This is a Guest Post by Dan Gleason, Instructor of Ornithology, University of Oregon and Co-owner of Wild Birds Unlimited - Eugene, OR (opening April 2013)
During winter finch irruption years like we're experiencing right now, we unfortunately start to see birds that are obviously sick or find a dead bird near our feeders. The cause if often Salmonella bacteria. Here's a good discussion on a sometimes confusing subject by Dan Gleason, who has taught ornithology at the college level for over 30 years.
The Many Types of Salmonella BacteriaThe usual cause of sick and dying Pine Siskins is Salmonella bacteria. There are two primary species of the Salmonella bacteria that often infect birds, but these are subdivided into over 2,300 variants. To make matters more confusing, some of these variants are sometimes referred to as if they were a separate species; e.g., Salmonella enterica typhimurium (a common type of fowl typhoid) is often simply called S. typhimurium. This can make it confusing when trying to find information online about Salmonella.
One of the two species of Salmonella (S. pulorum) most often infects waterfowl and grouse, and most frequently, domestic fowl. The other species (S. enterica and its many strains) is what infects many wild birds (and people).
Birds React Differently to the Bacteria
Different species of birds can react differently to infections of Salmonella. One study on Herring Gulls showed they passed out the bacteria in their feces and showed no physical symptoms at all. Some kinds of birds show mild lethargy for a day or so, but little else.
On the other end of the spectrum are Pine Siskins, which seem to be more susceptible than any other species. I don't know the physiological reasons for such differences (or if they are even known), but it seems to be the case that Pine Siskins have a much higher mortality rate from this disease.
A friend of mine who has an international reputation among wildlife rehabilitators and has over 30 years of experience, tells me that she has never successfully been able to save a Pine Siskin that has been infected with Salmonella. They always die before any treatment has time to work.
Salmonella is less frequent, but still very common in Evening Grosbeak, House Sparrow, Brown-headed Cowbird, Northern Cardinal, and Goldfinches (especially American). It occasionally occurs in House, Purple, and Cassin's Finch and is infrequent to rare in most other species of songbirds.
How the Bacteria SpreadsSalmonella as a disease in birds is relatively rare in the wild, but outbreaks do occur from time to time and then we often see the evidence at our feeders. Many birds with mild infections can carry the disease without showing any symptoms and simply pass it out in their feces. But the bacteria is still active.
When a susceptible individual of an easily-infected species, like the Pine Siskin, picks up the bacteria, it proliferates quickly in the infected bird's gut and is passed along to others via the feces.
Salmonella is most easily passed between individuals by contact with the feces from infected birds. Pine Siskins are especially social, allowing easy transmission of the disease. Feeding in close association with one another makes it a certainty that the disease will be passed to other individuals from an infected one.
What You Should Do with my Birdfeeders?It is recommended that feeders be cleaned with a 10% bleach solution (9 parts water to 1 part bleach) followed by careful rinsing and complete drying before reuse.
Clean the area beneath the feeders as well, bagging the debris to be disposed of in the trash. Pine Siskins can be messy eaters and spill many seeds on the ground. It is inevitable that some of that spilled seed will be contaminated by feces.
It is also recommended that feeding be stopped for a period of time (2 weeks?) to let the birds move on and not get reinfected.
Keeping feeders clean is essential, but unfortunately, that alone will not prevent the spread of this disease. The bacteria can survive for many months on uncleaned feeders, on the ground, on plant or other surfaces. It can be passed by other birds less susceptible to the disease, by reptiles, mammals, or even some invertebrates. Total prevention is almost impossible.
Once brought to a communal feeding area (which can be a feeding area in the wild or a birdfeeding station), the disease quickly spreads. Even if you are very efficient about keeping your feeders and feeding area clean, Salmonella may be brought in from surrounding wild areas.
Because Pine Siskins are the most susceptible, and because they are so tame and can be numerous at feeders, we see it in them most often. However, be assured that there is nothing wrong with feeding the siskins and that this disease is just as frequent in wild areas as it is at feeders. We just see it more easily at feeders because of their high visibility.
Am I Safe from the Bacteria?
This form of Salmonella can be transmitted to humans and is the most common type of "food
poisoning." It will cause extreme diarrhea and very, very intense intestinal pain. Death has been known, but is uncommon; however dehydration is typical and may be what ultimately kills the Pine Siskins.
Having experienced Salmonella poisoning personally (from an unknown source), I can assure you that you do not want this. It is the single most painful experience that I have ever had.
If you handle a sick or dead bird, or after handling birdfeeders where lethargic siskins have been attending, be sure to wash your hands very thoroughly (a good practice ANY time you touch a birdfeeder - sick birds or not).
Keep your feeders clean and intensify doing so when many siskins are frequent, but be assured that your birdfeeders are not the cause of this naturally occurring and cyclic problem.
Thank you to Dan Gleason for sharing the information for this guest post. Congratulations and good luck with your new Wild Birds Unlimited shop!
Post written by:
Dan Gleason, co-owner Wild Birds Unlimited of Eugene, OR (opening April 2013) and Instructor in Ornithology, University of Oregon.
Author: "Birds! From the Inside Out" and "Looking for Yellowheads".
Dan can be contacted at firstname.lastname@example.org.