West Nile Virus continues to kill grouse

by Cat Urbigkit

USGS National Wildlife Health Center Director Leslie Dierauf of Madison, Wisc., issued a wildlife health bulletin last week on West Nile Virus in Greater Sage Grouse.

Since July 2006, greater sage-grouse deaths from West Nile virus have been reported in Oregon, Colorado, Idaho, Nevada, Montana, South Dakota, North Dakota and Wyoming.

WNV has now been detected in sage grouse in California, Colorado, Idaho, Montana, Nevada, Oregon, North Dakota, South Dakota, Utah and Wyoming, as well as Alberta, Canada. Experimental studies at the USDA National Wildlife Research Center have shown that WNV is usually fatal to sage grouse, resulting in death within six days of infection.

Although most cases of grouse death due to WNV are reported as sporadic incidents involving a few birds, that wasn’t the case this year in Oregon.

In August, a landowner near Burns Junction, Ore., reported seeing dead sage-grouse, resulting in the Oregon Department of Fish and Wildlife and USGS biologists investigating the mortality event. They found three fresh sage-grouse carcasses, one sick northern harrier, and more than 60 decomposed remains of sage-grouse.

A similar incident was reported along the Idaho/Nevada border at the Duck Valley Indian Reservation. One sage grouse tested positive from the Nevada side of the Duck Valley Indian Reservation. A total of 25 dead sage grouse on the Duck Valley Reservation and about 30 in Owyhee County were found by wildlife officials. Landowners and hunters also reported seeing unusual numbers of dead sage grouse in Owyhee County, and all sage-grouse hunting was closed on the Duck Valley Indian Reservation and most of Owyhee County until the impact of WNV on the sage-grouse population is better known, according to the NWHC bulletin.

In the Powder River Basin of Montana and Wyoming, research conducted by David Naugle of the University of Montana confirmed that WNV killed radio-marked sage grouse for the fourth year in a row.

Of 11 Powder River birds tested so far, five were positive for WNV and another six dead birds are being tested currently. In 2003, about 25 percent of the radio-marked sage-grouse in the Powder River Basin died from WNV. With cool summers in 2004 and 2005, that number dropped to 10 percent and 2 percent, respectively. The hot summer in 2006 was accompanied by increased mortality.

A significant increase in sage grouse mortality (16 of 67 with radio transmitters) was also reported by biologists at the Charles M. Russell National Wildlife Refuge in north central Montana. While WNV was not confirmed, north central Montana was one of the sites that experienced high female sage-grouse mortality due to WNV in 2003, according to the bulletin.

The NWHC recommended that those handling dead birds should take at least minimal precautions. Anyone who encounters a dead bird and is unsure of why it died should wear protective gloves when handling it, or use an inverted plastic bag to collect the bird. Anyone cleaning wild game should wear disposable latex gloves or similar protective alternative. Cooking meat, including game, to over 170 degrees F will kill any viruses present in the meat.