PROTECTIVE ASSOCIATION AND BREEDING ADVANTAGES OF CHOUGHS NESTING IN LESSER KESTREL COLONIES

Some bird species may breed close to aggressive predators to reduce pr edation risk by more dangerous, generalist predators. We tested this p rotective nesting association hypothesis by studying solitary choughs, Pyrrhocorax pyrrhocorax, breeding within or outside lesser kestrel, F alco naumanni, colonies in northern Spain (1993-1994). We found 27 pot ential predators of choughs and kestrels and confirmed predation on ad ults and nests of both species by at least eight common predators. We experimentally assessed the defence investment of choughs and kestrels towards a stuffed eagle owl, Bubo bubo, in 19 buildings shared by bot h species. Lesser kestrels were more efficient at detecting the predat or, and defended more vigorously than choughs. Choughs clearly selecte d for breeding buildings where lesser kestrel colonies were installed. Breeding success of these choughs was much higher than that of chough s breeding alone, because of a lower percentage of nest failure. Benef its to choughs probably accrued from both the 'parasitism' of the kest rels' nest defence and the dilution of predation risk in the colonies. Since lesser kestrels do not prey on choughs, this could be a good ex ample of protective nesting association in birds. (C) 1997 The Associa tion for the Study of Animal Behaviour.