[Tweeters] Feeders , Pine Siskins and Disease

Kim Thorburn kthorburn at msn.com
Fri Jan 22 15:32:34 PST 2021

Hello Keith and Birder Friends,

Here are some thoughts about "evidence."

Wildlife don't tend to cooperate with randomized controlled trials. Consequently, the most common "evidence" collected in research on wildlife is associations. While a factor, association alone does not prove cause and effect. Biologic considerations are also helpful. So...

Let's start with feeder associations: One of the best studied transmissable wildlife diseases associated with feeding is chronic wasting disease in elk. If there's CWD around, it tends to be concentrated around feeding operations where there is congregation of high numbers of animals. With game species like elk, we can get other data from harvested animals that add information about CWD transmission. The latter data are generally not available with songbirds that are, of course, not hunted. It's hard to postulate much about Keith's question about pine siskin infection transmission at sites other than feeder congregations.

Turning to biology: Salmonella is transmitted through the fecal-oral route, meaning the bacteria are shed in the feces and transmitted when the infected feces is swallowed. Feces does certainly soil feeders. Another biologic fact is that infectious agent susceptibility and even more, virulence can vary among species. Salmonella is common in domestic chickens but illness is not. It is the reason that we're counseled to not eat raw eggs.

There are some biologic and association data, but not necessarily proof, that we may want to consider regarding the risk that feeders are contributing to a salmonella disease outbreak in the state. It's up to each of us how we want to deal with the risk assessment.


Kim Marie Thorburn, MD, MPH
Spokane, Washington

From: Inland-nw-birders <inland-nw-birders-bounces at uidaho.edu> on behalf of Keith Carlson <kec201814 at cableone.net>
Sent: Friday, January 22, 2021 2:59 PM
To: inland birders <inland-NW-birders at uidaho.edu>; Tweeters <tweeters at u.washington.edu>
Subject: [inland-NW-birders] Feeders , Pine Siskins and Disease

This is all very confusing.
We are being told/encouraged to take down our bird feeders and bird baths to prevent the spread of salmonella in Pine Siskins.
Is this not an admission that Winter feeding is not necessary/useful and done for our pleasure, not for the birds ?.
If there is no feeding, will any die off stop or simply occur where not so visible ?

Is this more of a problem than the usual loss of birds due to the attraction of avian predators such as accipiters and house cats ?

What evidence do we have of disease spread in other species using the feeders ?

Does this disease occur in Pine Siskins in years where there is not a visible irruption and to what effect on populations ?

Recently, I commented on seeing many flocks of siskins and some of Common Redpolls on US Hwy 12 where I'm sure significant numbers were killed by traffic.

I certainly enjoy seeing the many species at our feeders and am willing to take them down if it is established that it is harmful, but so far the evidence seems weak.

Keith Carlson
Lewiston, Idaho
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