Metal concentrations in the eggs of endangered Florida scrub-jays from central Florida

Abstract

We analyzed metal levels in the eggs of the endangered Florida scrub-jay (Aphelocoma coerulescens), an extremely sedentary and modestly long-lived passerine bird. Eggs were obtained as part of the long-term study of this species at the Archbold Biological Station, located in south central Florida. Following a brief and usually short dispersal, Florida scrub-jays remain in a permanent territory in their scrub oak habitat, where they feed mainly on insects and acorns. As they are low on the food chain and sedentary, we expected levels of contaminants to be comparatively low and to reflect the local environment. No significant yearly differences existed for any metal between eggs collected in 1997 (n = 11) and 1998 (n = 5). Arithmetic mean metal concentrations (whole egg, dry weight) were low for arsenic (34 ppb), cadmium (25 ppb), mercury (74 ppb), and lead (66 ppb), intermediate for chromium (226 ppb), and higher for selenium (1,470 ppb) and manganese (2,230 ppb). Except for the low mercury value, all these means were within the range of mean values reported for a wide range of nonpasserine species, including those at high trophic levels, but are lower than concentrations associated with abnormalities in birds. The three essential elements (chromium, selenium, and manganese) were approximately normally distributed, whereas arsenic, cadmium, lead, and mercury were highly skewed (arithmetic mean much higher than geometric mean).