Woodpigeons nesting in association with hobby falcons: advantages and choice rules

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.