02016nas a2200181   4500008004100000245008400041210006900125300001200194490000800206520147900214653001301693653001101706653002201717100001801739700001301757700002501770856003901795       2008                        eng d00aPossible functions of alternative nests in raptors: the case of Bonelli's Eagle0 aPossible functions of alternative nests in raptors the case of B  a253-2590 v1493 aFour non-exclusive hypotheses have been proposed to explain the alternative nest-building behaviour of raptors: (1) nests as an advertising signal in territories, (2) frustration nests, (3) competition avoidance by nest-site and (4) reduction of nest ectoparasites. We report here data collected during an observational study of a population of Bonelli's Eagle Hieraaetus fasciatus in southeastern Spain. Our data does not support the first two hypotheses based on the closeness of nests within territories, the lack of correlation between the number of nests and the distance to neighbours and the construction of secondary nests at similar frequencies after breeding failures as after successes. In contrast, the construction of alternative nests to avoid competition with other cliff-nesting raptor species breeding nearby was clearly important since 30% of the pairs obtained some direct benefit from the existence of alternative nests within their territories. We also found abundant Coleoptera (Dermestidae) and Diptera (Carnidae, Calliphoridae and Phoridae) as ectoparasites in nests, and the alternative use of nests, synergetically with the presence of greenery as mechanisms for avoiding ectoparasites, was an important factor for the breeding success of the eagle. Our data suggest that competition avoidance and, in particular, the reduction of nest ectoparasite hypotheses are the more plausible explanations for the maintenance of alternative nests in raptors.10aCarnidae10aCarnus10aCarnus hemapterus1 aOntiveros, D.1 aCaro, J.1 aPleguezuelos, J., M.  u<Go to ISI>://WOS:000254237400014 