August 28, 2002

West Nile Virus

To our Sponsors and members:

Current hysteria in various media formats about the prevalence of West Nile virus, in birds across eastern North America, has suggested that we should issue a status report to members of the Owl Foundation.

The virus is indeed here, as well as being everywhere else, and we have lost a number of the total number of owls in all the 16 Canadian species we regularly house. In some species, the deaths seem disproportionately high; in others, inexplicably, there are no deaths at all. Theories abound as to why losses are so unevenly distributed among species. Amid the speculations, some facts stand out.

For instance, even with 35 Screech Owls (mostly vulnerable juveniles in training for release), we have lost none. The same applies to 2 Barn Owls and 10 Burrowing Owls. Of 10 resident Great Horned Owls, only one has died. The four resident Barred Owls are still with us, only one of four juveniles has succumbed. Eight resident Short-eared Owls in one complex are intact; all our resident Long-eared Owls are still here. Likewise all the Flammulated and Pygmy Owls.

On the other hand, in our four Northern species - Snowies, Great Grays, Hawk Owls and Boreal Owls, the death toll has been appalling. In trying to explain the differences, we have to recognize precipitating factores in the Northern species. One thing they all have in common is extremely dense plumage. This makes them less attractive to mosquitoes (the vector for West Nile Virus) but it renders them irresistible to a hippoboscid fly, another parasite of wild birds. Our sponsors may remember our ranting over the annual depredations of this cursed fly in newsletter after newsletter. The fly requires a blood meal to reproduce itself and it gets it in a curious way - by drilling a little hole in the lower shaft of a developing feather, still encased in nourishing blood. Enough of these "Flat Flies" on a single owl can reduce its packed-cell volume (haemoglobin) to dangeous levels. Action is required to remove the flies before he dies of anaemia.

Last year we had very few problems with these flies; this year is a different story. Our winter was so mild it did not kill the pupae from the flies which lie on the gound, then we had 6 weeks of rain in March and April which prevented us from removing the pupae and covering the ground with this cedar, then the weather was so hot in June and July that the Northern species simply suspended normal functions including eating.

Our need to handle the heavily feathered species for flat fly removal was the final stress they could not handle. These three things; blood loss, extreme heat and constant handling were inevitably the precipitating factors that eroded immune function in these very shy and vulnerable owls and opened the door of opportunity for a new virus. Unfortunately, a compromised immune defense is not as easily demonstrated in histopathology as the footprint of disease.

We clearly face three imperatives if we plan to continue housing Norther owls. Firstly, we need a vaccine against the new virus. We have already had 74 owls vaccinated, but the vaccine is new, its efficacy in owls is unknown and its applicaiton was probably several weeks too late.

Secondly, we have to find a solution to the flat fly problem. This is the tough one. We need innovative help from agricultural and veterinary communities - not only for the sake of future owls but also to look at the fly as a new potential (if only mechanical) vector for viruses like West Nile. After all, the mosquitoes that access blood from skin and the flat flies that only drink from feathers, both can transport blood. We need chemicals that neutralise the pupae on the ground under our cages to prevent emergence of the next generation of flies.

Thirdly, we must build an isolation ward of 16 to 20 units to control access of either mosquitoes or flies between birds that are arriving at the Foundation or those that are under suspicion. We needed it this past dreadful summer and work will commence on it this fall.

It is important to us that our members understand the present situation and recognize that all attempts to salvage damaged wild lives and make them productive again, can be viewed as a mine-field with no map. Some people think it is useless to try; others, like the staff of the Owl Foundation, feel that humans made the mess and it is bloody well up to us to do something about it. We hope you will agree and that you will continue to support us as we stumble on, looking for solutions.

Yours most sincerely,
Katherine McKeever
President, The Owl Foundation

Photo above: Adult Hippoboscid fly



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