Great Blue Heron (Ardea herodias)
The great blue heron is a commonly encountered resident species of the Tittabawassee River, often seen stalking its prey through shallow waters along the riverbank. Our research aimed to verify that the great blue heron populations that reside within the Tittabawassee River floodplain were not experiencing adverse effects from site-specific contaminants, in particular, dioxins and furans.
Great blue herons possess many ideal attributes of a study species for assessing bioaccumulative compounds in the environment, including being located near the top of the aquatic food web, being a long-lived species, having a widespread distribution, and displaying territorial foraging behavior.
To define their dietary exposure to contaminants, site-specific diets of the great blue heron were determined through the collection of prey remains and observations of foraging behavior. Observed prey items were then collected from the study area and analyzed for contaminant concentrations. For the great blue heron, this included fish, crayfish and amphibians. These collections allowed us to estimate the concentration of contaminants great blue herons along the Tittabawassee River were exposed to through their diet.
Contaminant concentrations in the tissues of great blue herons were also analyzed to verify that their exposure had been characterized correctly. Specifically for the great blue heron, collected tissues included eggs, nestling tissues, and adult and nestling blood plasma.
The health of great blue heron populations was assessed through the evaluation of productivity measurements, which included nest success, clutch size, and fledgling success.
Great blue heron 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.
Integrating the findings from all lines of evidence provided us with the information necessary to estimate the risk of adverse effects to great blue herons residing within the Tittabawassee River floodplain.