waders and their estuarine food supplies - Vlaams Instituut voor de ...

Na oi both Nrieck
Fig. 7. Numenius arquata. Search rate (step S ' > if all prey within a
3 minute period were N—^, N^^. or a mixture of both. Differences
are significant (R- = 64.2*. p < 0.001, n = 66). All data are Irom
male Curlews in late summer 1981,
taken from a water film also include filter-feeding
worms present in the entrance of a burrow.
Searching
A Curlew selecting Np,ck walked 3 times as fast as a
bird taking N^,,^ (Fig. 7). Prey of the N^ type are either
on the surface or in the burrow entrance and thus
easy to see. The high search rate is thus probably a way
to increase the encounter rate with potential prey. A
Curlew selecting N (iK does nol probe continuously in
order to find worms within reach. On the contrary, it
scans the surface carefully, apparently to detect tracks
left by Nereis. This is probably the reason the bird has
to walk slowly. There is evidence, however, lhat a
Curlew searching for N ^ does not simply sample
each burrow detected: 80 to 100% of all N^