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.IntroductionFlocks of Common Scoters Melanitta nigra passing coastal watchpoints in spring and autumn on their way to and from breeding grounds in Scandinavia and Russia are a familiar sight for many birders in Britain and Ireland. Around 130,000 Common Scoters are estimated to winter in Britain (Frost et al. 2019), which equates to around 12% of the estimated global population (BirdLife International 2021). Common Scoters are concentrated at a relatively small number of sites in Britain, including Liverpool Bay (Lancashire & North Merseyside), Carmarthen Bay (Carmarthenshire), the Moray Firth (Nairn/North-east Scotland) and off the north Norfolk coast (Musgrove et al. 2011). These populations make use of migratory staging points, such as Aberdeen Bay (North-east Scotland) and the Solway Firth (Cumbria/Dumfries & Galloway), with the latter holding up to 8,000 birds in May and June and up to 6,000 in August and September (Hartley 2007; Lewis et al. 2008).Overland migration of Common Scoters in England has been documented for over 140 years; Eagle Clarke described three nights of Common Scoter migration over Skipton, Yorkshire, on 24th–26th April 1879 (Clarke 1880). In 1950, east-to-west autumn migration of Common Scoters over the Midlands was mooted (Raines 1950) and, by 1969, three peak periods of Common Scoter migration had been established across northern England: in April, in July–August, and in October–November (Spencer 1969). The same trend was observed in the West Midlands (Hawker 1970), with the contemporaneous description explicitly highlighting that movements across the region did not coincide with periods of poor weather as had previously been suggested (e.g. Baxter & Rintoul 1953, Bannerman 1958, Atkinson-Willes 1963, Ruttledge 1966). Spencer and Hawker also note that the first two passage periods consisted of predominantly males based on visual observation of birds, which were outnumbered during the autumn by female and immature birds.