Some metals and metalloids in the blood of three species of shorebirds increase while foraging during two-week migratory stopover in Delaware Bay, New Jersey

Abstract

Most migratory shorebird species are declining, some are endangered, and some may be vulnerable to contaminants on long distance travel between wintering grounds and high latitude breeding grounds. We examined whether shorebirds accumulated trace elements at the Delaware Bay (New Jersey) stopover by testing the null hypothesis that there was no difference in the levels of arsenic, cadmium, chromium, lead, mercury, and selenium in blood of three species of shorebirds collected early in their stopover compared to levels in blood collected about two weeks later near the end of the stopover, before departing for breeding grounds. There were significantly higher levels of all metals and metalloids in the blood of ruddy turnstone (Arenaria interpres) later in May than earlier. There were seasonal increases in blood levels of arsenic and selenium for all three species. Chromium and lead levels also increased in red knots (Calidris canutus). These increases occurred although the birds were only present for about two weeks. Levels of arsenic, mercury, and lead in knots and selenium in sanderlings (Calidrris alba), exceeded reported effects levels. These results have potential implications for studying the refueling physiology, energetics, and feeding behavior of migratory shorebirds. However, they also suggest cause for concern because the increased contaminant loads occur in a short period, and the high metal level bolus received all in a few days may result in adverse effects.

Keywords: Arsenic; Lead; Mercury; Metals and metalloids; Migratory risk; Selenium; Short-term uptake.

Fig. 1.

Map of Delaware Bay showing the sampling sites on the New Jersey side. The insert shows the location of Delaware Bay on the Atlantic coast of North America.

Fig. 2.

Metal levels for three species of shorebirds from 2019. Each point (diamond, square or circle) represents an individual, although some overlap. The horizontal bar indicates the arithmetic mean for each species. The dotted line indicates the lowest effects levels (see discussion); the lowest effects level for cadmium is 260 ppb, and there is none for chromium. Note that the scale differs for each element, and that several squares (individuals) overlapped sometimes.

Fig. 3.

Blood levels of metals (ng/g, wet weight) in individual Red Knots captured early (n = 15) and late (n = 15) in the migration stopover at Delaware Bay, NJ. The significant changes are chi square tests for significant differences between early and late levels (p values are provided in parentheses), with the regression line. The dotted line indicates the lowest effects levels (see discussion); the lowest effects level for cadmium is 260 ppb, and there is none for chromium.

Fig. 4.

Levels of metals (ng/g, wet weight) in individual sanderlings captured early (n = 19) and late ( n = 15) in the migration stopover at Delaware Bay, NJ. The significant values are provided (Chi Square), with the regression lines. The dotted line indicates the lowest effects levels (see discussion); the lowest effects level for cadmium is 260 ppb, and there is none for chromium.

Fig. 5.

Levels of metals (ng/g, wet weight) in individual turnstones captured early (n = 25) and late (n = 20) in the migration stopover at Delaware Bay, NJ. The significant values (Chi Square) are provided, with the regression lines. The dotted line indicates the lowest effects levels (see discussion); the lowest effects level for cadmium is 260 ppb, and there is none for chromium.