Below is the abstract from an article in today's issue of the journal
Nature. Most readers will remember the arrival of the mosquito-borne
West Nile virus eight years ago in the US (a gift from Uganda,
apparently), and predictions of its effects on our birds. The Washington
Post has an article treating this study of Breeding Bird Survey data on
20 representative North American species, intended to measure the
possible effect of this virus on populations of common birds. Here are
some highlights.
        Thirteen of the 20 species seemed unaffected, but over the period since
the virus arrived, Carolina chickadees were down 68% in Maryland and 50%
in Virginia from projected levels. American crows have lost up to 45% of
their numbers in some areas, 100% in others.  Eastern bluebirds are down
by 44%. Maryland robins suffered a 32% loss. Titmice took a big hit.
House wrens and blue jays, however, seem to have recovered their lost
numbers. BBS numbers are of course limited; they are less reliable in
assessing numbers of waterfowl, nocturnal migrants, and raptors,for
example.
        My own subjective impressions over this eight years generally match
these results in Ohio: chickadees and titmice seem down; crows seem
down; wrens and jays were down, but seem to have rebounded. I haven't
noticed an impact on robin numbers, and I am just not familiar enough
with bluebird populations to say one way or another; no doubt others are.
        The Nature article also discusses the ill effects that changes in
certain bird populations may have on the larger ecosystem.  If you don't
subscribe to Nature, a good library will. This is all part of the
Floridization of our part of the world, resulting from introduced
pathogens, exotic species, and other pests. There seems to be very
little we can easily do about it.
Bill Whan


"Nature advance online publication 16 May 2007  doi:10.1038/nature05829;
Received 8 November 2006; Accepted 11 April 2007; Published online 16
May 2007
"Nature advance online publication 16 May 2007 |
doi:10.1038/nature05829; Received 8 November 2006; Accepted 11 April
2007; Published online 16 May 2007

West Nile virus emergence and large-scale declines of North American
bird populations

Shannon L. LaDeau, A. Marm Kilpatrick & Peter P. Marra1

    1. Smithsonian Migratory Bird Center, National Zoological Park,
Washington DC 20008, USA
    2. Consortium for Conservation Medicine, New York, New York 10001, USA

Correspondence to: Shannon L. LaDeau1 Correspondence and requests for
materials should be addressed to S.L.L. (Email: [log in to unmask]).
Top of page

Emerging infectious diseases present a formidable challenge to the
conservation of native species in the twenty-first century. Diseases
caused by introduced pathogens have had large impacts on species
abundances, including the American chestnut, Hawaiian bird species and
many amphibians. Changes in host population sizes can lead to marked
shifts in community composition and ecosystem functioning. However,
identifying the impacts of an introduced disease and distinguishing it
from other forces that influence population dynamics (for example,
climate) is challenging and requires abundance data that extend before
and after the introduction. Here we use 26 yr of Breeding Bird Survey
(BBS)8 data to determine the impact of West Nile virus (WNV) on 20
potential avian hosts across North America. We demonstrate significant
changes in population trajectories for seven species from four families
that concur with a priori predictions and the spatio-temporal intensity
of pathogen transmission. The American crow population declined by up to
45% since WNV arrival, and only two of the seven species with documented
impact recovered to pre-WNV levels by 2005. Our findings demonstrate the
potential impacts of an invasive species on a diverse faunal assemblage
across broad geographical scales, and underscore the complexity of
subsequent community response."

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