I just got a call from Carrol Henderson. The early tests on the redpoll carcasses had suggested that the redpolls and siskins were dying of something viral not fungal, however the tests have concluded that the redpolls died of Salmonella E.
This outbreak of salmonella is widespread with reports of dead birds from several areas including Minnesota, Vermont, Virginia, Michigan and Quebec just to name a few.
One of the ways birds are probably spreading it is through fecal material built up around feeding areas. The best thing to do when this occurs is remove finch feeders and thoroughly clean them. It is also a good idea to keep the feeders in for a week to encourage the redpolls and siskins to move on to other areas and cut back on the chance of it spreading at your feeder. Also, it is important to clean up the area under the feeders as well.
One one other note is that salmonella is transmittable to cats so if you have a problem with a neighbor's cat at your feeder, you might want to warn them to keep their cat indoors for a week (or preferably the rest of the cat's life).
For more information go here.