BAN: West Nile Virus (2005)

by Steve Eno

I had a few calls this season about dead bluebirds in boxes and the possibility of WNV always came up. On June 6th at Mahoney State Park I found a dead male bluebird on top of a nest with four nestlings about ten days old. The dead bluebird was in perfect condition and had probably been dead for less than 24 hours. I took the bird to the Health Department where the test for WNV came up negative. (I’m happy to report that the female bluebird was able to successfully feed the four young and they all fledged.)

I talked with Dr. Wayne Kramer, State Medical Entomologist, and asked him to give me an update on the status of WNV for this year and the possible impact this had on Eastern Bluebirds and Black- apped Chickadees. Many people in the Eastern part of the state have reported the absence of chickadees in their area in the last two years.

Thanks to Dr. Kramer for the following update on bird testing and WNV in Nebraska:

“On bluebirds and chickadees, our [State Department of Health & Human Services] testing summaries on WNV are below:

Eastern bluebird
2002: 1+ / 3 tested [1 bird tested positive out of 3 birds tested]
2003: 5+ / 7 tested
2004: 0+ / 2 tested
2005: 0+ / 1 tested (as of 7/25/05)

Black capped chickadee
2002: 1+ / 1 tested
2003: 1+ / 1 tested
2004: 0+ / 0 tested
2005: 0+ / 1 tested (as of 7/25/05)

In 2005 we have tested a total of 351 birds comprised of 39 species collected in 61 Nebraska counties. No birds have tested positive as of 7/25/05. I am quite surprised by this and we do expect some positives any day as we now have positive mosquito pools from 3 counties, 1 positive horse, and a couple of human cases that will be announced later this week.

Something definitely is happening with regards to WNV and its impacts on bird populations. Early on, this virus killed a lot of birds as witnessed by the numbers/percentage of positive rates shown below. But in 2004 and 2005, there does not seem to be as much virus activity and therefore not as much bird mortality. This is reflected in the fact that a lot of dead birds in '04 and '05 that were tested were not killed by WNV. Also it may be possible that some bird species that were previously heavily impacted (killed) are now reaching some equilibrium with the virus and not being impacted as much. The only way to confirm this would be testing live birds of these species on an ongoing basis by taking a small quantity of blood and looking for antibodies to the WNV virus to show exposure but no mortality.