Wild birds come into contact with backyard chicken flocks more frequently than people realise, creating a pathway for pathogens to transmit back and forth, according to new research from the University of Georgia in the US.
Such pathways increase the risk for spill-over events that can threaten the health of all these groups – wild birds, backyard chickens and the people who care for them.
Warnell School of Forestry and Natural Resources and the College of Veterinary Medicine Professor of wildlife disease Sonia Hernandez said, “Most people probably don’t realise how frequently wild birds come in and take advantage of the food and water that’s put out for chickens.”
“Wild birds learn that resource and those contact points can become places where pathogens such as Newcastle disease virus and avian influenza virus can be transmitted back and forth.”
For the study, published in Epidemiology and Infection, Prof Hernandez and a team – including first author and postdoctoral researcher at Yale University who earned a PhD in comparative biomedical sciences at UGA Andrea Ayala – conducted a supplemental feeding experiment followed by observations at three sites with backyard chickens in north Georgia.
At each site, they identified the species of wild birds that shared habitat with the chickens, that were detected more frequently and that entered the coops.
The team identified 14 wild bird species that entered the coop to consume supplemental feed and were considered high risk for pathogen transmission.
“Interestingly, seasonality played a role – but not the one that we expected,” Ms Ayala said.
“We had hypothesised that feeding rates would be highest in winter, but for some species such as blue jays, the opposite was detected.”
Over 60 hours of observation, 1574 individual wild birds were detected across the three sites, comprising 72 species from 24 families.
There were some surprises in terms of species, according to Prof Hernandez. The sites attracted species that were seed eaters and grain eaters, and also some insectivores.
The presence of food presents an ecological opportunity that may attract birds who wouldn’t necessarily come down to the ground, Prof Hernandez said.
In the forest, some birds are at the very top of the canopy, some are in the middle, some are in the under story and some are on the ground.
“Offering supplemental food blurs those lines, because birds are more willing to cross those lines for a resource that’s provided artificially,” she said.
The best way to prevent contact between backyard chickens and wild birds is to offer food in a place that’s secure – in the coop behind mesh where chickens can access it, but wild birds can’t.
“Offering food in the coop saves the owner money, keeps the food from being exposed to rain and other elements, and minimises the amount of waste in the area,” Prof Hernandez said.
“If chickens are allowed to free range, don’t offer them food during that time.
“A songbird has no reason to come down near a chicken unless there’s a food source,” she said.
Wild birds can take advantage of the food and water that’s put out for chickens. Photos: UGA
Potential dangers of pathogen crossover
Songbirds and other wildlife are extremely vulnerable to the introduction of pathogens from domestic animals, Prof Hernandez said.
Newcastle disease virus and avian influenza virus circulate in backyard chickens, but there are other pathogens that can also circulate.
“Salmonella is something that kills songbirds every year, and mycoplasma makes songbirds sick,” she said.
Wild birds in North America are currently experiencing an avian influenza outbreak that’s severely impacting species such as bald eagles, vultures and waterfowl.
“Some of those species have needed very careful management to return them to viable populations because they were at the brink of extinction not that long ago,” Prof Hernandez said.
“Yet avian influenza threatens to undo all that effort, planning and careful monitoring.
“By studying how pathogens move among domestic and wild birds, we can better understand how to manage and prevent problems in the future.”
The study’s results confirmed that pathogen transmission is bidirectional, Ms Ayala said.
Wild birds can spread disease to backyard chickens, and backyard chickens can spread disease to wild birds.
Add in the humans that care for the chickens, and there’s opportunity for disease to spread into – or out of – that group as well.
“Families with children would be susceptible if they’re handling chickens that are shedding salmonella, since children are less likely to have good hygiene,” she said.
Last year, the Centers for Disease Control and Prevention reported an outbreak of salmonella typhimurium, which causes disease in people but also kills songbirds.
“What was unusual about that outbreak is that a high percentage of people reported contact with either wild birds or bird feeders,” Prof Hernandez said, who was working with the CDC on this topic.
“This paper is yet another piece of that puzzle,” she said.
“Sometimes people get sick and don’t know where it comes from.
“It’s possible that it comes from handling the dishes, the feeders or the waterers, either from the chickens or from the wild birds.”
Though pathogen crossover can have serious consequences, Prof Hernandez wants to promote awareness – and responsible practices – rather than fear.
“We live in an era in which the boundaries between human health and wild animal health are very tenuous because we’ve created circumstances that allow for crossover,” she said.
“We want people to be aware that all the things that impact the environment and impact the health of animals – pollution, contaminants and pathogens – also affect our health.
“We are not separated from our environments.”
For people who like to feed birds, Prof Hernandez suggested that instead of providing food, it would better to create a backyard habitat that allows wild birds to feed themselves.
“Given an opportunity to forage for natural food, songbirds will do better with that,” she said.
Allyson Mann
University of Georgia