This is very interesting. Although I know nothing about all this,
wouldn't such a high die-off rate engender rapid evolution of resistant
siskins? And relegate the disease to a background status? Or are the
strains different every year?

Bob Mauritsen


> Tom Besser wrote:
>
> Tweeters:
>
> I'm a diagnostic microbiologist and I find Siskin salmonellosis a very
> interesting problem though I certainly don't have any solutions. There
> is a literature on the subject, and it confirms that Pine Siskins are
> the most susceptible finch species in the US. Siskin salmonella
> die-offs have been recognized around the country as an almost annual
> event.
>
> Last year, I solicited samples from dead Siskins from Tweeters and
> others who have seen feeder death birds (and of course I've seen the
> problem at my own feeders as well). In 1999, the salmonella isolates
> from Siskins (and a few Grosbeaks, Goldfinches and House Finches) from
> Montana to Puget Sound, and from the Canadian border to southern
> Oregon were all a single identical 'fingerprint' strain of <Salmonella
> typhimurium>, and that strain as not found at all among several
> hundred human and animal <S. typhimurium> isolates from that year.
> This suggested that Siskins were carrying a unique salmonella around
> with them. (I also tested birdseed samples from many Tweeters, to see
> whether the salmonella could have originated and been spread around
> with thistle or sunflower seeds, but all have tested negative,
> suggesting that this is not the source of the problem.)
>
> If Siskin salmonellosis follows the same patterns as salmonellosis in
> other animals, it's very likely that any concentration of the birds
> will contain one or more carrying this strain in its intestines,
> probably with no apparent illness. Any persistent concentrations of
> birds (read, feeder stations) are likely places where the
> comtamination will become heavy enough to cause sickness, and sick
> birds will shed much higher levels of the bacterium, leading to more
> sick birds.
>
> If that is the case, Dennis is absolutely right that disinfecting
> feeders will have no practical beneficial effect. The contamination is
> not just on the feeder, it's probably in the birds themselves and it's
> certainly in the ground around the feeders where the birds also spend
> a lot of time foraging. No disinfection (other than drying and
> sunshine and time, hard to find in the PNW springtime) can effectively
> disinfect the ground.
>
> The best solution seems to me to be to disperse the birds, by stopping
> feeding for a while. It's hard to say whether this will actually have
> much of a positive effect: it could be that flocks in urban and
> suburban areas will just head to the neighbor's feeder where the same
> problem will persist. (In fact, it's possible that the same problem
> could be occurring in Siskin flocks that never visit feeders: a lot of
> Siskins could die in the woods without being noticed.) Still, I think
> stopping feeding when you find dead Siskins is sensible, and more
> likely to have a beneficial effect than disinfecting feeders.
>
> Last, despite the fact that the Siskin salmonella strain hasn't
> appeared in human cases in Washington, it undoubtedly has the
> potential to infect you and make you (or more likely, your children)
> very unpleasantly sick: Don't forget to wash your hands very carefully
> with hot soapy water after touching your feeder or a dead bird.
>
> Tom Besser
> Moscow ID
> tbesser at vetmed.wsu.edu
>
> by way of Edinburgh Scotland
> (where 'feeder table' salmonellosis is also a problem)