Eastern Bluebird (Sialia sialis)
The eastern bluebird is the least commonly encountered songbird that was 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 aimed to verify that the eastern bluebird populations that reside within the Tittabawassee River floodplain were not experiencing adverse effects from site-specific contaminants, in particular, 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, for this study, artificial 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 define their dietary exposure to contaminants, site-specific diets of the eastern bluebird were determined through the collection of bolus samples (i.e., small masses of chewed prey items). Bolus samples were 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 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 eastern bluebird, these prey items included mostly grasshoppers, moths, caterpillars, and worms. These collections allowed us to estimate the concentration of contaminants eastern bluebirds along the Tittabawassee River were exposed to through their diet.
Contaminant concentrations in the tissues of eastern bluebirds were also analyzed to verify that their exposure had been characterized correctly. Specifically for the eastern bluebird, tissues collected included eggs and nestling tissues.
The health of the eastern bluebird population was assessed through the evaluation of several productivity measurements, which included 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, 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 eastern bluebirds residing within the Tittabawassee River floodplain.