Provisioning response to manipulation of apparent predation danger by parental Pied Flycatchers

We tested whether nest visitation rate of parent pied Flycatch ers (Ficedula hypoleuca) is decreased by an experimentally increased predation risk. We simulated predation risk by placing a stuffed Pygmy Owl (Glaucidium passerinzm) in the nest vicinity and by playback of pygmy owl's whistling. We used Blackbird (Turdus merula) treatment as a control. Surprisingly, the parental nest visitation r ate was about 25Va higher in the treatment thar in the control group. The treahnents were reversed on the same day. Pairs of the "confol treatment" in the first phase increased their nest visitation rate by 167, as a response to the "owl treatment". Four possible explanations exist. parents may increase delivery in order (1) to silence the begging of the nestlings, who might otherwise betray the nest location to the owl, or (2) to increase the growth rate of the nestlings so that they fledge sooner, probably disperse better and so elude the danser. Altematively, (3) the parents may view a predator as a threat to themselves. Ld remain in the vicinity of the nest where they are most familiar and therefore safest. In addition, (4) increased nest visitation might form part of nest defense behaviour against the owl.