|Title||Results of the 1987 Michigan colonial waterbird monitoring project on Caspian Terns and Double-crested Cormorants: egg incubation and field studies of colony productivity, embryologic mortality and deformities|
|Year of Publication||1987|
|Authors||Kurita H, Ludwig JPinson, Ludwig M.E|
|Institution||Ecological Research Services, Inc|
|City||Ann Arbor, MI|
1. The 1987 Michigan colonial waterbird monitoring project assessed productivity and deformities by standardized field studies and incubation of eggs collected from double-crested cormorant and caspian tern colonies of Michigan. 2. Numerous deformities, some types unrecognized until now, were detected in both species. 3. Six hundred seven eggs were collected from 12 colonies with 42 archived for future residue analyses; 285 cormorant and 280 tern eggs were incubated. 4. Only 29% of cormorant and 15% of the tern eggs hatched, these low rates apparently were due to infertility and power outages that cooled incubators on at least 3 occasions. 5. Sixteen percent of 194 cormorant eggs that were incubated developed defective embryos excluding edema; 70% had either subcutaneous (head and neck) or ascites (abdominal) edema or both conditions. Embryonic mortality was associated with subcutaneous edema but not ascites. 6. Thirty-one percent of the tern eggs that were incubated developed a defective embryo. Failure of the abdominal body wall to develop (gastroschisis) was the most common defect followed by subcutaneous edema. Most defective embryos had more than one defect. 7. Cormorant eggs from Green Bay colonies and tern eggs from Saginaw Bay developed embryos with the most defects; tern eggs from central Lake Michigan and cormorant eggs from Lake Superior colonies developed embryos with the fewest defects. 8. Liver, pancreas and body size were smaller in embryos from the contaminated bay areas. Kidney areas were notably greater in cormorants from Lake Superior compared to all Lake Huron-Michigan colonies. 9. Mild ascites edema (abdominal edema) could be a normal adaptation to store water for body temperature regulation in cormorants. 10. Cormorant breeding populations in Michigan again increased dramatically (39%). 11. Cormorant clutch size and fledging rates were down slightly from 1986 to 3.16 eggs per nest and 1.81 fledglings per pair. 12. Herring Gull predation on both terns and cormorants was reduced in 1987. 13. Alewives resumed their normal place as the most important food source for cormorants in 1987; 75% of 506 food items dropped in colonies were alewives. 14. During 1987, 3,510 cormorant chicks were banded in the Michigan Great Lakes colonies and 3,757 examined for defects; seventeen hatched chicks with a defect were found for a frequency of 4.63/thousand, about one per thousand more than in 1986. 15. The field study indicated that only one in 40 cormorant embryos with a developmental defect was able to hatch. 16.Caspian tern nesting in Michigan was reduced by 4.4% to 2,720 first nesting attempts and at least 50.4% of terns nested in a new colony in 1987. 17. Some tern colonies were damaged by ring-billed gull or cormorant competition for nesting sites. Herring gull predation was generally less intense in 1987 than 1986. 18. Mean tern clutch size increased slightly in 1987, but overall Michigan colonies mean fledging rates dropped precipitously from 0.84 to 0.62 young per nest in 1987 compared to 1986. Egg fertility was much lower in 1987, especially in Saginaw Bay where 44% of eggs laid failed to develop. 19. The Saginaw Bay Confined Disposal Facility Colony failed completely in 1987 with symptoms of toxics-related chick wasting syndrome and very high rates of developmental defects in those embryos that developed. Common terns nesting on the CDF also died with the same problems. 20. The 1987 average fledging rate of Michigan Caspian Tern chicks was only 46% of the rate recorded between 1963 and 1967; clutch size and fertility were also down from historic levels. 21. Very few developmentally defective terns (about 1 in 80) aactually hatched in both the incubation and field study. 22. The wide distribution of defective tern and cormorant embryos suggests that all Michigan waters of Lakes Huron and Michigan are still significantly contaminated; aerial transport or diffusion from local hot spots may be the mechanisms that spread out the effects-causing toxics. The burst of toxic-effects problems in Saginaw Bay may be related to the 1986 flood. 23. The observed effects are consistent with described effects of PCBs, dioxins, dibenzofurans and other organochlorine toxics on other colonial waterbirds and tested domestic species. 24. The data on the two species populations studied suggest that they are sensitive effects monitors of toxicants. The status of these species should be followed using embryonic screening techniques as well as basic population analysis.