Metal levels in feathers of 12 species of seabirds from Midway Atoll in the northern Pacific Ocean

Abstract

Seabirds are excellent subjects for examination of heavy metals because they are long-lived, feed at different distances from land, and exhibit different trophic levels. In this paper we compare the levels of lead, cadmium, mercury arsenic, chromium, manganese, selenium, and tin in the feathers of birds nesting on Midway Atoll in the northern Pacific Ocean. We test the null hypothesis that there are no interspecific differences in the levels of metals in the feathers of the adult black-footed albatross (Diomedea nigripes), Laysan albatross (Diomedea immutabilis), red-footed booby (Sula sula), great frigatebird (Fregata minor), Bonin petrel (Pterodroma hypoleuca), Christmas shearwater (Puffinus nativitatis), red-tailed tropicbird (Phaethon rubricauda), wedge-tailed shearwater (Puffinus pacificus), brown noddy (Anous stolidus), sooty tern (Sterna fuscata), grey-backed tern (Sterna lunata), and white tern (Gygis alba), and young of some of these species. There were interspecific differences in the levels of all metals for adults. Christmas shearwater had the highest levels of lead, cadmium, selenium and manganese, but the second lowest levels of mercury. In general, metal levels were the lowest in the smallest species (white tern), but were not the highest in the largest species (black-footed albatross), except for manganese, arsenic and mercury. There was a high variance in metal levels among adults for some species, but not for others. White tern adults were variable for lead, while Christmas shearwaters were variable for lead and cadmium. Compared to the means for metals in other birds generally (after Burger, 1993), Christmas shearwaters had higher levels of lead, white terns, brown noddy, Christmas shearwater, frigatebirds and Laysan albatrosses had higher levels of cadmium, and bonin petrel, wedge-tailed shearwater, tropicbirds, frigatebirds, red-footed boobies, and both albatrosses had higher levels of mercury. Whereas the means for lead and cadmium were below the known effects levels, some individuals had levels high enough to cause adverse effects in the birds. The mean values for mercury in Bonin petrel, red-tailed tropicbird, and black-footed albatross were higher than the levels known to cause adverse reproductive and behavioral effects.

Introduction

There is considerable concern about the levels of heavy metals in organisms and their ecosystems, particularly species at higher trophic levels subject to bioaccumulation. While anthropogenic contaminants from urban, industrial and agricultural runoff are a major issue, levels are augmented by natural geological processes (Mailman, 1980). Global transport and deposition is an important source of mercury for many ecosystems, including the ocean (Fitzgerald, 1989).

Seabirds are particularly vulnerable to contaminants because they are long-lived and are often at the top of their food chains (Hunter and Johnson, 1982, van Straalen and Ernst, 1991, Burger et al., 1992, Burger et al., 1994). Because they are often top trophic level carnivores, seabirds have been used as bioindicators of environmental contaminants (Monteiro and Furness, 1995, Lewis and Furness, 1993).

There is a need for data on the same species in a wide range of geographical areas and for data comparing many different species representing different trophic levels from the same general area. Each approach provides useful information.

Feathers are useful indicators of heavy metal contamination because birds sequester heavy metals in their feathers, and the proportion of the body burden that is in feathers is relatively constant for any metal (Burger, 1993). For some bird species a relatively high proportion of the body burden of certain metals is in the feathers (Burger, 1993). Monteiro et al. (1998) showed that there is a high correlation between the levels of mercury in the diet of seabirds, and the levels in feathers, thus seabirds can be used as indicators of food chain effects.

In this paper we compare the levels of metals in the feathers of twelve seabird species nesting on Midway Island in the northern Pacific Ocean. For all species we present levels for feathers of adults. Young birds were available for only six species. We test the null hypothesis that there were no differences in metal levels in feathers as a function of age, size, and trophic level position. We predicted that: (1) larger birds would have higher levels of metals, consistent with their generally longer life; and (2) birds at higher trophic levels would have higher levels than those that are lower, because of bioamphlification. We were particularly interested in whether the levels of metals in feathers from the birds at Midway were similar to those known to be associated with behavioral deficits or lowered reproductive success in laboratory studies.

Although the means and standard errors for the metals, except tin, have been presented elsewhere for some species (Burger and Gochfeld, 2000a, Gochfeld et al., 1999), the following information is presented for the first time: (1) levels of tin for 12 seabird species; (2) ranges for all metals in all species; and (3) metal concentrations for red-footed booby (Sula sula) and great frigatebird (Fregata minor). Furthermore, by presenting the metals for all species in one place it is possible to examine the trophic level relationships.