Salmonella At Bird Feeders – Is It Really A Problem?

Plus recommendations for types of bird seed to purchase for the birds you intend to feed and tips on cleaning bird feeders.

This is the time of year that some “authorities” recommend that we stop feeding birds because of problems with Salmonella at our bird feeders. However, new research suggests that Salmonella at feeders may not be a significant problem, if it’s a problem at all.

 

Lesser Goldfinches at one of my feeders a few days ago

Followers of my blog know Dan Gleason as a highly knowledgeable, regular contributor to Feathered Photography. Recently Dan wrote an article addressing the issue of Salmonella at bird feeders that includes, among other relevant information, the results of new research on the subject. Both Dan and I believe that making that information available quickly to large numbers of folks who feed birds is important so with Dan’s permission I’ve included his article below in its entirety.

It’s a long read and parts of it may not be of great interest to some of my viewers because those parts are somewhat specific for Pine Siskins, a species that may not be present in your area. So I’ve taken the liberty of color coding certain paragraphs that should be of interest to anyone who feeds birds to make those portions near the end of the article easier to find for my readers.

Types of seeds preferred by different species of birds.

How to properly clean bird feeders to prevent disease.

Ron

 

Salmonella at Bird Feeders
© 2021, Dan Gleason, Ornithology Instructor, retired, University of Oregon
Co-Owner of Wild Birds Unlimited, Eugene, Oregon

Each year it seems that fears arise concerning Pine Siskins and the risk of their contracting Salmonella. This fear leads to wildlife managers and others advising citizens to stop feeding birds. We know that many kinds of wild birds carry Salmonella, and dead Pine Siskins are often found where large concentrations of birds are found. The assumption has always been that Salmonella is transmitted from bird to bird at feeders where they are found in significant numbers. There is new evidence that this may not be the case, or at least it may not be as significant as believed. The advice for removing feeders is not based on research, but on historical belief. This new research may lead to different advice, not to remove feeders, but to maintain or begin more thorough cleaning, to help protect birds against ALL disease.

Salmonellosis is the disease caused by the Salmonella bacteria which can infect the gastrointestinal tract of animals, including humans. Many wild bird species carry these bacteria, but most are not severely affected by it, and often show no symptoms at all. However, Pine Siskins and Redpolls are especially sensitive to these bacteria, for unknown reasons, and once infected and symptoms appear, these birds will invariably die within a matter of hours.

Bird seed supplied at bird feeders will NOT cause salmonellosis. The bacteria may be carried to feeders by birds from their wild activities but in what amounts is not known. It is not an airborne disease and is not spread through direct contact of individuals. It is carried in the droppings of infected birds and the bacteria may live on the ground for long periods of time. It is transmitted to a new individual when that individual eats food that has been contaminated by fecal droppings from an infected bird.

But it’s not as simple as that. It is known that infected birds may defecate but not shed the bacteria in the fecal droppings. It remains largely unknown for what time period bacteria are actively shed, and very little data exists to show how long the shed bacteria remain viable. A study with Herring Gulls found that infected individuals only shed the bacteria over a period of 4 days. No data exists for songbirds. Another study found the Salmonella bacteria remained active in the dropping of Canada Geese for up to 16 hours. But such a timeframe may realistically be much shorter in songbirds because their droppings are small and the bacteria is subject to desiccation much more quickly. Birds seen dying at feeders most likely had the disease before coming to the area where the feeders are located and did not acquire the disease at the feeder. Much more research needs to be done to understand the nature of Salmonella in wild birds and not simply make assumptions that appear valid but may not be.

Recently published studies have shown NO transmission of Salmonella at feeders. A study in Poland (published in June 2021 from data collected during the winter of 2018) examined 204 feeders and found no incidence of Salmonella being transmitted at feeders. A similar study in Canada also found no evidence of Salmonella transmission. 1

Before the study began, the researchers assumed that the birds transmitted Salmonella and the intent of the study was to determine how much transmission occurred and did such transmission also present a human risk. Each of these studies examined food covered with droppings and scrapings from the feeders, including scrapings from encrusted fecal material. In the study in Poland, the researchers deliberately did not keep feeders clean, to simulate the conditions at most feeders where people are not as fastidious as might be ideal. Each study looked for the presence of Salmonella and other diseases. Salmonellosis was a disease present in the wild populations of the birds at the study sites but no evidence could be found of Salmonella bacteria at the feeders or any transmission of this disease at the feeders. In other words, the disease was not being spread from bird to bird in their droppings.

Some other studies have found some transmission of disease but not in large volume as is often suggested and implied by wildlife officials’ warnings. A Scottish study found only a 2% rate of transmission. The researchers of these studies found that differing environmental conditions may play a large role in the spread of and action of Salmonella. While it can persist for long periods of time in the soil, some bacterial studies indicate that it becomes inactive and cannot cause disease at prolonged temperatures below 39°F. The studies done showing no transmission of Salmonella at feeders were done during winter feeding, when daily temperatures were cool. The studies in other areas showing some disease transmission included warmer spring conditions. It appears that many of the sick birds visiting these feeders acquired the disease from wild sources and did not acquire it at the feeders. Most instances of Salmonella occurrence in wild bird populations in the Northwest US are found during winter or early Spring conditions, similar to the conditions where the research was done. But much more investigation needs to be done. At this point it remains unknown how much, if any, disease transmission occurs in mild to warmer temperatures. It may still be very low and other factors need to be examined as well. It is not safe to make assumptions that simply seem logical but are unsupported by hard evidence.

Siskins sick with salmonellosis are typically very lethargic and usually find a branch or perch away from feeders once symptoms begin. Siskins die within hours of showing symptoms of the disease. So, they may be infected when they arrive, but very soon afterwards they are infrequently seen to visit the feeders and do not leave infected droppings where the majority of birds are feeding. The cooler temperatures may further help minimize the development of any disease. Plus, as stated above, it is unknown how long birds can actively shed active bacteria even if they are infected. Once symptoms begin the birds soon die. It is unclear if they actively shed bacteria during that period.

Watching and feeding birds is an enjoyable activity for humans and does benefit the birds, but it carries with it a certain level of responsibility on the part of those feeding birds. It is vital that you provide safe conditions for the birds you attract. It is inappropriate, for example, to attract birds to a site where cats can easily and frequently prey on them. It is also inappropriate to have unclean and unsanitary conditions that put visiting birds at risk.

Keeping feeders clean is not a difficult task but may require more diligence and effort on your part at certain times of year. If you see large groups of Pine Siskins coming to your feeders, increase your efforts to provide clean conditions to help prevent possible spread of disease. But if you take proper precautions (see below) there is no reason that you have to stop feeding.

It has been suggested in one article in a Washington state Audubon chapter (it is not known what background in science or biology the writer has or who they consulted with prior to making their claims) that no-mess seed—seeds with the shells removed—put the birds at risk because the birds don’t need to carry the seed away to open them, and they therefore stay at the feeder and contaminate the feeding area. This is simply not true for many birds. Chickadees and nuthatches carry away whole seeds to open them away from the feeder, but chickadees and nuthatches do not show symptoms of salmonellosis. Goldfinches and Pine Siskins generally remain at the feeder while opening and removing the shell of whole seeds, just as they do when feeding on shelled seed.

Any naked seeds, whole or broken, that fall to the ground are usually quickly eaten before there is time for them to become contaminated. Whole seeds that fall to the ground are equally likely to become contaminated, and the seed inside does not itself need to be contaminated. If any bacteria is on the seed shell, birds would acquire that bacteria while opening the shell, since they are opened with the mouth, allowing bacteria to enter the gut. But since the bacteria is inactive at low temperatures, there should be little infection. The bacteria may become warmed once inside the bird, but the bacteria are likely passed out in the feces before they have time to warm, reactivate and have time to grow sufficiently to cause infection.

The ground below a feeder needs to be kept clean no matter what type of feed you use. The shells of whole seeds, (and by the way, this includes Nyjer which has a shell the birds remove before eating it), will fall to the ground and begin to accumulate. If allowed to remain long on moist ground, mold can begin to grow. Specifically, Aspergillis, a common mold, often flourishes. The spores from this mold can infect and grow in birds’ respiratory systems and be fatal. Additionally, an accumulation of shells on the ground often attracts rats and mice in search of food, since shells still have food odor left in them. An easily cleaned plastic tray mounted below each feeder to catch what spills is often a better solution. Be sure the tray is also kept clean to prevent an accumulation of feces from the birds feeding above it.

In addition to whole sunflower seeds, the Audubon article suggests switching your food to millet, safflower or cracked corn. But these are NOT good solutions for most birds that people have at feeders. Millet is small and good for some ground-feeding birds such as sparrows and juncos. But larger birds or birds used to feeding in trees or at feeders hanging from hooks do not want, and rarely eat millet. For these birds, the energy expended to open such a small seed is not worth the reward inside. Smaller-beaked sparrows (like juncos, Golden-crowned, Song or other sparrow-sized birds) can more efficiently open these seeds. So, many birds simply toss aside and scatter the millet in search of larger seeds. If the ground-feeding birds are not around to take these scattered seeds, the seeds risk becoming moldy in the same way as do the shells of whole seeds. Many of us also do not want to attract non-native House Sparrows, but House Sparrows are grain-eating birds, so are very attracted to millet. Sunflower in any form, however, is not well liked by House Sparrows. So, to avoid attracting House Sparrows, many in the bird-feeding public avoid the use of millet.

Cracked corn is also rejected by most birds who simply toss it to the ground. Some doves, quail and ducks will eat it, but most bird species coming to feeders reject it. It is often in cheap blends of so-called “wild bird food” because it is relatively inexpensive and adds bulk to the bag of seed. You pay for it, but most birds don’t want it so the cost of any remaining food in your bag of seed is actually higher per bag of seed. (The same is true of other fillers in cheap bags of seed which can include unwanted wheat, rye and milo.) Unless you deliberately want to feed doves and quail, and have such birds in your habitat, you may want to avoid the use of corn.

Safflower seed is not the best choice for many of us in the Far West. Cardinals in the East love it, but for many of our western birds, it is a last choice. If nothing else is available they may eat it, but they would prefer something different first. The hard shell makes it difficult to open and the bitter taste is not well-liked. In an inexpensive mixed blend of seeds, the birds often toss safflower to the ground as they search for something more enticing. A thinner-shelled safflower is now available in some places and is easier for the birds to eat, but it is still not taken as readily as is sunflower.

One other perceived “problem” with no-mess blends of high-quality seed I would like to dispel, is the supposed high cost. Yes, a bag of sunflower out of the shell or a no-mess blend usually costs more per bag, but an equal-sized bag of whole sunflower contains more than 40% shells, so the amount of food — the remaining 60% — is less in the same sized bag. Pound for pound the amount of actual edible food is approximately the same price as the food with shells, so switching to whole seeds may not really save you money. Either option is fine as far as the birds are concerned but whichever you choose, be sure to keep debris below the feeder at a minimum, especially when large numbers of birds begin to congregate.

Feeding birds is an enjoyable and beneficial activity but do so responsibly. Keeping the birds safe is important. If you see sick birds at or near your feeder make efforts to keep all feeders clean. If you see groups of Pine Siskins beginning to congregate at your feeders, you may want to reduce the number of feeders if you have quite a few. With a reduced supply of food available, fewer birds may congregate and you will have less cleaning work to do. If you are diligent about keeping your feeding area clean and safe, you are not putting the birds at risk. Salmonella is a naturally occurring bacteria and is carried by many kinds of birds. It is common in the wild and does NOT come from your feeders. Chance of infection is minimal, but clean feeding areas can reduce that risk even more and allow you to continue enjoying the birds around you.

It should also be noted that there is some risk of human infection. To become infected from handling birds, you must somehow get contaminated fecal matter in your mouth. This can happen if you handle a bird that has died from salmonellosis and if you then don’t thoroughly wash your hands, or if you touch your mouth or handle food you then eat without washing your hands. Be diligent about hand-washing any time you handle birds or bird food.

If sick birds are seen and a person acquires a case of salmonellosis, the assumption may easily be made that it came from the birds. That’s actually rather unlikely. Salmonella is a very common bacteria and the most common cause of food poisoning in people. Tens of millions of cases are reported worldwide each year. It can come from many sources including some raw fruits and vegetables, eggs, raw or undercooked meat, especially poultry, or from egg products, such as mayonnaise, allowed to sit open for hours at warm temperatures, and many other sources. Some people infected show no symptoms, but many have mild to severe diarrhea. Some cases require hospitalization and death can occur but that is rare. Human cases of salmonellosis are unlikely to have come from birds.

Without reliably knowing the source of a Salmonella incident, it may simply be coincidence to have a human case at the same time as an outbreak in birds. But always be sure to use good sense and good hygiene just to prevent the possibility. The hazard of blaming birds, though, is that a local food source actually causing the outbreak could remain undiscovered because of blaming birds for a human case of salmonellosis.

It has been assumed that outbreaks of salmonellosis are more likely when birds congregate at feeders. But long-held assumptions sometimes prove to be false. More data is needed but some new studies are challenging those assumptions. It’s beginning to look like the rate of Salmonella transmission at feeders is very, very low or even 0 in many instances.

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How to Clean Feeders Properly to Prevent Disease
If droppings are encrusted on the feeders simply cleaning with bleach or other household disinfectants will NOT be sufficient. As the bacteria become established, they form what is known as a biofilm. A matrix of material is formed around the bacteria and this biofilm becomes completely resistant to bleach and other disinfectants. It is necessary to break up and remove this biofilm.

To remove the biofilm and correctly clean feeders, scrub the dirty areas with hot, soapy water and use a good scrub brush. The brush will break up the encrusted film and the hot, soapy water will help lift it from the surface. Once you have completely cleaned the surfaces you should then use a 10% bleach wash to disinfect the area, leaving the feeders in the bleach solution for perhaps 10 minutes. Following these actions, be sure to rinse the bleach away with plenty of water. Let the feeders air dry completely before refilling. If you keep your feeders well cleaned at regular intervals such intense cleaning should seldom be necessary.

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1 Lack of Evidence that Bird feeders Are a Source of Salmonellosis During Winter in Poland. Martyna Frątczak,1 Piotr Indykiewicz,2 Beata Dulisz,3 Jacek J. Nowakowski,3 Tomasz Janiszewski,4 Jan Szeptycki,5 Jaroslaw Wilczyński,6 and Piotr Tryjanowski1,*