A study is underway to examine the effects of sea pollution on the rare Bermuda Cahow.

Two scientists at the Bermuda Biological Station for Research have started analysing abandoned and unhatched Cahow eggs and embryos.

They are looking for any signs of pesticides or PCB -- polychlorinated biphenyl, a toxic by-product of industrial processes.

The studies will be checked against a mid-1960s analysis to see whether the threat of pesticide contamination has increased or decreased.

In addition, because the Cahow sits on top of a large food chain the study could be a good indicator of the health of the ocean.

Yesterday Government's conservation officer David Wingate said about half the eggs produced by the Cahows failed due to infertility, breaks or the chick dying.

Some have been retrieved and the eggs and embryos will be used for the study of pesticides and PCBs, he said.

It is not known whether pollutants are to partly blame for the failures, but if chemicals are found it could help to explain the mortality rate.

In the mid-60s it was confirmed that the now banned chemical DDT caused egg shell thinning and breakage. Now it is thought that PCBs could have a similar effect.

"The beauty of this study is that the Cahows are long lived so we have the same pair occupying the same nest site for up to 20 years.

"There is an opportunity for long-term monitoring of a single pair of birds,'' said Dr. Wingate.

"If we find high levels of pollutants in the eggs it could help to explain some of the failures.'' The Cahows come to Bermuda to breed and usually range over a huge area of the Western Atlantic, feeding mainly in the Gulf Stream.

They sit on top of at least a five step food chain and it is felt Cahow eggs could provide an insight into the health of the ocean. Dr. Wingate said: "The Cahow egg could be an excellent sampling device for long-term changes in pollution levels in the ocean because we can sample the same bird year after year.'' Meanwhile Dr. Wingate is waiting to see if last year's hurricanes which swept along the US East Coast have affected the Cahows' numbers.

In 1989 Hurricane Hugo was suspected of causing a higher than average mortality rate among Cahows as they were swept up in the storm and carried beyond their normal feeding areas.

Last year several hurricanes took the same route as Hugo and now Dr. Wingate is waiting to see whether they will have a similar effect.

Fifty-two nesting pairs of Cahows were recorded last year -- a record number.

"The birds are not in Bermuda during the hurricane season, but where they can be affected is on the US continent and when hurricanes go through the Cahows' feeding range,'' added Dr. Wingate.

"After Hurricane Hugo there were a lot of birds missing and I suspect that Hugo was a cause.

"Last year some hurricanes took the same route as Hugo. So far the jury is still out on the effects on the Cahows,'' added Dr. Wingate.

David Wingate