Mercury levels in seabirds from the Azores, Mid-North Atlantic Ocean

Abstract

Levels of total mercury were determined in body feathers of 257 seabirds belonging to seven species from the Azores Archipelago, Mid-North Atlantic Ocean. Mercury levels in adult birds showed highly significant inter-specific variations. Median levels were higher in small petrels (Madeiran storm petrel=12.5 μg/g; Bulwer's petrel=22.1 μg/g) than in shearwaters (Little shearwater=2.1 μg/g; Cory's shearwater=6.0 μg/g) and terns (Roseate tern=2.0 μg/g; Common tern=2.3 μg/g). Such inter-specific variability is discussed in relation to biological factors that may influence mercury dynamics in birds. Intra-specific variations in mercury levels were also found. Mercury levels were significantly lower in chicks than in adults of Cory's shearwater, Roseate tern and Common tern. The levels in chick feathers were 60–70% of those in adult feathers. In Cory's shearwater and the terns (Roseate and Common combined), mercury levels decreased significantly with increasing age of chicks. Mercury levels in adult Madeiran storm petrel showed pronounced seasonal variation, being about 50% lower in Spring breeders than in Autumn breeders. Mercury levels are compared with levels reported for seabird populations of the same or related species, from a variety of regions. The use of bird feathers to monitor mercury in the marine environment is briefly discussed.