Key takeaways
- In years when pine cone production is very low, forest songbirds sometimes migrate in large numbers into cities, where they congregate around bird feeders.
- In these crowded conditions, salmonellosis, the illness caused by the Salmonella bacterium, can spread through their population and even sicken people, pets and poultry.
- UCLA researchers are developing a tool that can predict when these outbreaks are likely to happen so people can take down their feeders to prevent the epidemic from starting.
UCLA biologists are developing a tool to predict when deadly salmonella outbreaks are likely to happen in wild songbird populations so that people can protect their feathered friends by taking down bird feeders at the right time. The research is published in Proceedings of the National Academy of Sciences.
Wild birds that depend on conifer seeds often descend en masse into cities during years when pine cone production is low, and flock around bird feeders. In these crowded conditions, disease can spread easily, and the best way to keep birds and people from getting sick is to take feeders down. For example, in the winter of 2020-2021, the Centers for Disease Control and Prevention traced a salmonella outbreak that sickened several people and a dog to a finch called a pine siskin, which was passing the bacteria around at backyard bird feeders.
But by the time an outbreak is detected, the disease is already racing through the population. Advance warning would give people time to take down feeders to prevent outbreaks from starting in the first place.
"While it's something that brings us pleasure and generally seems to have neutral or in some cases net positive ecological impacts, there are situations in which the gathering together of birds is bad for bird and human health," said senior author and UCLA professor of ecology and evolutionary biology Morgan Tingley. "We don't want people to stop feeding birds, so we're trying to develop a tool that will predict when there will be millions of extra birds flooding urban bird feeders so people can temporarily take them down."
Tingley and lead author Benjamin Tonelli, who conducted the research as a doctoral student at UCLA, developed a tool that finds linkages between climate patterns, tree cone production, irregular avian migrations and zoonotic outbreaks of salmonellosis, the disease caused by salmonella. Like oak trees, conifers mast, which means all the trees in a given region produce large amounts of cones all at once some years and other years produce very few or none at all. Masting is known to be connected to climate.
The researchers pulled data from the past 40 years from four different databases. A USGS database for disease outbreaks in wild animals provided estimates of how many songbirds were sick with salmonella, and how big those outbreaks were in every year. The Audubon Christmas Bird Count gave them numbers for winter species and population size. Information about pine cone production in different forests across North America came from an academic study of masting. NASA's Daymet project, which provides estimates of daily weather and climatology variables for North America, supplied climate data.
The research found a clear throughline through each of these ecological levels, and that measured relationships between each of these levels could forecast upcoming disease outbreaks that affect both people and birds. This ecological cascade was quite dramatic – when there are large differences in temperatures between years, forests can produce substantially fewer pine cones.
The results held for the two major regions studied: east and west of the Rockies. The patterns were stronger for the western region however. Sudden winter mass migrations, called irruptions, and salmonella outbreaks in the eastern region were likely to be somewhat milder and more localized, whereas in the West they were more intense and widespread.
Bird-related activities are one of the most popular ways that Americans experience the environment. One of the current estimates is that one-third of American adults engage in some sort of activity with birds, whether that's observing or feeding birds, and that about 40 to 50 million people purchase bird seed every year.
Birds transmit the Salmonella bacteria when a healthy bird pecks for seeds in the same place where a sick bird has pooped, inevitably swallowing some of the pathogen. Backyard chickens can be infected if they're pecking around near the feeder, as can dogs or other pets. Humans can also get sick if they handle dead birds. But the biggest threat is to wild songbird populations, which are already declining due to climate change and habitat loss.
"The good news is that the last major salmonella outbreak was in 2020-2021, so they're not happening every year," said Tonelli, who is now a postdoctoral researcher at Clemson University. "You can feed your birds basically 99% of the time without having to think about this. But there is going to be a time and a place where the best thing you can do to protect your backyard birds is to take down your feeders."
The researchers said that the model is still up and running, and so far, the prediction is looking pretty good for birds.
"So far this year, it predicts a pretty average season in both regions for irruptions, and therefore pretty average risk of disease outbreaks, which means not heightened really at all," Tonelli said.
The research was funded by NASA's Earth and Space Science and Technology division.
