Habitat preferences of waders (Charadrii) on the coast of the Orkney Islands

Abstract

Capsule Twelve species of wader were surveyed on 494 coastal sections, revealing features in addition to substratum type that are important in habitat selection. Aims To determine which habitat characteristics affect the probability of waders occurring on coastal sections of Orkney in winter, and to measure the strength of these habitat preferences. Methods A total of 494 sections of shoreline in the Orkney Islands were surveyed for 12 species of wader in winters 1982/3 and 1983/4. A series of environmental variables (exposure, substratum type within the inter-tidal zone, shore width and steepness) were noted in the field and taken from maps. Logistic regression models were used to examine the probability of a given species occurring on a section, with given physical characteristics. Results Ringed Plover Charadrius hiaticula, Sanderling Calidris alba and Bar-tailed Godwit Limosa lap-ponica preferred sand shores; Lapwing Vanellus vanellus, Snipe Gallinago gallinago, Redshank Tringa totanus, Curlew Numenius arquata and Dunlin Calidris alpina preferred mud; Oystercatcher Haematopus ostralegus, Golden Plover Pluvialis apricaria and Purple Sandpiper Calidris maritima preferred rock; and Turnstone Arenaria interpres preferred gravel and rock shores. The strength of a preference for substratum type was greatest in Sanderling, Bar-tailed Godwit, Lapwing and Purple Sandpiper, and least in Oystercatcher, Curlew, Golden Plover and Turnstone. Some species displayed additional preferences for exposed shores (Purple Sandpiper, Ringed Plover and Bar-tailed Godwit), sheltered shores (Curlew and Redshank) and wide shores (Sanderling, Purple Sandpiper, Dunlin, Bar-tailed Godwit and Turnstone). No species preferred steep shores or cliffs. Conclusions Simple habitat descriptions coupled with map-derived variables, can provide an initial insight into the habitat preferences of waders. Further work relating wader distribution to invertebrate food supplies is required.