Stable-nitrogen isotope analysis of lipid-free egg yolk suggested a gradient in trophic levels of laying females, with black terns somewhat lower than herring gulls and Caspian terns, which were, in turn, lower than mew gulls (Fig.
Mew gulls and Caspian terns with higher [Delpta]15N values of their eggs also contained chlorinated hydrocarbon concentrations higher than those found in herring gull and black tern eggs.
The nesting biology of mew gulls (Larus canus) on Kennedy Lake, British Columbia, Canada: Comparison with mew gulls in northern Europe.
Also, the relationship between contaminants and trophic level, as inferred from stable-nitrogen isotope analysis ([Delta]15N), was examined in four colonial waterbird species: herring gull, mew gull (L.
Key words: black tern, Caspian tern, Great Slave Lake, herring gull, mew gull, mercury, organochlorines, selenium
Eggs of mew gull, Caspian tern, and black tern were collected in the North Arm, placed in solvent-rinsed jars, and frozen.
When she and her colleagues compared the 1984 estimates to the 1989 through 1991 surveys, population declines at oiled sites appeared to exceed those at unoiled sites among loons, harlequin ducks, scoters, black oystercatchers, Arctic terns, and mew gulls
. Among the most significant declines: Loon and scoter populations at oiled sites were 86 percent lower than expected and harlequin ducks 76 percent lower than expected.