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eggshell thinning, and productivity. DDE residues in osprey eggs had declined to
1.4 ppm with an associated eggshell thinning of 7% in the more contaminated
Delaware Bay area. The authors concluded that “PCBs and DDE in osprey eggs
were below levels considered to be toxic to egg development.” Fish were collected
in the same manner as in 1989. Total DDT residues in fi sh for the Delaware Bay
averaged 0.23 ppm. Biomagnifi cation factors from fi sh to eggs ranged from 9 to 11.
Osprey productivity increased to 1.1 young per nest in the period from 1994 to
1998. Availability of nest structures and owl predation were thought to be limiting
the population of ospreys in the Delaware Bay area.
In
2003
, Martin et al. reported on ospreys in Great Lakes Canada. The study was
conducted in 1991-1995. DDE levels averaged 1.3-2.9 ppm in fi ve study areas.
A few eggs exceeded the 4.2 ppm (15% eggshell thinning) threshold, suggesting
that reproduction in a few individual ospreys was affected. The authors concluded,
however, “…ospreys now appear to be relatively unaffected by current low levels of
chlorinated hydrocarbon contaminants.”
Henny et al. (
2003
) reported on a detailed 1993 study of bioaccumulation of
DDE from fi sh to osprey eggs in Oregon. The number of breeding pairs along the
Willamette River increased from 13, in 1976, to 78, in 1993 and 234 in 2001. Overall
productivity was 1.67 young per active nest. The geometric mean of DDE egg resi-
dues was 2.3 ppm. Two of the ten eggs analyzed had levels of DDE that would be
expected, based on other studies, to have reduced hatching success as a result of
cracked shells.
The median level of DDE in the major food fi sh for ospreys, the largescale
sucker, was found to be only 0.022 ppm. This very low fi sh residue resulted in a
bioaccumulation factor for fi sh to osprey eggs of 87, prompting the authors to sug-
gest that ospreys received signifi cant exposures during winter migration to southern
Mexico and Central America. This idea was reinforced by lower than expected bio-
accumulation of PCBs and unexpectedly high levels of DDT in some eggs. However,
much higher levels of DDE in largescale suckers from the Willamette River have
been reported. A single composite collected between 1996 and 1998 contained
0.835 ppm (US EPA Region X
2006
). A bioaccumulation factor from this fi sh resi-
due value would be 2.3/0.835 = 2.8.
In a chapter in Raptors Worldwide, Henny et al. (
2004
) described a study of the
effects of DDE residues on osprey eggshells and reproduction at nest sites along the
Columbia River in northwestern United States. The number of ospreys had been
increasing with each survey through 1998. Mean productivity was 1.64 young per
active nest (Table
21
). Eggs were collected in 1997 and 1998.
Dividing the nests into three classes by DDE egg residue level indicates a dose-
response for thinning of eggshells and impairment of reproduction. Even at
these high levels, with measurable impacts, the osprey population continues to grow.
The geometric mean residue of DDE in eggs from nests along the Columbia River
was 4.9 ppm, a value higher than residues reported by the same authors for eggs
collected in 1993 along the adjoining Willamette River. These residues are the high-
est reported nationwide for osprey eggs during the late 1980s and 1990s. Henny
et al. suggested the possibility of exposure to DDT on the wintering grounds in
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