[texbirds] West Nile strikes deep, crows extinct, jays going
- From: Joseph Kennedy <josephkennedy36@xxxxxxxxx>
- To: 4 Texbirds Maillist <texbirds@xxxxxxxxxxxxx>
- Date: Thu, 23 Aug 2012 20:33:01 -0500
West nile has struck heavily around my house. About the time the announced
the first case off to the west, I started daily counts and watches.
Crows were wiped out in this whole section of west houston in the year when
WNV first arrived here. My crows were friends but lived in 2 groups that
actually stayed well off to the west and came to visit and beg. About 5
weeks ago one group vanished over a day or so and then the others went
overnight about 3 weeks ago. Crows roost communally as family groups.
Crows take 2-3 days to die after showing symptoms, the main focus is a very
high fever. The birds try to find damp ground and lay flat with spread
wings to try and cool. Usually die near roosts which results in finding the
dead birds under the site the next morning. They do not appear to feed.
It is harder to track the jays as there are dozens coming for peanuts and
dogfood etc. Again many are still in family groups or clans and travel
together. I have felt that numbers started down after the last crows went
but last weekend I started to find sick birds on the balcony and about 2/3
of the birds are gone just a few days later.
Jay symptoms are different than crows and apparently are caused by the
disease affecting the brain. The birds lose the ability to take off but can
fly when they fall off the balcony. They can light on a branch but then
have strange difficulty turning around. Unlike crows they feed until the
last second. In other years, I have watched them fly off the balcony and
drop dead in mid-air before they reach perch. My general impression is
that the older jays died before the youngsters. Maybe differential roosting
in the clan.
While the papers talk about the disease being spread by birds, much of the
spread actually comes from person/person and much more horse to person etc.
Wide scale virus movements track human and horse migration rather than
birds.
There is little study of how birds get infected. The normal culex mosquite
lives in storm sewers etc and comes out at dusk and bites your ankles. The
jays etc roost high in trees where the bugs do not as they are not height
people and the wind up there discourages them. No studies have been done on
any of the tree top and arbo-specialist mosquito species as they local
people only do culex and possibly tiger mosquitoes. It has been posited
that some some of the rare treetop mosquitoes are super-infectors and
spread the virus among birds which then are bitten and infect the lower
down mosquitoes. No testing is even done on those species if captured in a
trap.
The culex that lives in the rockies out in the woods rather than in town is
a known super-infector species and really does a number on horses and then
people.
Note that birds with the virus are very sick. Very sick birds do not
migrate. They have to build up fat and reserves and that is hard to do when
unable to eat and having a high fever.
When I was helping do virus migration studies via birds, we never found a
single migrant with virus over 5 years with over 5,000 birds a year. We
never found any virus in the local birds after the passage of migrants.
They now know mosquitoes actually overwinter, in the case of culex in storm
drains, and that the virus can be inherited over several mosquito
generations.
People are major spreaders. Say you get bitten while birding in Dallas. You
have an 80-90% chance of not having any symptoms so you go to Sabine the
next weekend and feed some of the vast horde of mosquitoes there. They then
can infect the horses, more people, birds etc so one birder from dallas can
move the virus a few hundred miles. Many birders do not use sprays so they
are very good disease vectors.
There has been much discussion as to why some birds are heavily infected
and others not. The species can change; chickadees in Chicago get sick but
in other areas do not. There is some feeling that black plumage or the gene
that promotes black plumage may have some effect. If I remember blue jays
are black birds with feathers that appear blue. Nobody has been really
looking a this recently.
There was some feeling that bird populations can build up immunity as
surviving birds pass on a lower susceptablility. My jays and crows would
say that is not true. Likewise I have not seen any smaller number of
finches with eye diseases over the years. Some birds always survive but
some always get sick.
When WNV first came here I kicked myself for not tracking the effects on
crows. So this year when it showed up early, I started counting on regular
rounds. Found one crow about 1/2 days off of dying. There are now no crows
to count and many areas have no jays. That is not quite true as the drought
last year really killed the food crop which has not recovered yet before
acorn time etc. So they come to feeders etc where there is food but go back
home for the evening.
Most research is aimed at how to keep people from getting sick. The new
information in the papers today about kidney problems (40%) even in people
who had no symptoms is not good news. The disease has only been in the
country for a few years so that percentage is going to go up dramatically
over time. Twenty years from now the rate may actually push to 100%.
Lots of room for people to study things though.
--
Joseph C. Kennedy
on Buffalo Bayou in West Houston
Josephkennedy36@xxxxxxxxx
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