Protecting bald eagles from West Nile virus

Monday , June 16, 2014 - 12:00 AM

Standard-Examiner correspondent

KAYSVILLE – Preparation has begun in northern Utah to try to prevent a recurrence of last year’s tragedy in which 86 bald eagles contracted West Nile Virus after eating grebes infected with the disease.

The toll was 82 bald eagles dead, and four afflicted birds still alive but still suffering neurological problems, meaning they can never be released back to the wild.

To prevent West Nile Virus, a mosquito-borne disease, Davis County has been spraying for mosquitoes since the first of May, according to Gary Hatch, director of the Davis County Mosquito Abatement District.

“Seeing those bald eagles with West Nile Virus was a big thing to us and a lot of people got anxious about it,” said Hatch.

Last year thousands of eared grebes came to the Great Salt Lake and gorged on brine shrimp. In late October, brine shrimp biologists reported seeing 1,200 dead grebes. In late October, bald eagles began migrating into the Great Salt Lake.

Right after Thanksgiving, there was a hard freeze, which froze up the marshes, forcing the bald eagles to start scavenging on the dead grebes, with the first dead eagle found the first week in December.

By the middle of December, all of the grebes had migrated out of Utah, but reports found they all tested positive for West Nile Virus.

To prevent a repeat of the situation, nearly 5,000 aerial mosquito larvae acres have been treated in Davis County, and just over 1,000 ground acres. Almost 180,000 adult mosquito acres have been treated aerially, with nearly 400,000 ground acres covered.

Davis County’s mosquito abatement trucks run every night, with a bike crew, wearing bright green safety shirts, who treat just under 60,000 catch basins a year. “We get called in as being terrorists putting things in catch basins, so we try and report to each city’s police department when we will be in town,” said Hatch.

Davis County also treats fish and ornamental ponds by placing free mosquito fish, which Hatch says are very effective for keeping mosquito larvae down.

Reports of grebes migrating again in Top of Utah this spring show no signs of any dead birds, so mosquito officials hope the good news will continue throughout the year.

When reports indicated the dead grebes from last winter were infected with West Nile Virus, fingers were being pointed at Utah’s mosquitoes, according to Hatch. However, all of the testing mosquito abatement did last year of mosquito pools in Davis County indicated no sign of West Nile Virus, though two chickens did test positive for the virus out in West Point, but that wouldn’t explain the large number of dead grebes.

Hatch said they worked heavily with the state and federal fish and wildlife departments, and it has been determined that the virus strain seen in the dead grebes and eagles in northern Utah last winter was related to a strain in 1999 when West Nile Virus came into New York, and grebes came with the virus into Utah.

Before the public concern of bald eagles being infected with a mosquito-borne illness, concerns were raised about the mosquito abatement pesticides and their residues affecting the honey bee mortality rate in the area.

As a result, Davis County Mosquito Abatement has taken steps to ensure the survival of local bee hives. “When we are spraying at night, bees are in their hive, therefore protected, so if we are spraying at the wrong time of night, we will kill bees,” said Hatch. “We are very conscious, making sure not to spray until the sun goes down. We are working with bee keepers in the county, making sure their bees are not exposed to the residue from our spray.”

Sign up for e-mail news updates.