Which are the visual cues used by a shiny cowbird host to discriminate parasite eggs?

DE LA COLINA, M. A.; REBOREDA, J. C.; MAHLER, B.

Pirenopolis, Brazil

Congreso; Animal Behavior Society 46th Annual Meeting; 2009

Animal Behavior Society

Of the highly polymorphic eggs laid by the shiny cowbird Molothrus bonariensis, one of its common hosts, the chalk-browed mockingbird Mimus saturninus, only rejects the immaculate eggs, which lack speckling. The aim of this study was to determine if this particular egg morph is detected as foreign due to following cues: UV reflectance and/or the absence of speckling. We artificially parasitized host nests with two sets of experimental eggs: 1) UV+ vs. UV-, and 2) speckled vs. uniformly colored. Brightness was similar for each pair of eggs. Rejection from the nest was recorded after 48 hs. We did not find increased rejection of UV+ or uniformly colored eggs, which suggests that these cues are not used by this host for parasite egg recognition. Moreover, we found different recognition abilities among the couples of M. saturninus, with the rejection of none, one or both experimental eggs depending on the couple. This indicates that there are interindividual differences in the detection of parasite eggs. These differences might be related to the experience of the couple or to different visual perception levels, but are in any case critical for studies involving parasitism rates.