Reboreda, J. C., University of Buenos Aires, Buenos Aires, Argentina,
Chomnalez, M. ., University of Buenos Aires, Buenos Aires, Argentina,
Di Giacomo, A. G., Asociación Ornitológica del Plata, Buenos Aires, Argentina,
Mahler, B. ., University of Buenos Aires, Buenos Aires, ,


We analyzed host use by Shiny Cowbirds (Molothrus bonariensis) at four sites of Argentina corresponding to three biogeographic regions: Pampa grasslands, Espinal shrublands and Chaco woodlands. For each site we determined: frequency of parasitism in available hosts; association between frequency of parasitism and host's body size, nest type, and genetic distance between host and parasite; and if frequency of parasitism in same hosts was similar at different sites. In all sites few hosts were parasitized at high frequencies (>50%), and the majority of potential hosts were not parasitized or parasitized at low frequencies (<25%). Frequency of parasitism was negatively associated with host body size in two sites, higher in open than in closed nests in two sites, and negatively associated with genetic distance between host and parasite in two sites. Frequency of parasitism of same hosts in different sites was positively associated, but several hosts were highly parasitized in one site and not parasitized in the others. Our results indicate that at local-regional level Shiny Cowbirds are less generalists than previously assumed and that host preferences vary considerably between regions.

Oral presentation

Session #:G03
Date: Tuesday, 8/5/08
Time: 2:45 PM

Presentation is given by student: No