Seabird “food theft” could be source of deadly avian flu

The deadly H5N1 avian influenza virus, which has killed millions of birds around the world since 2021 and can rarely infect humans, could spread through the food-stealing behaviour of some seabirds.

A study published in the journal Conservation Letters suggests that food theft, also known as “kleptoparasitism,” in which some seabirds such as frigatebirds and skuas regurgitate prey for other birds could be a way for avian influenza to spread.

Led by scientists from the Centre for Ecosystem Sciences at the University of New South Wales, Sydney, and with participation from BirdLife International, Deakin University and Monash University, the researchers analysed existing information on the distribution, behaviour and movements of frigatebirds and skuas, searched global databases for records of viral infections, and reviewed available literature to determine which seabird species frigatebirds and skuas target for kleptoparasitism.

Lead author Simon Gorta, from the University of New South Wales School of Science, said the study could provide a new focus in determining where and how the spread of the deadly virus occurs and how it is transmitted at individual, population, continental or ocean basin scales.

“Understanding the pathway of transmission is crucial for surveillance and control activities, particularly where at-risk species and regions are involved, and also helps us understand the threat to other animals and people,” says Gorta, a PhD student at the University of New South Wales.

“The original H5N1 virus first emerged in 1996, but the current 2.3.4.4b strain is much more widespread than other strains and is highly virulent, killing hundreds of thousands of wild seabirds since it was first detected in 2021.”

Previously largely confined to Eurasia and Africa, the virus spread to North America in 2021 and South America in late 2022. In early 2024, it reached Antarctica and was declared a pandemic among animals.

Seabirds are at risk and can transmit diseases

Seabirds and other marine life are particularly hard hit by this panzootic phenomenon.

“The fact that seabirds, one of the most threatened bird groups on the planet, have been found to be particularly vulnerable to this disease is of great concern,” said co-author Associate Professor Rohan Clarke, from Monash University.

Co-author Professor Richard Kingsford said seabirds were particularly vulnerable because of their gregarious breeding nature.

“Seabird-to-seabird transmission is of real concern because of close contact on densely populated breeding islands and the potential for contamination of communal resources, as well as the specific behaviours of infected individuals, such as predation and defecation,” he says.

But the researchers say another behavior may be playing a key role here: food theft, or “brood parasitism,” a behavior seen widely among seabirds, and which the researchers focused on in their study, a behavior commonly practiced by frigatebirds and skuas.

In this process, bandit parasitoids steal food by getting other birds to regurgitate their prey. If the bird targeted by the bandit parasitoid is infected, the regurgitated food will be coated with virus-laden saliva, potentially infecting the bandit parasitoid and potentially infecting other birds.

The researchers stressed that this route of infection could lead to the spread of the disease to new populations, but that it could also be transported long distances if migratory birds become infectious.

“Many seabirds, including these kleptoparasites, travel tens of thousands of kilometres during their migration,” said Alex Berryman, Red List Officer at BirdLife International.

“If the bandit parasite is transmitted during these movements and then comes into contact with other individuals in a way that facilitates transmission, the disease could spread to new, threatened, and previously uninfected populations and areas.”

Early detection is key

H5N1 2.3.4.4b has not yet reached Australia, but surveillance is underway to detect the disease early, not if it will reach Australia, but when it does.

“Birds around the world are already under unprecedented threat, so it is vital that the risks posed by avian influenza are properly studied and managed,” Gorta said.

“We have identified that migratory kleptoparasites, alongside predatory and detritivorous species, are likely to be some of the first species to be infected when H5N1 reaches Australia.”

These findings will contribute to the coordinated management of avian influenza in Australia, including through the National Avian Influenza Wild Bird Surveillance Program.

The researchers say this is important in guiding Australia’s preparedness for the arrival of the disease on Australian coasts, including vulnerable sub-Antarctic islands.