Disease ecology of a population of Eastern Bluebirds (Sialia sialis) in Georgia

Abstract

A population of Eastern Bluebirds (Sialia sialis) nesting within three grass-dominated agricultural sites in northwestern Georgia was monitored to estimate survival and reproduction, establish baseline physical and hematological parameters, and survey infectious agents as a preliminary investigation of the effects of infectious agents on bluebird population dynamics. Adult and nestlings were captured, marked with aluminum leg bands, and released during the breeding seasons (April through August) of 2004 through 2006 in order to estimate survival. Adult survival was not associated with nesting site, whereas nestling survival varied by site. Adult males and females differed in body condition and packed cell volume only. Adult packed cell volume and total plasma protein was higher than that of nestlings. Ten species of macroparasites, 5 species of protozoa, 43 species of bacteria, and 1 virus were detected by live examination, examination of blood smears and feces, necropsy, DNA extraction, and examination of nesting materials. Exploratory analyses suggested differences in parasite prevalences may have been associated with site characteristics. Reproduction varied among years but not among sites. Hematophagous nest mite populations were manipulated within nest boxes using a pyrethrin treatment to evaluate the effect of blood loss on nestlings. Nestlings in both treatment and control groups survived to fledging and did not differ in body mass or tarsus length, but nestlings from treated boxes had higher levels of hemoglobin and lower numbers of immature erythrocytes than nestlings from untreated boxes.