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Pine Siskins and Salmonella
by Dan Gleason
Questions concerning sick Pine Siskins come up every few years, and this year seems to be a year when many of them are in our area and yet many are also falling ill.
As mentioned above, Pine Siskins will experience "irruption" years when many more birds than typical arrive in our area. In some of these years, some may become ill and perish due to salmonella. This does appear to be such a year, and some ideas on how to address sick siskins is below.
The 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 and to make matters more confusing, some of these variants are sometimes referred to as if they were a separate species. Thus, Salmonella enterica typhimurium (a common type of fowl typhoid) is often simply called S. typhimurium. This can be confusing when trying to find information online about Salmonella.
One of the two species, 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). 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, but presented 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 who 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.
Louise Shimmel, our friend and colleague, who has an international reputation among wildlife rehabilitators and over 30 years of experience, explains that she has never been able to save a Pine Siskin that has been infected with Salmonella. They always die before any treatment has time to work. It is distressing to see them come to feeders seeming to be so sick and dying. Some years we also find sick siskins at our feeders as well. These kinds of outbreaks of Salmonella are more common in the West than in the East, but I don't know why, as conditions are not that different.
Salmonella 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 Pine Siskin, picks up the bacteria, it proliferates quickly in the infected bird's gut and can be passed along to others via the feces.
Salmonella is most easily passed between individuals by contact with the feces from infected birds and Pine Siskins are especially social, allowing this easy transmission of this 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.
Keeping feeders clean is essential at such times, but unfortunately, that alone will not prevent the spread of this disease. It is recommended that feeders be cleaned with a 10% bleach solution (followed by careful rinsing then complete drying before reuse) and/or that feeding be stopped for a period of time of up to 2 weeks, to let the birds disperse through the habitat and not become reinfected. However, the bacteria can survive for many months on uncleaned feeders, on the ground, on plants or on other surfaces. It can be transmitted by other birds that are less susceptible to the disease, by reptiles, mammals or even some invertebrates. Preventing it is almost impossible. Once brought to a communal feeding area (whether to a wild feeding area or a feeding 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.
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.
Because 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 what you are doing 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 the birds’ higher visibility, but when outbreaks occur, they are just as frequent (sometimes more so) in the wild as at your feeders. In fact, the infections you see at your feeders were most likely brought in from wild areas, as Pine Siskins wander far and wide.
There is also no difference between using shelled or unshelled seed! The seed you supply is NOT the source of this infection. The bacteria is spread via the feces of infected birds which can get on either type of seed with equal ease. Pine Siskins can be messy eaters and spill many seeds on the ground. I have used both shelled and unshelled black oil sunflower and the mess below the feeder when Pine Siskins arrive is about the same. With many birds feeding at the same time, it is inevitable that some seed will become contaminated by feces. Because these birds are so social, this happens in wild areas just as frequently as at your feeders.
If you handle a sick or dead bird, or touch feeders where lethargic siskins have been attending, be sure to wash your hands very thoroughly! 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. (Dan says: “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.”)
Keep your feeders clean and intensify your cleaning routine when large numbers of siskins are present, but be assured that you are doing nothing to cause this naturally occurring and cyclic problem.