|Abstract or Summary
- Great blue heron (Ardea herodias) eggs and prey items were collected from six colonies on the Columbia and Willamette rivers and Puget Sound during 1994-95. Contaminant concentrations, reproductive success, and biomagnification factors (BMFs) were determined and effects of residue levels were measured by H4IIE rat hepatoma and ethoxyresorufin-O-dealkylase (EROD) bioassays. Fledging and reproductive rates were similar to those determined for other healthy heron populations. With the exception of one site, mean residue concentrations in heron eggs and prey were low. However,
elevated concentrations of PCBs were detected in eggs and prey from Ross Island on the
Willamette River. Among-site differences were not statistically significant different in
H4IIE TCDD-equivalents (TCDD-EQs) or EROD activity, although the TCDD-EQ for Karlson Island was 9 to 20 times greater than that of any other site. Large differences existed between toxic equivalents calculated from egg residue concentrations and TCDDEQs, which indicated non-additive interactions among the compounds. TCDD-EQs and nest failure were positively correlated with TCDD concentration. Biomagnification factors varied greatly among sites for most compounds. Of the organochlorine pesticides,
DDE and heptachlor epoxide were magnified the most. Penta- and hexachlorinated dioxins were biomagnified to a greater extent than TCDD. Our results support the use of great blue herons as an indicator of contamination in aquatic ecosystems. Their relatively low sensitivity to organochlorine contaminants and high trophic position allows contaminant accumulation and biomagnification without immediate adverse effects which are often seen in other, more sensitive species. Breeding behavior of great blue herons was also examined at the six colonies to Patterns of brooding, pair bonding, preening, and nest visits were significantly different (P < 0.05) between the reference and non-reference sites. The site with the highest concentrations of DDE and PCBs had significantly lower nest attendance and feeding rates relative to the reference site. Differences in nest attendance among colonies were inversely correlated with DDE concentrations (r = -0.79, P = 0.06). Among-site differences in the odds ratios for adults feeding chicks were positively correlated with DDE and PCB concentrations (r = 0.84, P = 0.04 and r = 0.79, P = 0.06 respectively), but these relationships may be an artifact of the low frequency of occurrance of feeding sessions and its dependence on nest attendance. Clutch size and hatch, fledge, and reproductive success were similar to those reported for healthy populations. Differences in activity budgets among sites do not appear to be affecting reproductive rates of herons at the different colonies.