Ca. Hui et al., Contaminant profiles of two species of shorebirds foraging together at twoneighboring sites in south San Francisco Bay, California, ENV MON ASS, 71(2), 2001, pp. 107-121
The San Francisco Bay estuary is used by over one million shorebirds during
spring migration and is home to several hundred thousand during the winter
. Most shorebird use occurs in the southern reach of the estuary (South Bay
). The reduced water circulation and discharge from industrial sources in t
he South Bay are responsible for the highest levels of some trace elements
in the estuary. Wintering shorebirds have been found to have strong site fi
delity to areas as small as a few kilometers in the South Bay, which may in
crease their exposure to contaminants near local point sources. In addition
, different shorebird species foraging at the same site have been shown to
have different contaminant burdens. Thus, our objectives were to test wheth
er contaminant burdens differed by species, or whether contaminant burdens
differed in shorebirds collected at adjacent sites. We examined the contami
nant profiles of two species of shorebirds, long-billed dowitchers (Limnodr
omus scolopaceus) and western sandpipers (Calidris mauri) that forage toget
her at two sites, Hayward and Newark, separated by 8 km in the South Bay. W
e used multivariate analysis of variance tests to compare the composition o
f 14 elemental analytes in their liver tissues and estimated their molar ra
tios of Hg and Se. Composite samples were used for contaminant analyses bec
ause of the small body size of the shorebirds. Seven elemental analytes (Ag
, Ba, Be, Cr, Ni, Pb, V) were below detection limits in a majority of the s
amples so statistical analyses were precluded. In the measurable analytes (
As, Cd, Cu, Hg, Mn, Se, Zn), we found no significant intra-site differences
of contaminant profiles for the two species. We pooled the samples to exam
ine inter-site differences and found significant differences in contaminant
profiles between shorebirds at the neighboring sites (P = 0.03). Shorebird
s at Newark had higher (P < 0.05) concentrations of As, Cd, and Se than tho
se at Hayward. Dowitchers at Newark had concentrations of Hg and Se which w
ere highly correlated (P < 0.003) in a mean molar ratio of 1:19, similar to
that reported in other birds. In the larger dowitcher species, we also exa
mined exposure to 20 organochlorine compounds. Organic analyses showed that
the dowitchers had been exposed to DDE, PCBs, dieldrin and trans-nonachlor
, but with no significant differences in concentrations between Hayward and
Newark (P > 0.05).