West Nile Virus

Over the past two years, I’ve twice been out to visit friends in Seattle, Washington, and have really enjoyed the lush greenness of the area.  

Of course, I’m always looking for birds no matter what other activities we’re doing.  Can’t pass up the chance to see birds I’ve never seen in the wild before.  The one I most want to spot is a Golden Eagle, as they are one of my favorites, but so far no luck. 

However, what I did notice during both trips was the huge abundance of crows everywhere you go.  You can’t miss their presence, even if you’re not a bird watcher—they’re huge and noisy!  While some find the crows’ constant noise a little irritating, I found it fascinating to watch them just do what they do in the wild in a way we here in St. Louis cannot.  The difference in crow density between the two areas is likely related to West Nile virus and geography.

West Nile virus first showed up in the New York City area in 1999.  It was a new virus to the area and took a bit of time to be identified as such, likely brought into port by a foreign shipment of birds.  By September of 1999, after a rash of bird deaths, particularly crows, the New York Department of Health identified the disease based on both wild bird specimens and birds from the Bronx Zoo. 

By 2001, West Nile was all over the Eastern seaboard and the South-- particularly heavy in Florida.  Seven cases were reported in St. Louis County.  Because West Nile virus is predominantly spread by mosquitoes, it makes sense that an area like Florida with huge densities of mosquitoes would suffer greater losses. 

By 2004, there were reported cases from nearly every county in Missouri.  It had spread as far west as Idaho and Oregon, and California had been bombarded.  But no cases were reported from Washington.  Over time, West Nile did finally make its way into Washington, but only in comparatively low cases. 

By 2009 there were no cases reported in Missouri, but 10 counties reporting in Washington.  The number of bird specimens from those counties only numbered 22, as opposed to California who still reported 412 specimens in 2010. 

Fortunately, Washington’s climate has a combination of characteristics working against the spread of West Nile Virus that most places don’t.  The mountains through the middle of the state create a physical barrier against both insect movement and the movement of most birds.  Although Washington is quite wet most of the year, they rarely get the heat that helps to spawn legions of mosquitoes.  The wind patterns and frontal systems across the mountains seem to keep the air less stagnant than what we experience here in the St. Louis area in late summer--prime West Nile transmission time.  While there are likely other factors at work, these seem like plausible possibilities for Washington’s isolation from this virus.

To my knowledge, it is not understood why the Corvid family (ravens, crows, jays, & magpies) are more susceptible to West Nile mortality than other types of birds.  Crow deaths became an early indicator of West Nile in many areas; however, crows were not feared to be a vector for the spread of the disease, as they are not generally migratory. 

Fortunately, through a conscientious and sustained effort, we here at the Sanctuary were successful in keeping our birds safe during the worst of West Nile in our area.  Mosquito Magnets positioned throughout the site, an excellent resident bat population and meticulous avoidance of standing water wherever possible were key to our success.  These are all summertime mosquito deterrents we continue to employ. 

We did treat many cases of the disease in wild birds at our Wildlife Hospital, where it seemed to show up in Great Horned Owls more often than other raptor species.  The reasons for this are unknown, but one could conjecture that an animal hunting at night when the winds have died down and the mosquitoes are out in force would be at greater risk for being bitten by an infected insect.

 

Here in St. Louis and the surrounding areas, it would seem that the populations of crows and blue jays are slowly rebounding.  Some birdwatchers have told us they are seeing more Jays at their feeders after years of seeing none, where there once were many.  The sound of crows calling from our forests is a little more noticeable now after it had been conspicuously missing for a time. 

Hopefully, with time, the affected bird populations will make their way back to normal levels.  Working with crows and ravens in our shows is amazing and challenging; it has definitely increased my awareness and appreciation for their wild counterparts as well.  You never know what mischief you might catch them in next!

Information and data obtained from: http://diseasemaps.usgs.gov & http://birds.cornell.edu/westnile.htm

Submitted by Dana Lambert, World Bird Sanctuary Naturalist