Animal Outbreak: Salmonellosis in Songbirds
I was on a run the other day when I found a small, fluffy bird on the ground. It was struggling to move about, and at first I thought it might be a nestling that fell too soon. Nevermind that it is January and I don’t know of any birds besides eagles that lay eggs in the winter, I just wanted to help. As a child I rescued a few baby birds, so I noticed that this bird was behaving oddly. It was unusually comfortable with my being near and had difficulty breathing. It attempted to fly but could only make it a few feet before its wings gave out. I called the West Sound Wildlife Shelter to get an expert opinion on what I ought to do. While on the call, the bird tried to take off, at which time a crow swooped down and made a meal of the tragic fellow. “Well, that’s the end of that…” Jason, the phone operator, mused. He then explained what I was seeing with this little bird.
Animals deal with outbreaks and epidemics, just like humans. While this is not surprising, it is something you might not think about if you don’t work with animals. Currently, on the west coast, there is an outbreak of Salmonella in the wild bird population. The bird I met is called a Pine Siskin, and this species is particularly susceptible to Salmonellosis, the disease caused by infection of the microbe, due to their small size and social nature. In fact, they are often the canary in the coal mine for Salmonella outbreaks in local bird populations because Salmonellosis is so deadly to them.
I was told that a number of sick birds have been brought in recently, most of which do not survive the infection. As you may know, my research interests are focused on infectious disease, so I have been reading all about this outbreak since my odd encounter. Here is what I’ve learned.
What is Salmonella?
Salmonella is a genus of rod-shaped, gram-negative bacteria; you’ve probably heard of someone getting food poisoning from Salmonella. Typhoid Fever is another type of infection caused by a species of Salmonella, S. typhi. They are intracellular pathogens, meaning they can invade cells and reproduce inside them. You can be infected with Salmonella from food, wild animals, and also pets. Some animals (Such as chickens, turtles, and iguanas) are reservoirs for Salmonella, meaning they are a natural host for a microorganism and do not typically get sick from carrying it. If another host (human, or otherwise) is not a reservoir for a specific microbe and they are infected, they can become sick. This is what is happening in the bird population at present.
How is it spread among birds?
These bacteria are typically spread by the ingestion of food or water contaminated with fecal matter of an infected individual. Pine Siskins are social creatures, and can spread the bacteria by interacting with one another. Birds gather at bird feeders quite heavily in the winter months, where their droppings and saliva can easily contaminate the food supply.
Why is this such a big problem this year?
This winter has seen a large irruption from Canada, or a mass migration of birds due to fewer resources in their typical winter habitat. Canada’s Boreal forest had an usually low crop of conifer seeds this year, resulting in birds flying further south in search of food. This year’s irruption of Pine Siskins is one of the largest ever recorded, according to the National Audubon Society. Infected birds carry the bacteria with them as they fly south and infect other bird populations. An outbreak of Salmonella combined with an exceptional mass migration of Pine Siskin is a recipe for rapid spread of this bacteria.
Salmonella is treatable in humans, but what about birds?
Although Salmonellosis is treatable with medication, many wildlife rescues do not treat infected wild birds using antibiotics and allow nature to take its course. At first it may sound cruel, but there are thoughtful reasons behind this decision. According to the Canadian Wildlife Health Cooperative:
No treatment is recommended for infected wild birds because it requires the use of antibiotics, which could cause some birds to become asymptomatic carriers of the disease and/or antimicrobial resistant Salmonella bacteria, and either of which increases the possibility of salmonellosis spreading in the bird population.
What are the signs of infection in birds?
Signs of infection may include:
Unusual friendliness/ tame appearance (wild birds typically aren’t like this)
Puffed out feathers
Partially closed eyes
Above is a healthy Pine Siskin on the right, captured by Douglas Faulder for the Macaulay Library On the left is a closeup of the bird I saw, with its feathers puffed out and its eyes partially closed.
What to do if you find a sick bird?
Contact your local wildlife rescue to find out what their protocol is. Some places may recommend bringing the bird in, while others recommend leaving it be. The Washington Department of Fish and Wildlife (WDFW) is asking folks leave the birds alone and report the sighting of dead birds online. If you do touch the bird or anything the bird has been on, make sure to thoroughly wash your hands! Salmonella is zoonotic, so it can be transmitted from animals to humans and vice versa.
How can we prevent the spread of this bacteria?
Rescues and the Audubon Society recommend removing bird feeders, especially if you see a sick or dead bird near your feeder. Birds can and will forage themselves, and the removal of the feeders encourages social distancing! If you’re an avid bird watcher and you don’t want to get rid of your feeder, you should be cleaning bird feeders daily and diligently. The Seattle Audubon Society suggests using warm, soapy water, followed by disinfection with a solution of 10% bleach to kill the bacteria on all bird feeders and birdbaths. More instructions can be found here.
Hopefully the Salmonella outbreak can be under control by spring. Special thanks to Jason at the West Sound Wildlife Shelter for being so helpful and informative!