Many bird species nest in close association with other bolder and more aggr
essive birds which provide protection against nest predators. The woodpigeo
ns, Columba palumbus, that nest in poplar plantations in Northern Italy are
found almost exclusively clumped around hobby, Falco subbuteo, nests. Wood
pigeons settle in the area and build their nests after the hobby has starte
d nesting. We carried out experiments with dummy nests and observations on
woodpigeon nests. Dummy woodpigeon nests placed near a hobby's nest suffere
d less depredation by hooded crows, Corvus corone comix, than those placed
far from it. A logistic regression analysis showed that three variables, ho
bby nesting stage, distance from the hobby's nest and the hobby's aggressiv
eness, influenced the probability of nest predation. The degree of protecti
on varied during the hobby's nesting period and was highest when chicks wer
e in the nest. The hobby's aggressiveness against intruders varied both bet
ween and within individuals during different nesting phases. The predation
rate of dummy nests associated with the falcon was negatively correlated wi
th the ag,aggressiveness score of the hobby during the 6 days of dummy nest
exposure. Observations on real nests showed that woodpigeons selected hobb
ies that had a high fledging success, and a more vigorous defensive behavio
ur. Clues that would allow woodpigeons to choose the best protector may be
early nesting by the hobby and its aggressiveness. Hobbies preyed on adult
woodpigeons, but the risk incurred by the woodpigeons was low compared with
the very high risk of nest predation in this area. (C) 1999 The Associatio
n for the Study of Animal Behaviour.