Bacteria in the reproductive tracts of Red-winged Blackbirds

We identified bacteria collected from the ejaculates and cloacae of male Red-winged Blackbirds (Agelaius phoeniceus) and from the cloacae of their mates during two breeding seasons and at three geographic locations with two distinct breeding habitats in each. In all, 42% of 233 ejaculates contained at least one bacteria species. Analysis of control samples suggested that some bacteria come from contamination during collection, but most are either carried within the ejaculate or are present on the male cloaca. As in an earlier study of Agelaius phoeniceus, we recorded many different species with considerable diversity between samples. We tested several explanations for this diversity. We found no overlap in either the presence of bacteria or the species found in multiple ejaculates obtained from the same male. We also found no association between bacteria in the ejaculate and those in the cloaca from the same male, or in samples collected from a male and those from the females nesting on his territory. Surveys of ejaculates from three locations, Kentucky, New York, and Wisconsin, yielded similar patterns of prevalence and diversity. Ejaculate samples from males inhabiting relatively dry upland habitats contained a similar number of bacteria and array of species as males inhabiting relatively wet, marshy territories. Many of the isolated bacteria are probably benign, but pathological effects of some species have been recorded in some circumstances. Our results suggest that acquiring pathogenic bacteria represents a potential cost to multiple mating by females, but the potential benefits of some microbes may offset these risks.