Laura Erickson's For the Birds

Birds in the News: West Nile Virus

Now that it’s October, West Nile Virus is once again rearing its ugly head. Since the disease first appeared in America in 1999, 625 people have died from the disease. So far this year, the human death toll is 59, including 2 in Minnesota and 1 in Wisconsin.

As bad as West Nile Virus is for humans, it’s even worse for birds. Most of us have probably already been exposed to the virus and developed immunity. Fewer than 5% of people who are infected with the virus get sick at all, and of them, most get only minor flu symptoms. The people most vulnerable are those with immune system deficiencies, and so it’s very important to protect ourselves and especially the very old and the very young and people who’ve been sick from mosquito bites. We can go to a store and buy repellants, and we live in houses that can be fairly effectively closed off from insects.

Birds are helpless to defend themselves against biting insects, and are far more vulnerable to this disease than we are. 99 – 100% of all crows exposed to the virus not only get sick—they die. Great Horned Owls, Red-tailed Hawks, Blue Jays, and chickadees are other species that are extremely susceptible to the disease.

So it’s very disheartening to learn that the disease has now reached the Hawaiian islands. A dead sparrow found in Kahului on Maui tested positive in a preliminary test on September 24, and the test result has now been confirmed. Mosquitoes are not native to Hawaii, and after they were introduced there in the 1800, a great many birds, as well as native humans, who had never before been subjected to mosquito-borne diseases died. Now virtually all native Hawaiian birds live at elevations above where mosquitoes reach. But with oceanic temperatures rising, mosquitoes are reaching higher heights, and many scientists fear it’s only a matter of time before virtually all native Hawaiian birds become extinct. Hawaiian state health and wildlife officials have said they are particularly concerned about West Nile coming here because the state’s temperate climate could allow for year-round transmission of the disease. In addition to its impact on residents, they have warned, the disease could also devastate Hawaii’s native bird populations.

American Crow counts fell to a 15-year low in the Midwest on Christmas Bird Counts for 2002-2003, and in Ithaca, New York, where the disease first appeared in 1999, the crow population has been decimated. That particular local crow population has been under close scrutiny since 1988 by Kevin McGowan of the Cornell Laboratory of Ornithology and his students, who have marked as many as a thousand individual crows and keep track of each bird as an individual. Crows are extraordinarily intelligent and sociable, and family units remain together for a long time, with young birds typically helping their parents raise new broods for a few years before they find a mate and start their own families. But in 2002, fully a third of McGowan’s study birds were found dead from West Nile Virus, and last year another third died. McGowan likens the impact on crows to the effect the Black Death had on humans. Crows don’t abandon their family members as they die—McGowan says that at least one crow always remains with a dying bird. In one family unit of 8 birds, all but 2 have died from the disease, and the surviving females have joined other family units and help them raise their babies. Orphaned fledgling crows have been adopted by other crows. Widowed adults are moving back in with their parents. Crows apparently can’t live alone, and even pairs won’t nest without a whole group, which will slow the speed at which the survivors will repopulate the area. Many people don’t like crows, the most human-like of all birds with their complex language and social behaviors and intelligence. But our measure as human beings is related to how much compassion we have for all the creatures on this little planet. The Bible tells us that God specifically instructed Noah to save every species. American Crows are too numerous to be in any real danger of extinction, but whether you find them a worthy adversary, an intelligent neighbor, or an entertaining nuisance, the world is diminished by so many of their deaths, and attention must be paid.