Arrival and Departure Patterns of Eurasian Curlew Numenius A

155 Arrival and departure patterns of Eurasian Curlew Numenius a. arquata wintering on the River Severn estuary, Gloucestershire, southwest England JOHN D. SANDERS1,* & EILEEN C. REES2 118b Cleevelands Drive, Cheltenham, Gloucestershire GL50 4QF, UK. 2Wildfowl & Wetlands Trust, Martin Mere, Fish Lane, Burscough, Lancashire L40 0TA, UK. Correspondence author. E-mail: [email protected] Abstract Regular spring and autumn observations of colour-ringed Eurasian Curlew Numenius a. arquata wintering on the River Severn estuary in Gloucestershire, UK, marked during 2010–2013 inclusive, were used to locate surviving ringed individuals (n = 147 birds resighted) and describe the timing of their annual arrivals and departures. Breeding locations reported for 18 birds were from Fennoscandia (5), the Netherlands or Germany (6) and Britain (7). Fennoscandian birds remained significantly later on the estuary each year than the 13 individuals known to breed in Britain, the Netherlands or Germany. Departure dates recorded for 109 Curlew during a more intensive survey in 2016 similarly found that onset of spring migration was significantly later for birds known (or thought because they remained on the estuary until April) to be of Fennoscandian origin. Curlew returned from breeding grounds to the Severn estuary from the first week of June onwards, sooner than reported in previous studies, but with limited evidence for differences in return dates for Curlew breeding in different parts of Europe. Whether early arrival is associated with a failed breeding attempt could not be determined. Key words: breeding distribution, colour-marked individuals, movements, winter arrival dates, winter departure dates. Eurasian Curlew Numenius a. arquata have 2017–2018 (Gloucestershire Naturalists’ been counted on the lower reaches of the Society, P. Hazelwood and J. Sanders, River Severn estuary in Gloucestershire, unpubl. data). This concurs with counts UK, since 1963, where up to 1,400–1,800 made during the UK’s mid-monthly Wetland birds were recorded during the late 1970s to Bird Surveys (WeBS), which reported early 1980s. More recently, numbers on this declining numbers wintering across a larger part of the estuary have declined to annual part of the estuary from c. 4,500 birds maxima of c. 1,000 in 2013 and c. 800 in in winter 1992/93 to c. 3,000 by winter ©Wildfowl & Wetlands Trust Wildfowl (2018) 68: 155–171 156 Migration phenology of Curlew wintering in southwest England 2008/09 (Waters & Cranswick 1993; Calbrade February (Bainbridge 2002). Radar studies et al. 2010). Curlew migrate to British by Lack (1962) of waders returning to wintering sites from breeding areas across their wintering grounds reported that early Europe, including from other parts of migration of Curlew from mainland Europe Britain, the Netherlands, Germany and into East Anglia occurred in late June to Fennoscandia (Bainbridge & Minton 1978; early July, and more recently Bainbridge Brown 2015). The distribution of the British- and Minton (1978) found that although breeding population contracted (Balmer et al. most movements of Curlew breeding in 2013), and numbers declined by 48% Britain and Ireland begin in August, early between 1995 and 2014 (Baillie et al. 2010; movements of failed northern breeders and Harris et al. 2016), most likely because of females occur in July. Although both sexes factors such as intensification of agriculture, care for and brood the young post-hatching forestry and increased egg and chick (Cramp & Simmons 1983), British-breeding predation (Grant et al. 1999; Brown et al. 2015; males remain a little later to tend the chicks Franks et al. 2017). Numbers breeding in in late June and July, whilst the young Belarus, Belgium, Denmark, France and are learning to fly (Bainbridge 2002; M. Germany have been stable or increasing Smart in litt.). The review by Cramp and during the 1990s–2000s (Brown 2015), in Simmons (1983) additionally suggested that contrast to other common waders such as Fennoscandian Curlew begin to arrive in Northern Lapwing Vanellus vanellus, Redshank North Sea estuaries to moult in July–August. Tringa totanus and Common Snipe Gallinago Overall, the studies therefore indicated that gallinago (Heldbjerg & Eskildsen 2009; the majority of adult birds from the different Calbrade et al. 2010; BirdLife International breeding areas are probably at their wintering 2018). Given the variation in trends noted sites in Britain by the end of September. for the species across Europe, data on During the 1960s–1970s, small numbers the breeding distribution and migration of Curlew on the Severn estuary were phenology of individuals observed on the caught by members of the former Severn wintering grounds may provide insight into Vale Ringing Group and fitted with metal any differences in trends in numbers recorded rings, yet little is known about the timing of for Curlew at wintering sites within the UK. movements and breeding distribution for Although relatively little is known about birds wintering at the site. More recently, the timing of Curlew movements to and eight years of observations (August 2011– from their wintering sites in Britain, adult April 2018) of 165 Curlew colour-ringed Curlew which remain at British coastal at a high tide roost near Wibdon (51.664°N, sites as late as April are considered to be 2.620°W) during 2010–2013 inclusive of Fennoscandian origin (Evans 1966; indicated high levels of winter site fidelity Bainbridge 2002), whereas British-breeding (Sanders 2017). From over 10,000 resightings Curlew disperse to their breeding areas of 147 colour-ringed birds at or near the earlier, such that many breeding areas in ringing site in at least one winter after southern Britain are reoccupied during ringing (Sanders 2017; J. Sanders, unpubl. ©Wildfowl & Wetlands Trust Wildfowl (2018) 68: 155–171 Migration phenology of Curlew wintering in southwest England 157 data), only one is known to have moved to September 2010, attempts were made each another estuary, in Cornwall (M. Grantham, spring and autumn to find and identify every pers. comm.). That the same marked birds marked bird in the Gloucestershire section return to the estuary each year provides of the estuary between the harbour at an excellent opportunity for analysing Lydney (51.710°N, 2.508°W) and the first the timing of their movements, and (for road crossing of the River Severn (51.609°N, individuals identified on the breeding 2.638°W). Individual identification was not grounds) to determine whether arrival and straightforward; birds were marked with departure patterns vary with breeding different colour rings on both the left and distribution. Adult Curlew remaining in right tibiae, so observations of both legs Britain into April are thought to be were essential to confirm identity. Mudflat- of Fennoscandian origin (Evans 1966; feeding birds were usually observed c. 0.5 Bainbridge 2002), so the presence of over km away, making ring identification difficult, 505 Curlew counted on the Gloucestershire and when closer on the high tide roosts the sections of the Severn estuary between 8–10 Curlew usually stood on one leg. Optimum April 2015 (out of about 900 present earlier ring reading time was during first arrival at in the winter; J. Sanders pers. obs.) suggests the roost when both legs were still visible. that just over half of the birds wintering in Close viewing was essential to ensure Gloucestershire migrate to Fennoscandia. correct colour ring identification, confirmed This paper analyses the sightings of by digiscope images, made from behind a colour-marked Curlew on the Severn screen set before the first birds arrived (at Estuary from 2011 onwards, to describe least 3 h before each high tide) to minimise arrival and departure patterns for disturbance. Observation periods at Wibdon comparison with the earlier studies of the and at five other high tide roosts in the study species’ migration phenology. As adult area were governed both by the timing of female Curlew depart from their breeding the tides and weather conditions, clustering grounds first, leaving males to tend the sightings at two-week intervals. Guscar young (Bainbridge & Minton 1978; Rocks (51.682°N, 2.586°W) and Littleton Bainbridge 2002), whether females returned Warth (51.621°N, 2.593°W) were best to their winter quarters earlier than males viewed on spring tides which push the birds was investigated. Sightings in the breeding further up the shore, while Aylburton Warth range are also reported, with an analysis of (51.692°N, 2.554°W), Wibdon, Pillhead the arrival and departure dates recorded for Gout (51.629°N, 2.584°W) and Shepperdine these individuals, to relate timing of spring (51.656°N, 2.568°W) were best observed on and autumn migration to their breeding neap tides. distribution. Determination of Curlew departure in late winter and early spring was confounded Methods by the dispersal of birds over wide areas on Following the colour-ringing of 165 Curlew both sides of the estuary and field-feeding, caught at Wibdon on the Severn Estuary in rather than being concentrated at high tide ©Wildfowl & Wetlands Trust Wildfowl (2018) 68: 155–171 158 Migration phenology of Curlew wintering in southwest England roosts. Recording became easier in late March Britain or elsewhere in Europe. These birds and April, when birds returned to feed on were grouped into three breeding locations, the estuary and daylight hours were longer, based on the assumption that they would making it possible to record the number and be philopatric in the breeding range: identity of colour-ringed individuals that Fennoscandia, England and the Netherlands/ stayed into April. A more intensive study Germany. As some Curlew were seen over was carried out during 2016, particularly several years, the average departure week during February–April (n = 41 visits; and average return week was calculated for average = 13.7 visits/month) and June– each bird to control for repeat observations August (n = 32 visits; average = 10.7 visits/ of the same individuals in the data.

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