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

Many bird species nest in close association with other bolder and more aggressive birds which provideprotection against nest predators. The woodpigeons, Columba palumbus, that nest in poplar plantations inNorthern Italy are found almost exclusively clumped around hobby, Falco subbuteo, nests. Woodpigeonssettle in the area and build their nests after the hobby has started nesting. We carried out experimentswith dummy nests and observations on woodpigeon nests. Dummy woodpigeon nests placed near ahobby’s nest suffered less depredation by hooded crows, Corvus corone cornix, than those placed far fromit. A logistic regression analysis showed that three variables, hobby nesting stage, distance from thehobby’s nest and the hobby’s aggressiveness, influenced the probability of nest predation. The degree ofprotection varied during the hobby’s nesting period and was highest when chicks were in the nest. Thehobby’s aggressiveness against intruders varied both between and within individuals during differentnesting phases. The predation rate of dummy nests associated with the falcon was negatively correlatedwith the aggressiveness score of the hobby during the 6 days of dummy nest exposure. Observations onreal nests showed that woodpigeons selected hobbies that had a high fledging success, and a morevigorous defensive behaviour. Clues that would allow woodpigeons to choose the best protector may beearly nesting by the hobby and its aggressiveness. Hobbies preyed on adult woodpigeons, but the riskincurred by the woodpigeons was low compared with the very high risk of nest predation in this area.

Giuseppe Bogliani, Fabrizio Sergio & Giacomo Tavecchia, ANIMAL BEHAVIOUR, 1999, 57, 125-131