Voedsel van de Regenwulp Numenius phaeopus in het voorjaar in Noord-Drenthe

Food choice of Whimbrels was studied in northern Drenthe in spring. Pellets were collected at a roost on 11 May 1995 (n=82, of which 38 and 32 were analysed microscopically to check for earthworms and leatherjackets respectively). Mean pellet size was 22.6x15.0 mm, mean dry weight 0.6 g (Table 1). Most pellets contained grass particles and sand, presumably swallowed together with prey items. Earthworms and insects were most frequently encountered in the pellets (Table 2), followed by leatherjackets. This accords rather well with observations of foraging Whimbrels; of 64 identified prey items, 44 were earthworms and 20 leatherjackets. The presence of Whimbrels in northern Drenthe coincides with peak biomass of earthworms and leatherjackets in grassland. However, harvestability of these prey species shows wide annual fluctuations, depending on the moisture of the top layer of grassland. During the last decade, improved drainage has probably reduced the period of availability of main prey species, which may partly explain the decline in numbers of Whimbrels staying in northern Drenthe in spring.