House Wren

The house wren is the most commonly encountered songbird being 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 aims to verify that the house wren population that resides within the Tittabawassee River floodplain is not experiencing adverse effects from site-specific contaminants, specifically 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 determine their dietary exposure to contaminants, site-specific diets of the house wren are determined through the collection of bolus samples. Bolus samples are 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 is left in place for 30 to 45 minutes, after which the samples are collected and devices removed. The site-specific dietary composition is then determined by identifying the individual insects represented. These prey items are then collected from the study area by the research team and analyzed for contaminant concentrations. For the house wren, this includes mostly moths, caterpillars, grasshoppers, and spiders. These collections allow us to estimate the concentration of contaminants house wrens along the Tittabawassee River are exposed to through their diet.

Contaminant concentrations in the tissues of house wrens are also analyzed to verify that their exposure has been characterized correctly. Specifically for the house wren, tissues collected include nestling tissues and eggs.

The health of the house wren population is assessed through the evaluation of several productivity measurements, including 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 to 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 will provide us with the information necessary to estimate the risk of adverse effects to house wrens residing within the Tittabawassee River floodplain.