LE3 .A278 2011

2011

O'Driscoll, Nelson

Acadia University

Master of Science

Masters

Biology

Biology

Mercury contamination has been proposed as a contributing factor to the ongoing population decline of the Rusty Blackbird (Euphagus carolinus). This thesis examines mercury concentration in the species across its range to (1) identify the seasons and regions with the greatest exposure to the species, and (2) determine if mercury represents a realistic threat to the species’ health. Water and potential diet were collected from wetlands with breeding pairs in the region with the greatest mercury exposure—the Northeast—to identify those environmental mechanisms that promote the bioavailability of methylmercury (MeHg). Mercury burdens to the Rusty Blackbird were assessed using blood and flight feather samples non-lethally collected from across their winter range in the United States and from the east-west limits of their breeding range in Canada and the United States—from the Maritimes provinces and New England states and from across Alaska. Samples from breeding regions had blood mercury concentrations at least an order of magnitude greater than winter Rusty Blackbirds (0.07 μg g-1 Hg) suggesting the dominant exposure period for the species is during the spring and summer. Additionally, Rusty Blackbirds breeding in the Northeast (0.94 μg g-1 Hg) had blood mercury concentrations > 3× that of Alaskan birds (0.26 μg g-1 Hg). Feather mercury concentrations were also greatest in the far eastern breeding range (8.26 μg g-1 Hg) and were similar in all other regions (2.30 μg g-1 Hg), further implying that the Northeast has the highest mercury exposure across the species’ range. xiv Overall, both blood and feather mercury concentrations for the Northeast exceeded estimated adverse effects levels for the species (1 μg g-1 blood-Hg; 5 μg g-1 feather Hg) supporting the case for mercury as a contributing factor in the population decline for this region. Water, invertebrates, and blood from adult Rusty Blackbirds were collected at Northeastern wetlands for MeHg and total-Hg analyses, along with six additional water column parameters (dissolved organic carbon [DOC], pH, dissolved oxygen [DO2], conductivity, redox potential, and temperature). Multiple stepwise regression analyses were used to identify the water variables associated with MeHg production and bioavailability. Water variables significantly related to MeHg concentrations for eight taxa, including invertebrates and bird blood, were DO2 (mean part correlate = –0.38), pH (–0.20), and DOC (–0.20). Redox potential (part correlate = 0.76) and DO2 (–0.80) were the strongest significant parameters related to MeHg production (water %MeHg). Of four assumed prey taxa, MeHg concentrations of three were significantly correlated with bird blood-Hg concentrations: Araneae (r2 = 0.49, p = 0.03), Ephemeroptera (0.84, 0.001), and Trichoptera (0.34, 0.05), with Odonata not correlated (0.01, 0.75). An estimated MeHg biomagnification factor of 19 for breeding Rusty Blackbirds was developed using these four prey, with a bioconcentration factor from water MeHg to bird of 10 x 106. An environment having a high bioavailability of MeHg in combination with the species’ high trophic position best explains elevated Hg concentrations in this regional population. xv

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https://scholar.acadiau.ca/islandora/object/theses:168