across the whole of England, adult male Common Scoters formed the majority of reports in spring (62%) and summer (67%). However, in the late autumn period, the proportions were reversed, with 67% of birds concerning females or immatures. These trends were consistent across the three regions studied – the north, the midlands and the south – with the largest disparity between the sexes occurring during summer in the north of England, where 70% of the reports concerned drakes.