Eastern Bluebird
The eastern bluebird is the least commonly encountered songbird being studied on the Tittabawassee River; however, given their magnificent blue hues, they can be easily spotted in the floodplain fields along the river. Our research aims to verify that the eastern bluebird population that resides within the Tittabawassee River floodplain is not experiencing adverse effects from site-specific contaminants, specifically dioxins and furans.
The eastern bluebird possesses many ideal attributes of a study species for assessing bioaccumulative compounds in the environment, including being obligate cavity nesters (i.e., they don’t excavate their own cavities and are dependent on natural cavities or, more importantly, nest boxes), being the only songbird species being studied to overwinter on site, having a widespread distribution, being resistant to disturbances while nesting, being limited in foraging range during nesting, and maintaining a similar home range for multiple years.
To determine their dietary exposure to contaminants, site-specific diets of the eastern bluebird are determined through the collection of bolus samples (i.e., small masses of chewed food). Bolus samples are collected from nestling birds between the ages of 3 and 12 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 eastern bluebird, this includes mostly grasshoppers, moths, caterpillars, and worms. These collections allow us to estimate the concentration of contaminants eastern bluebirds along the Tittabawassee River are exposed to through their diet.
Contaminant concentrations in the tissues of eastern bluebirds are also analyzed to verify that their exposure has been characterized correctly. Specifically for the eastern bluebird, tissues collected include nestling tissues and eggs.
The health of the eastern bluebird population is assessed through the evaluation of several productivity measurements, including nest occupancy, nest success, clutch size, hatching success, and fledgling success.
Eastern bluebird 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 eastern bluebirds residing within the Tittabawassee River floodplain.
