Use of agricultural fields by Ruffs staging in southwest Friesland in 20032013

Intensive dairy farming has changed the agricultural grassland areas of The Netherlands profoundly, with negative impacts on the reproduction of the shorebirds breeding there. This modern agricultural landscape also forms a staging site for migrating shorebirds, where they moult and replenish fuel stores, but staging performance in these areas has received much less attention. We studied northbound migrating Ruffs Philomachus pugnax staging in the grasslands of southwest Friesland over a ten year period, during which peak numbers declined from 20,000 in 2003 to 3500 birds in 2009 and then stabilized. On the basis of resighting locations of individually marked birds, we describe changes in their day-time foraging distribution from spring 2006 to spring 2013. Ruffs progressively retreated to the centre of the c. 10,000 ha study area, where, among intensive grasslands, established and newly created inland wetlands occurred that served as feeding and/or roosting sites. To quantify the spatial changes, in 2013 we repeated a transect survey of meadow use carried out earlier in 2003. Using similar characteristics of individual meadows in terms of herb richness (a measure of agricultural intensity) and landscape characteristics (distance to the roost, soil type), we show that, during spring 2013, as in 2003, Ruffs foraged preferentially on meadows close to roosting areas. The survey also highlights the preference of Ruffs for the Workumerwaard, a particularly large and open polder with a sandy soil and short vegetation bordered by a traditional roosting area on the shoreline. This study provides some evidence that inland wetlands may increase the attractiveness for migrating Ruffs of landscapes dominated by modern grasslands.