Fidelity of Overwintering Shorebirds to Roosts on the Moray Basin, Scotland: Implications for Predicting Impacts of Habitat Loss

Recommendations exist for reclaiming parts of the Special Protection Areas (SPAs) within the Moray Basin, Scotland that hold nine and six species of overwintering shorebird in nationally and internationally important numbers, respectively. Over 80% of estuaries in Britain are already affected by landclaim. To manage the effect of landclaim on shorebirds it is necessary to understand how they use the site for both foraging and roosting. Mark-recapture information gathered from overwintering Moray Basin shorebirds has allowed roost fidelity and movements among roosts to be determined and compared to other sites. Between 1977/78 and 1998/99, 43 593 adults and 19 318 juveniles of nine species of shorebird had been ringed or recaptured at 49 roosts on the Moray Basin. To analyse roost-fidelity the Basin was split into three sections according to geography, each section containing between 14 and 20 catching sites. Over 97% of within-year inter-roost movements of Eurasian Oystercatcher Haematopus ostralegus, Ringed Plover Charadrius hiaticula, Purple Sandpiper Calidris maritima, Dunlin C. alpina, Eurasian Curlew Numenius arquata, Common Redshank Tringa totanus and Ruddy Turnstone Arenaria interpres adults were within a section. Sixty-three percent of Red Knot Calidris canutus and 13% of Bar-tailed Godwit Limosa lapponica adult inter-roost movements involved changes of section. Roosting shorebirds moved short distances among roosts. Red Knot were the most mobile species (adults: 15.4 ± 1.5 km; juveniles: 17.7 ± 1.5 km) (P < 0.05), while Ruddy Turnstone, Ringed Plover and adult Eurasian Curlew were the least mobile species (mean: 0.7-1.3 km). Juvenile Dunlin moved further among roosts than adults (P < 0.01). Based on the frequency distribution of within-year among-roost movements, 50% and 75% of the respective populations of adult Eurasian Oystercatcher, Ringed Plover, Red Knot, Dunlin, Bar-tailed Godwit, Common Redshank and Ruddy Turnstone made use of roosts that were 3.8/1.0, 0.3/0.1, > 12/6.8, 6.2/2.5, 9.9/4.4, 4.8/1.3 and 5.7/3.1 km apart. Common Redshank and adult Dunlin on the Moray Basin and on the Wash, eastern England, moved similar distances (P > 0.05). Thus, these results may be of generic importance for these species. Red Knot and Eurasian Oystercatcher had different patterns of movement, possibly due to differences in prey availability on the two estuaries. A combination of food distribution, predation risk and disturbance may help explain the observed distances moved among roosts. From our results and the literature, we propose that the impact of a change in roost availability may be minimised by replacement roosts.