Migrations, Destinations and Breeding of Eurasian Curlews Numenius arquata arquata that Spend the Non-Breeding Season in Northern Scotland

Abstract

The conservation of Eurasian Curlews, whose numbers are declining, is aided through an understanding of environmental challenges faced by the birds throughout the annual cycle. In the Moray Firth, northern Scotland, 48 non-breeding Curlews were tagged with geolocators to describe their migrations (routes, destinations and timing), time of breeding and nest success. Based on 19 recaptures, breeding destinations included northern Scotland (21% of tagged birds), Norway (32%), Sweden (21%) and Finland plus Russia (26%). These percentages matched closely with the results from earlier ringing recoveries/sightings. The median last date in the non-breeding area varied for the Fennoscandian birds: 31 March for those migrating to Norway, 11 April for Swedish birds and 15 April for Finnish birds. The amount of migratory fuel accumulated prior to departure in early April was 10–13% of the late winter mass, sufficient for a 1000-km flight, which was similar to the median distance to Norwegian, but not Swedish or Finnish, destinations. Staging en route characterised the migrations to these latter destinations, resulting in longer migration times. Most of the Fennoscandian Curlews migrated across the North Sea with a tailwind component in spring, but all had a headwind component in autumn. A first-year bird remained in northern Scotland for the first summer, but migrated to Russia in the second and did not nest. Arrival on the breeding grounds varied significantly according to destination. Males and females incubated at different parts of the 24-hour cycle, even although there were 24 hours of daylight for most birds. Of birds that nested, 63% hatched clutches, some after a second attempt. Periods of 24 hours of daylight masked the initial departure from the breeding grounds, so only the latter part of the autumn migration and first date back at the non-breeding area were recorded (11 July), with no difference among the Fennoscandian breeding birds.