Endocrine disrupting chemicals (EDCs) produce changes in physiology and behavior via diverse mechanisms including acting as hormone mimics or antagonists, affecting intracellular signaling pathways, and altering hormone production pathways. The fungicide vinclozolin acts as an anti-androgen and is known to affect affiliative behaviors in rodents, fish and amphibians. To investigate the possible effects of exposure to EDCs on reproductive behavior in a wild population of songbirds, we examined the effects of vinclozolin in wild-caught Dark-eyed Juncos (Junco hyemalis). For this and many other temperate songbird species, testosterone has powerful activational effects on affiliative behaviors in adulthood. We hypothesized that vinclozolin would affect male behaviors associated with female preference. Male juncos received daily oral gavage for 10 weeks with 2mM vinclozolin in vehicle or vehicle alone. Juncos were photostimulated (16L:8D) to induce breeding behavior. Each pair of a treated and non-treated male was presented to an estrogen-primed female to assess female preference. Seven of eight females exhibited a strong preference for a male exposed to vinclozolin over a control male (p=0.01). The only significant difference in measured male behaviors was increased beak wiping in controls (p=0.006) and there was no difference in gonad size or brain weight (p>0.05 for each). Our data suggest that estrogen-primed female juncos prefer to associate with male juncos exposed to this anti-androgen. This finding demonstrates that environmentally occurring anti-androgens can affect the social behavior of this species. To our knowledge, this is the first study to show that vinclozolin has effects on the social behavior of songbirds.