Understanding temporal changes in contaminant levels in coastal environments requires comparing levels of contaminants from the same species from different time periods, particularly if species are declining. Several species of shorebirds migrating through Delaware Bay have declined from the 1980s to the present. To evaluate some contaminants as cause for the declines, we examine levels of mercury, lead, cadmium, arsenic, chromium and selenium in feathers of red knot (Calidris canutus, N = 46 individuals), semipalmated sandpiper (Calidris pusilla, N = 70) and sanderling (Calidris alba, N = 32) migrating through Delaware Bay, New Jersey, USA, from 1991 to 1992 (N = 40), 1995 (N = 28), and 2011–2012 (N = 80) to determine if levels have changed. We found: (1) arsenic, chromium, and lead increased in red knot and decreased in semipalmated sandpiper; (2) cadmium decreased in semipalmated sandpipers; (3) mercury decreased in red knot and sanderlings; (4) selenium decreased in red knot and increased in semipalmated sandpipers. In 2011/2012 there were significant interspecific differences for arsenic, mercury and selenium. Except for selenium, the element levels were well below levels reported for feathers of other species. The levels in feathers in red knots, sanderling, and semipalmated sandpipers from Delaware Bay in 2011/2012 were well below levels in feathers that are associated with effect levels, except for selenium. Selenium levels ranged from 3.0 µg·g⁻¹ dry weight to 5.8 µg·g⁻¹ (semipalmated sandpiper), within the range known to cause adverse effects, suggesting the need for further examination of selenium levels in birds. The levels of all elements were well below those reported for other marine species, except for selenium, which was near levels suggesting possible toxic effects.

It is essential to understand contaminant exposure and to compare levels of contaminants in organisms at different ages to determine if there is bioaccumulation, and to compare levels encountered in different geographical areas. In this paper, we report levels of mercury, lead, cadmium, cobalt, arsenic and selenium in the blood of semipalmated sandpipers (Calidris pusilla) wintering in Suriname as a function of age, and compare them to blood levels in northbound migrants at a stopover in Delaware Bay, New Jersey. We found (1) young birds had higher levels of cadmium, cobalt, and lead than adults (after second year birds); (2) there were no age-related differences for arsenic, mercury and selenium; (3) only four of the possible 16 inter-metal correlations were significant, at the 0.05 level; (4) the highest correlation was between cadmium and lead (Kendall tau = 0.37); and (5) the adult sandpipers had significantly higher levels of cadmium, mercury and selenium in Suriname than in New Jersey, while the New Jersey birds had significantly higher levels of arsenic. Suriname samples were obtained in April, after both age classes had spent the winter in Suriname, which suggests that sandpipers are accumulating higher levels of trace elements in Suriname than in Delaware Bay. The levels of selenium may be within a range of concern for adverse effects, but little is known about adverse effect levels of trace elements in the blood of wild birds.

Understanding the relationship between metal level in predators and their prey is an important issue, and is usually difficult to determine because animals eat a variety of organisms. However, shorebirds that stop over during spring migration along Delaware Bay (New Jersey) stay for only 2–3 weeks, and eat mainly horseshoe crab (Limulus polyphemus) eggs. In this paper, we examine the relationship between metal levels in horseshoe crab eggs, and blood and feather levels of metals in red knot (Calidris canutus rufa; n = 30), sanderling (Calidris alba; n = 20) and semipalmated sandpiper (Calidris pusilla; n = 38) from Delaware Bay. There is a rich literature on metal levels in feathers. For all three species, the levels of arsenic, cadmium, chromium, lead and mercury in blood were highly correlated with the levels of metals in the eggs of horseshoe crab (17 pooled samples). This indicates that the levels in the blood of these shorebirds quickly reflect levels in their prey (horseshoe crab eggs), while metals in the feathers were not correlated with the levels in eggs. Semipalmated sandpipers had the lowest levels of arsenic in blood and the highest levels of arsenic in feathers, compared to the other species. At Delaware Bay, semipalmated sandpipers have a diet higher in marsh invertebrates than the other species, which may account for the differences. The levels of cadmium and chromium in blood were significantly higher in knots than other species; knots only ate horseshoe crab eggs. For all of the metals except arsenic, the ratio of levels in blood/feathers was similar among species. For arsenic, the ratio of levels in blood/feathers were significantly lower in semipalmated sandpipers than in the other species, by an order of magnitude.

Understanding the relationship between heavy metal and selenium levels in biota and their foods is important, but often difficult to determine because animals eat a variety of organisms. Yet such information is critical to managing species populations, ecological integrity, and risk to receptors (including humans) from consumption of certain prey. We examine levels of cadmium, lead, mercury, and selenium in biota from Delaware Bay (New Jersey, USA) to begin construction of a “springtime” food web that focuses on shorebirds. Horseshoe crab (Limulus polyphemus) eggs are one of the key components at the base of the food web, and crab spawning in spring provides a food resource supporting a massive stopover of shorebirds. Fish and other biota also forage on the crab eggs, and a complex food web leads directly to top-level predators such as bluefish (Pomatomus saltatrix) and striped bass (Morone saxatilis), both of which are consumed by egrets, eagles, ospreys (Pandion haliaetus), and humans. Metal levels in tissues were generally similar in algae, invertebrates, and small fish, and these were similar to those in blood of shorebirds (but not feathers). There was a significant direct relationship between the levels of metals in eggs of horseshoe crabs and mean metal levels in the blood of four species of shorebirds. Metal levels in shorebird feathers were higher than those in blood (except for selenium), reflecting sequestration of metals in feathers during their formation. Levels in feathers of laughing gulls (Leucophaeus atricilla) were similar to those in feathers of shorebirds (except for selenium). Selenium bears special mention as levels were significantly higher in the blood of all shorebird species than in other species in the food web, and were similar to levels in their feathers. Levels of metals in bluefish and striped bass were similar or higher than those found in the blood of shorebirds (except for selenium). The mean levels of cadmium, lead, and mercury in the blood and feathers of shorebirds were below any effect levels, but selenium levels in the blood and feathers of shorebirds were higher than the sublethal effect levels for birds. This is a cause for concern, and warrants further examination.