Offspring age and nest defence: test of the feedback hypothesis in the meadow pipit

The feedback hypothesis has been proposed to explain variation in nest defe nce intensity in birds. In species in which the female builds the nest and incubates the eggs, this hypothesis predicts a higher level of nest defence initially for females, whereas males' responses should increase when they start feeding nestlings. We studied changes in nest defence by both sexes d uring the nestling period in meadow pipits, Anthus pratensis. We placed a s tuffed stoat, Mustela erminea, 5 m from a meadow pipit nest with nestlings aged either 2-4 or 7-12 days and recorded the nest defence behaviour of bot h parents for 10 min. Males came closer to the predator and mobbed more int ensely for older nestlings whereas females defended the nest at a high inte nsity from the beginning of the nestling period. This finding agrees with t he predictions of the feedback hypothesis. We also discuss possible functio ns of alarm calls and number of mobbing birds during nest defence. (C) 2001 The Association for the Study of Animal Behaviour.