Birders,



Salmonellosis outbreaks seem to occur every few years in the Pacific
Northwest. Although they can affect many species of birds, these outbreaks
seem especially deadly to Pine Siskins and American Goldfinches. A brief
account of a major outbreak in 1992/93, which was published in the journal
BRITISH COLUMBIA BIRDS, can be read here:
http://www.bcfo.ca/publications/bcbirds-articles/vol_03/Bowes-1993.pdf .



No one is pointing a finger at bird feeder operators, but there is no
question that bird feeders do play a role in disease transmission. Pine
Siskins are highly social birds, usually travelling in large flocks, and it
is quite possible that salmonellosis could cause mortality even in areas
with few or no bird feeders. Sick birds are usually reported by people
operating feeders, hence the apparent concentration of affected birds around
feeders.



My suggestion to people concerned about the sick birds would be either to
stop feeding the birds for awhile, or to disinfect the feeders frequently
(at least once a week) with a 10% bleach solution. Siskins DO NOT need
feeders; in most areas, there is an abundant supply of natural foods that
they like (alder and birch seeds, western redcedar seeds, weed seeds, etc.).
Removing or disinfecting feeders may not stop an outbreak, even if EVERYONE
in an area does it, but it may slow down disease transmission.



It is distressing to see birds that are getting sick and dying near your
feeder, but it may continue no matter what steps you take to lessen the
problem. In most cases where birds suffer mass mortality like this, it is
because they have not been exposed to the disease very long (perhaps just a
few decades or less, in the case of siskins and salmonellosis), and have not
had time to develop a resistance to the disease organism through natural
selection. (A good example is the effects of West Nile Virus on crows,
grouse, and some other birds.) Chances are that, within a few more decades
(or less), siskins may develop a resistance to salmonellosis, like the
Australian rabbits did to the myxomatosis virus. However, in the meantime,
there may be relatively little we can do to stop the progress of these
outbreaks.



Wayne C. Weber

Delta, BC

contopus at telus.net