Abstract
Research investigating the threat of mercury to south Florida's passerine species is essential for effective management and conservation. To date, studies of mercury in south Florida's avian species focus exclusively on piscivores, thereby ignoring passerines. I investigated mercury accumulation in three species of blackbird (family Icteridae) residing in Big Cypress National Preserve Florida (BCNP). Blood and feather samples were collected from Red-winged Blackbirds (Agelaius phoeniceus), Common Grackles (Quiscalus quiscula), and Boat-tailed Grackles (Quiscalus major). Feather mercury analysis results showed the average feather mercury concentration of male Redwinged Blackbirds (5 .09 ± 3.43 mg/kg) was above the lowest observable adverse effects benchmark of 5 mg/kg. Results also showed significant spatia-temporal, age-specific, and seasonal differences in blood and feather mercury concentrations. Feather mercury concentrations were significantly lower in Common Grackles sampled in northern BCNP during 2008 (0.32 ± 0.14 mg/kg) compared to southern BCNP during 2009 (3.75 ± 3.42). Feather mercury concentrations in young male Red-winged Blackbirds (young: 3.08 ± 3.1 1 mg/kg) were significantly lower than in adults. Blood mercury concentrations in breeding Red-winged Blackbirds (0.37 ± 0.17 mg/kg) were significantly higher compared to nonbreeding individuals (0.19 ± 0. I 3 mg/kg). The differences observed in Red-winged Blackbirds may be due to seasonal shifts in diet and habitat and indicate that lite-history characteristics influence mercury accumulation in passerines. The results of my study confirm that south Florida blackbirds are accumulating mercury, and mercury may be a threat to south Florida's endangered and threatened passerine species. My study highlights the need for comprehensive mercury research investigating passerine species.