DDT, Chlordane, Toxaphene and PCB Residues in Newport Bay and Watershed: Assessment of Hazard to Wildlife and Human Health - Reviews of Environmental Contamination and Toxicology - page 112

Table 22 Reproduction of osprey pairs at Shellmaker Island (SI) and San Joaquin Wildlife
Sanctuary (SJWS) a
Year Site Eggs Chicks Fledglings Productivity Comments

2005 SI 2 0 0 0 First mating

2006 SI ≥ 3 3 2 2 Egg count not available

2007 SI ≥ 3 3 2 2 Egg count not available

2008 SI ≥ 3 3 3 3 Egg count not available

2009 SI ≥ 4 4 4 4 Egg count not available

2010 SI 3 3 3 3

2010 SJWS 1 1 1 1 Female SI 2008; fi rst mating

≥

2011 SI 3 3 3 3 Egg count not available

2011 SJWS ≥ 2 2 0 0 Chicks died of unknown cause;

hemorrhaging noted in lungs

2012 SI ≥ 3 3 3 3 Egg count not available

2 2 2 2 Egg count not available
a Data from Thomas ( 2010 ), Reed ( 2010 ), Reicher ( 2010 ), Kerr ( 2006 ) as well as personal communi-
cations from: Carla Navarro Woods, Reserve Manager, California Department of Fish and Game,
who provided breeding data on the osprey pair at Shellmaker Island; Scott Thomas and of the
Audubon Society, who provided breeding data for both osprey pairs; Nancy Kenyon of the Audubon
Society, who provided breeding data on the osprey pair at the San Joaquin Wildlife Sanctuary

2012 SJWS ≥

Productivity can be expressed as fl edglings per breeding attempt. With 23 fl edglings
and 11 breeding attempts, the productivity is 23/11 = 2.09 fl edglings/breeding attempt.
This high level of productivity of ospreys in Newport Bay suggests that DDT levels in
eggs are below the threshold associated with hatching failure. Because ospreys are
particularly sensitive to the most toxic effect of DDT, namely, on reproduction, they
serve as an ongoing sentinel for the potential of DDT to affect all wildlife.

Discussion and conclusions . Considering the information on the effects of DDT on
osprey reproduction that has been reviewed and summarized, can a threshold for the
action of DDE on reproduction in osprey be determined? A lot is known. However,
one is also aware of unknown exposures and the high variability of residues and
response. A wide range of endpoints and approaches can be taken.
For a given breeding area, a fi eld study, in which no signifi cant eggshell thinning
was found defi nes the known threshold for any biological effect of DDE residues in
those eggs. The threshold for that fi nding is approximately several hundred ppb
DDE. A threshold for increased shell breakage and reduced hatchability is approxi-
mately 3-4 ppm DDE. Recovery and stabilization of DDE-poisoned populations of
ospreys has been associated with DDE egg residue levels as high as 5-8 ppm.
Although postulated, toxicity has not been shown to occur for DDE residue levels
in eggs that cause shell thinning up to 10%. Thinking in evolutionary terms, normal
eggshell thickness evolved to prevent breakage during incubation, as well as to pro-
vide gaseous exchange and an appropriate degree of hydration. There is a consider-
able range in normal eggshell thickness. Neither hatching success, nor health of the
fl edgling appears to be compromised by minimal shell thinning. There is some