Laagwaterverspreiding van steltlopers in de Waddenzee

Metawad is a five-year research project funded by Waddenfonds that started in 2011. One of its aims is to investigate how population changes of migrating shorebirds are driven by changes in the conditions in their main feeding habitat, intertidal mudflats. We investigate how differences in survival may be preceded by differences in behavioural indicators related to foraging, which in turn may be driven by factors like food, forager density and distribution, and predation danger. Metawad focuses on five long-distance migrant species differing in feeding habits and migration routines: Brent Goose Branta bernida, Eurasian Spoonbill Platalea leucorodia, Bar-tailed Godwit Limosa lapponica, Red Knot Calidris canutus and Sander-ling Calidris alba. To put the data on these target species in a wider context, we started off by mapping the low tide distribution of a wider array of shorebird species in the Dutch Wadden Sea, with the aim to link this (at a later stage) to available food stocks, which are monitored throughout the Dutch Wadden Sea (Fig.1). Here we focus on the eight most numerous species: Curlew Numenius arquata, Oystercatcher Haematopus ostralegus, Bar-tailed Godwit, Grey Plover Pluvialis squatarola, Red Knot, Redshank Tringa totanus, Sanderling and Dunlin Calidris alpina. The eastern parts of the Wad-den Sea supported the lowest densities of all species except Grey Plover and Dunlin (Fig. 2). Overall, Dunlin was most abundant, followed by Red Knot and Oystercatcher (Fig. 3). Packing densities, however, were highest in Red Knot, followed closely by Dunlin, and then by Sanderling, Oystercatcher and Bar-tailed Godwit (Fig. 3). It is discussed why in Red Knots and Dunlin packing densities were much higher than in a similar study on low tide distribution mapping (but from another year), and than densities estimated from high tide counts (also from another year). For instance, the high packing densities in our study may be related to a substantial spat fall of Cockle Cerastoderma edule in 2011. In further steps we will examine the relationships between the distributions of birds and their food stocks. Assuming that birds optimize their behaviour, for the best studied bird species, individual characteristics like body weight, gizzard size, and activity pattern, can serve as predictors of their distribution. We aim to link these features to survival of marked birds in order to better understand the complex relationship between population dynamics of shorebirds and the state of the habitats they live in