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)