House Wren (Troglodytes aedon)
The house wren is the most commonly encountered songbird that was studied on the Tittabawassee River; however, given their small size, cryptic brown coloring, and reclusive behavior they are often only heard along the forest/field edges along the river. Our research aimed to verify that the house wren populations that reside within the Tittabawassee River floodplain were not experiencing adverse effects from site-specific contaminants, in particular, dioxins and furans.
The house wren possesses many ideal attributes of a study species for assessing bioaccumulative compounds in the environment, including being obligate cavity-nesters, having a widespread distribution both locally and nationally, being limited in foraging range during nesting, being resistant to disturbances while nesting, and being relatively abundant on site.
To define their dietary exposure to contaminants, site-specific diets of the house wren were determined through the collection of bolus samples. Bolus samples were collected from nestling birds between the ages of 3 and 9 days old by putting a restrictive device around their throat to prevent them from swallowing prey items brought to the nest by adults while still allowing them to breathe normally. The device was left in place for 30 to 45 minutes, after which the samples were collected and the device removed. The site-specific dietary composition was then determined by identifying the individual insects represented. These prey items were then collected from the study area by the research team and analyzed for contaminant concentrations. For the house wren, this prey items included mostly moths, caterpillars, grasshoppers, and spiders. These collections allowed us to estimate the concentration of contaminants house wrens along the Tittabawassee River were exposed to through their diet.
Contaminant concentrations in the tissues of house wrens were also analyzed to verify that their exposure had been characterized correctly. Specifically for the house wren, collected tissues included eggs and nestling tissues.
The health of the house wren population was assessed through the evaluation of several productivity measurements, which included nest occupancy, nest success, clutch size, hatching success, and fledgling success.
House wren data have been collected from reference areas in Sanford, Michigan, and the Pine and Chippewa rivers in and around the Chippewa Nature Center, and study areas downstream of Midland, Michigan, ranging to the Shiawassee National Wildlife Refuge and beyond to near the confluence of the Saginaw River with Saginaw Bay.
Integrating the findings from all lines of evidence provided us with the information necessary to estimate the risk of adverse effects to house wrens residing within the Tittabawassee River floodplain.