Investigations of heavy metals in Common Tern populations

In investigating the possible causes of the low hatchability observed in colonies of the Common Tern (Sterna hirundo) and other aquatic birds breeding in Lake Ontario, we have analyzed adult body tissues of Common Terns from Hamilton Harbour for nine of the heavy metals (Ag, Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn).For comparison, adult body tissues of Common Terns from Great Gull Island in Long Island Sound, where hatching success has consistently been higher than 90%, were also examined for these metals.No significant differences in the connections of any of these metals were found in the tissues; mercury levels reported in other studies of Common Tern eggs from Hamilton Harbour were considerably higher than those found in eggs from Long Island Sound, but were equivalent to levels in eggs from a colony in northwestern Ontario reported to have normal fledging success.It is unlikely that the metals examined are the primary cause of embryonic mortality or other factors which lower hatching success of the Hamilton Harbour colony.