Unalaska, AK – Rat Island may almost be considered rat-free, but spreading 50 tons of poisoned rat bait over the 6,871-acre Aleutian island might have had unintended consequences. When seven U.S. Fish and Wildlife biologists returned to the area this summer they didn't find any live rats, but they did find 186 dead glaucous-winged gulls and 41 dead bald eagles.

Fish and Wildlife spokesperson Bruce Woods said the bird die-off is uncommonly high, but they can't say for sure if it was linked to the rodenticide, which in total only contained 2.5 pounds of active poison. The biologists sent samples of both the gulls and the eagles to labs for testing to determine the cause of death.

"The bird carcasses have all been used to produce tissue samples to go to the lab and then the remaining carcasses have been destroyed to eliminate any further possibility of contamination, if the rodenticide is implicated in this die-off," Woods said.

Neither the eagles nor the gulls commonly eat live rats but both scavenge for dead meat.

Woods said that the poison pellets spread on the island last fall have been used to eradicate rats on other islands around the world and have not had this effect before. He said they tested the poison in the Aleutians, as well, before using it on Rat Island.

"And we did do some preliminary testing of our own on some of the smaller islands off Adak and in that testing we determined, by radio tagging rats, that over 80 percent of the rats died underground, in their holes, and we have no eagle deaths those tests either."

Woods said the bald eagle and glaucous-wing gull populations are healthy in the region. Biologists have seen nearly 1,000 gulls near and on the island. Only the juvenile bald eagle population seems lower than average. All of the other bird species are present in average or larger numbers than in previous years.

The Fish and Wildlife Service worked with the Nature Conservancy and Island Conservation on the $2.5 million project to eradicate the rats and allow birds to re-populate the island. The rats jumped from a sinking Japanese ship onto the island more than 220 years ago and quickly took over the entire area, feasting on bird eggs and young.

Biologists will stay on the island to study the bird nesting success and to look for more evidence of rats.

"As the birds nest that will be another period when, if there are any rats present, they might become more visible. Because rats prey on bird eggs and on immature birds."

The biologists are also taking water, soil, and bird scat samples to test for further presence of the poison.