Environmental Engineering Reference
In-Depth Information
correlation between DDE levels and shell thickness in an analysis of American
avocet eggs, although the shell thinning was not within the range that would result in
hatching failure.
The recent successful breeding of two osprey pair in Newport Bay implies that
levels of DDT in the fi sh diet of this sensitive species are nontoxic. The breeding
data are presented and discussed later in this review.
Many bird species resident to Newport Bay and Watershed have been studied in
regard to the levels and effects of DDT at other locations. A detailed review of the
effects of DDT on shell thinning and hatching success in the brown pelican, osprey,
petrels, and sparrow hawk can be found in later chapters of this review, where effects
from DDT in these species played a central role in establishing guidance levels for fi sh
and water. The endangered species, the Belding's savannah sparrow and California
gnatcatcher, are not known to be sensitive to the reproductive effects of DDT, most
likely because these species feed in a food chain with a relatively low potential for
bioaccumulation. The American coot (
Fulica americana
), eating mostly a vegetable
diet, would also not be expected to be sensitive to the reproductive effects of DDT.
The peregrine falcon is highly sensitive to the reproductive effects of DDT when
consuming birds feeding in an aquatic environment. However, the lack of nesting sites
(remote rock cliffs) proximate to Newport Bay and Watershed would preclude this
food pathway. A possible exception is nesting on bridges and buildings. The following
is a review of representative scientifi c studies of the levels in and effects of DDT on
some additional bird species found in Newport Bay and Watershed.
DDT and Terns
. There are many reports on DDT levels in tern eggs as well as
associated measures of eggshell thickness, hatching success and productivity. Data
from Forster's tern, common tern, Caspian tern and least tern are summarized below.
The terns are closely related, providing a measure of susceptibility to DDT effects
on reproduction for the genus and for the threatened tern species, the least tern.
King et al. (
1991
) measured DDE levels, eggshell thickness, and hatching success
in Forster's tern (
Sterna forsteri
) eggs from two Texas bays. Seventy-one eggs were
analyzed for DDE. One egg was taken per nest. Hatching success was monitored in
the remaining eggs. DDE levels in eggs ranged from 0.1 to 9.0 ppm. The geometric
mean concentrations of DDE in eggs from the two bays were 0.8 and 1.6 ppm.
No correlation was found between the level of DDE in eggs and eggshell thickness
or hatching success.
Ohlendorf et al. (
1988
) measured DDT levels in ten Forster's tern eggs from Bair
Island in San Francisco Bay. The geometric mean concentration of DDT (all DDE)
was 1.92 ppm with a range of 0.88-7.1 ppm. DDE levels were not correlated with
eggshell thickness.
Vermeer and Reynolds (
1970
) reported DDE levels ranging from 2.0 to 25.2 ppm
in ten egg composites from common terns (
Sterna hirundo
) in Central Canada in
1968-1969 at the height of the DDT era.
Switzer et al. (
1971
) reported a mean DDE level of 7.57 ppm in 68 eggs collected
from a common tern colony in Alberta, Canada in 1969. DDE levels ranged from
0.64 to 104 ppm. Productivity of the colony was very low, but the authors found no
correlation between DDE egg levels and eggshell thickness. A follow-up study in
Search WWH ::
Custom Search