Background/Question/Methods Polychlorinated biphenyls (PCBs) have emerged as a harmful, worldwide chemical pollutant. Most research emphasizes only the lethal effects of PCBs, concentrates on presence/absence data, and necessitates destructive sampling. The goal of this study was to address these deficits in our knowledge of PCBs, with the aim of developing a non-invasive, reliable indicator of the effects of PCBs. Bird populations may be especially sensitive to low concentrations of PCBs, which can cause neurological damage, and mimic estrogenic activity, thereby altering sexual development and reproduction. These studies suggest that sublethal PCB exposure may be deleteriously affecting wildlife populations. In songbirds, these features are expressed behaviorally in characteristics of song, suggesting that PCB exposure could be monitored through changes to song characteristics. Moreover, PCBs have been shown to directly affect the brain regions involved in song learning and production. Thus, I hypothesized that birdsong could be adversely altered by sublethal PCB effects, and could be used as a behavioral indicator of PCB presence. To test whether birdsong can be used to indicate sublethal PCBs bioavailability in the environment, I performed a two-year (2006-2007) survey of Black-capped Chickadee (Poecile atricapillus) fee-bee songs along a PCB gradient. Results/Conclusions All songs were analyzed for 1) differences in the interval ratio (a measure of song quality) among locations, and 2) the interval ratio variation between and within individuals. As predicted, characteristics of song quality were altered in the presence of PCBs. For example, analyses suggest that in 2006 the average interval ratio was lower in the low PCB site (P<0.001) than in the higher PCB site. Furthermore, variation in the interval ratio indicates song learning appears to be affected by PCBs, but not song production. My results support the hypothesis that non-lethal levels of PCBs in the environment have significant effects on the sensitive song system in common passerines. This research will provide a possible non-invasive bioindicator of PCB levels in riparian habitats and adds novel understanding of the effects of sublethal chemical pollution.