Nesting habitat features are associated with ectoparasite loads in southern house wren nestlings in Argentina

Abstract Habitat modification can be associated with variation in host–parasite interactions by altering environmental conditions surrounding avian breeding sites. We investigated whether nesting habitat features were associated with ectoparasite load in nestlings of the Southern House Wren ( Troglodytes musculus ) breeding in nest boxes in tala woodlands of central-eastern Argentina. Over three breeding seasons, we quantified the prevalence and load of two major ectoparasite groups, Philornis aguapey larvae and hematophagous mites ( Ornithonyssus bursa and O. sylviarum ), and we evaluated associations with environmental variables on three different scales: inside the nest box, vegetation within 10 m of the nest box, and on a broader scale, the forest sector used for nesting by the Southern House Wren. Total Philornis larval load was higher in the exotic-tree sector than in the fragmented sector, whereas total mite load was lower in both the native and exotic-tree sectors than in the fragmented one. Within the native sector, mite load was negatively associated with the total number of trees and number of exotic trees within 10 m of nest boxes, although support for these associations was limited. The two ectoparasite groups thus showed contrasting spatial patterns among sectors, although the environmental factors underlying these differences remain unclear. The sectors differed in vegetation structure and composition; however, independent replication of sectors is needed to separate the influence of habitat characteristics from other site-specific factors. Our findings highlight the importance of considering multiple spatial scales and parasite groups when examining associations between habitat change and ectoparasite dynamics in avian hosts.