THE INFLUENCE OF A RIVER BIRD, THE DIPPER (CINCLUS-CINCLUS), ON THE BEHAVIOR AND DRIFT OF ITS INVERTEBRATE PREY

1. We examined the behavioural response of stream macroinvertebrates t o real and simulated predatory activity by a river bird, the Eurasian dipper, Cinclus cinclus L. 2. In the field, we assessed whether invert ebrate drift changed in response to live dippers in enclosures; we fou nd no effects on the drift of any of the five families for which indiv idual analyses were possible, either because it was infrequent, or inv olved distances too short to be detected (< 0.5 m). 3. In a laboratory stream, we observed prey during encounters with a model dipper which simulated flight, swimming, bill contact with the prey, and stone turn ing. invertebrate families varied in their response. Simuliids and hyd ropsychid caddis lacked effective escape behaviour, consistent with he avy losses through predation by dippers in the wild. Other families ei ther drifted (Baetidae, Gammaridae) or moved away (Heptageniidae, Ephe merellidae, Leuctridae, Perlidae) from the model dipper, but responded only to bill contact or simulated stone turning. Such delayed respons es would not protect individuals directly targeted by foraging dippers and partly explain the lack of detectable effects by dippers on drift in the field. 4. We suggest why invertebrates do not show more marked escape responses to this important predator.