MERCURY AND CAUSE OF DEATH IN GREAT WHITE HERONS

Mercury contamination is suspected to adversely affect wading birds in southern Florida. To determine the magnitude of contamination associa ted with cause of death we followed 3 adult and 19 juvenile radio-tagg ed great white herons (Ardea herodias occidentalis), recovered them so on after death, and determined liver mercury content and cause of deat h. Birds that died from acute causes had less (P < 0.001) mercury in t heir livers (geometric xBAR [GM] = 1.77 ppm wet mass [wm], range 0.6-4 .0 ppm, n = 9) than did those that died of chronic, often multiple, di sease (GM = 9.76 ppm, range 2.9-59.4 ppm, n = 13). Juvenile herons tha t migrated to mainland Florida accumulated more (P = 0.009) mercury in their livers than those that did not migrate. Kidney disease and gout were present in birds that died with > 25 ppm wm liver mercury. Altho ugh detrimental to the health of wading birds, mercury contamination i s presumably more determental to their reproductive efforts; therefore , an understanding of its ill effects is important in the management o f these birds.