Graduate Exit Seminar
Linnea M. Rowse will present her Graduate Exit Seminar, Thursday, June 27 at 8:00 a.m. in 245 Kottman Hall. Her presentation is Pathways and Consequences of Contaminant Flux to Acadian Flycatchers (Empidonax virescens) in Urbanizing Landscapes of Ohio, USA.
Among environmental contaminants hazardous to humans and wildlife, mercury is of special concern due to its prevalence, mobility in aquatic systems, and persistence in sediments. Aquatic systems can have greater amounts of mercury in its bioavailable form (methylmercury) than terrestrial systems, and mercury can biomagnify through insects and be transported to terrestrial food webs (i.e., to aerial insectivores). Contaminant flux from aquatic to terrestrial systems is expected to disproportionately affect species reliant upon emergent aquatic insects, such as with aerial insectivorous birds. To understand the pathways of contaminant flux and the role that contaminants play in reproductive success, I addressed two broad questions: (1) Is avian exposure to metal contaminants influenced by territory placement at local and landscape scales? and (2) Do metal contaminants negatively impact individual body condition and reproductive output? I examined exposure of Acadian flycatcher (Empidonax virescens) to mercury in 19 mature riparian forest sites in central Ohio, USA during 2011-2012. At each site, I tested mercury levels in samples from river water, sediments, and emergent aquatic insects. I also determined Hg concentration in the blood of 76 breeding flycatchers and the season-long reproductive success (as measured by total number of fledglings per territorial male) of tested and banded individuals. Landscape factors including proximity of flycatcher territories to rivers (i.e., access to emergent aquatic insects) and amount of urbanization surrounding forest sites were not related to mercury levels in flycatchers, nor to mercury in sediment, water, or insects. However, when separately analyzed, a positive relationship between mercury in flycatchers and sediments emerged in urban landscapes alone. Although blood mercury levels were relatively low and appeared not to affect body condition, reproductive success declined with increasing mercury loads. My research suggests that pathways for contaminant flux from aquatic to terrestrial systems are complex and do not always follow predictable routes (e.g., positive relationship among Hg in sediment, aquatic insects, and flycatchers). Moreover, that reduced reproductive success was associated with trace levels of mercury in a free-living songbird is a cautionary note that wildlife managers should not overlook trace levels of contamination.