Mercury contamination in Peregrine Falcons (Falco peregrinus) in coastal Washington, 2001–2016

Abstract

Mercury (Hg) is a naturally occurring widespread and persistent contaminant globally, and its organic form is highly toxic to living organisms and is known to impact humans and wildlife. Our primary goal was to use feathers to establish a contemporary baseline of total Hg contamination levels in Peregrine Falcons (Falco peregrinus) that occur on the outer coast of Washington. We document concentrations of total Hg in feathers of 151 peregrines primarily captured on beaches from 2001 to 2016. Peregrines were captured throughout the year, with breeding and natal areas of most individuals undetermined. The bulk of our samples consisted of fourth secondary (s4) feathers, but we include fourth primary and undertail covert feathers for comparison. All s4 feather samples contained detectable concentrations of total Hg (range = 0.7–69.83 µg/g), with mean concentrations in hatch-year (HY) feathers (mean = 6.05 µg/g) significantly lower than in second-year (mean = 22.55 pg/g) and after-second-year (mean = 24.48 µg/g) feathers. We captured 23 individuals more than once to track total Hg concentrations over time (up to 12 years between first and last capture), detecting an increasing trend through their third year before stabilizing in subsequent years. All individuals first captured while in HY plumage and later recaptured (n = 20) exhibited an increased concentration of total Hg in later years (mean maximum difference over time = 25.39 µg/g). Our 16-year study illustrates widespread contamination of total Hg in peregrines captured in coastal Washington, with evidence of bioaccumulation within individuals and between age classes. Encouragingly, peregrines in HY plumage sampled during the final third of our study period exhibited a significantly lower mean total Hg concentration than the first two-thirds of our study. We detected greater total Hg concentrations in coastal Washington peregrines than in nearly all known published studies involving peregrines of various subspecies in North America and Europe, although additional research is needed to establish toxic effects levels in this species.