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Wednesday, December 07, 2022

Avian flu mutation in Scotland threatens thousands of sea birds

“What we’ve seen with this particular strain of virus is that it seems very easy to transmit,” says Ruth Cromy, consultant for wildlife health at the Convention on the Conservation of Migratory Species of Wild Animals.

It is not yet clear how this new form of the virus is transmitted from winter to spring, but it puts seabird populations at particularly high risk because they congregate in dense breeding colonies.

Scotland is home to about half the world’s breeding population, the largest seabird in the North Atlantic and a close relative of tropical boobies. shetland They have traditionally been a stronghold for them, because of their close proximity to the edge of the European continental shelf, the surrounding seas, which rise, are highly productive and full of food.

In mid-July, visitors traveling by boat from Lerwick’s capital Shetland to nearby Nose Island see thousands of gannets nesting on the narrow banks of the 182-metre sheer sandstone cliffs. The air is filled with birds that rise, as arrows are fired from all directions and which make their way amidst the hoarse sound of birds. crack crack, From time to time, the wind emits gusts of fish guano, which come from solid spots that hang from the sides like stalactites.

However, a closer look at the gannets through binoculars reveals corpses lying between the nests. At the base of the rocks, streams of water have pulled up white lumps formed by recently fallen corpses. A short distance away, a large skua – a species of bird – feasts on one of the floating gannets.

During this spring and summer, at times it was even harder to ignore the devastation. Phil Harris, a tour guide who takes visitors to Nose Seabird Colonies, describes how his boat navigates a floating body of 50 or 60 gannets.

“On three occasions we had dead adult birds coming from somewhere on the reef and dead with the boat,” he says.

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food chain transition

In addition, other worrying changes are taking place in the behavior of birds. Scotland is home to about 70 percent of the world’s breeding population of large skua, notoriously invasive birds that dare to reach their nests and harass other birds for free food.

At Nose, Harris regularly sees herds of great skua chasing gannets, forcing them to resume their catch. “You don’t see it anymore, probably because there are so many dead gannets to eat,” he says.

In some cases, within hours, birds begin to show neurological signs of infection, as the virus replicates in their brains and causes multi-organ failure. Gannets have been seen sitting helpless on beaches in Shetland, unable to see clearly. After large skua scavenge their carcasses, their infestation is evident, as are some swirling themselves in the air.

“It’s heartbreaking to see when they’re usually so full of attitude,” says Kevin Kelly. “These are huge birds that can’t keep their heads up. It affects them neurologically to a great extent.”

At the population level, the situation is even more worrying. Skua numbers on Shetland have dropped by at least half compared to last year. In some places only one in ten birds survives.

James Pierce-Higgins has received similar reports of mass skua mortality on other Scottish islands. If the current trajectory continues, the species could be a year or two away from extinction.

So far, reports of gannets have not been so severe, but in some colonies a quarter of adults have already died this breeding season.

Elsewhere, entire colonies of youth are being wiped out, including Tern on the island of Texel in the Netherlands. Hundreds of rosette terns have died on Coquette Island, the UK’s most unique seabird colony.

“You can quickly see how this can translate into a really big global impact for these species,” says Pierce-Higgins.

Added Stress Factor

Many seabirds that are contracting the virus live a long time and reproduce slowly. Skuas take about seven years to reach maturity and lay two eggs a year. The gannets only laid one. This means that any recovery of the population will be inherently slow.

“It’s an effect that will be seen for decades,” Pierce-Higgins says. Pierce-Higgins likens this outbreak of avian flu in seabirds to the devastating decline in populations of bald eagles, peregrine falcons and many other birds of prey due to DDT poisoning, which American author Rachel Carson brought to the public’s attention. silent Spring 1962. The ubiquitous pesticide was contaminating food webs, thinning birds’ shells and killing their embryos. “The priority is to understand what’s left,” Pierce-Higgins says.

The now shrinking seabird population from bird flu is already under threat from many other threats. With the combined threat of climate change, over-fishing of their prey, bycatch in fisheries, and the combined threat of non-native predatory mammals such as rats and cats eating their eggs and chicks, more than half of seabird species are in decline. is believed.

In addition to being watchdogs for the health of the oceans, seabirds also play an important role in marine and terrestrial ecosystems. They carry essential nutrients in their feces, and as apex predators in the ocean, many species of seabirds help regulate the rest of the food web. Just as there is a shortage of sharks in the ocean, when they are in excess, the decline of seabirds can also have a major impact and upset the balance of ecosystems, including those that support major fisheries. .

“We’ve been talking for a long time, as have many conservationists, about the decline of seabirds and their pressures,” says Kevin Kelly of the RSPB. “It’s something new that wasn’t on the radar.”

a response strategy

The big question unanswered at this time is what will happen. So far, there has been only one asymptomatic report of this avian flu strain jumping to humans, although the potential for zoonotic outbreaks in the future remains.

For wildlife, a worrying prospect is that migratory seabirds will transfer this transmissible new form of the virus to greater populations, particularly in the Southern Hemisphere, which has so far remained largely unaffected.

It is not yet clear which species can carry the virus asymptomatically. James Pierce-Higgins believes that one group of birds in the UK that may act as a vector for the virus are seagulls.

“They occupy a lot of wetland areas where some of these waterfowl may have been and then potentially go to seabird colonies to breed,” he says. The last winter census of the gull population in Britain was in 2006, and Pierce-Higgins hopes the emergency will help raise funds to repeat the surveys this year.

Meanwhile, according to Ruth Cromey, there is an urgent need to implement national and regional response plans before more outbreaks occur in wild birds.

Possible strategies they suggested include not building poultry farms near wild bird colonies, keeping dog walkers out of critical areas, and creating no-fly zones to prevent bird stress during nesting. Officials also need to know whether it is a good idea to raise bird carcasses, a question that has remained unclear during the current outbreak.

“These are not the last crises that are going to happen on our increasingly polluted planet with all these different interfaces between wildlife and people,” he says.

So far, most of the attention has focused on virus surveillance among domestic birds. Many conservationists and scientists advocate for much funding to study the spread of the virus among wild birds.

Kelly hopes the avian flu crisis will help governments put more money into conservation programs that help reduce clear and pre-existing threats to sea birds so they have the best chance of recovery.

On Shetland, locals anxiously wait for the end of the breeding season and seabirds to disperse from their nesting sites in the hope that it will bring temporary relief this year.

“I want this season to be over and the birds are gone, to try and finish it,” says Shetland Seabird Tours manager Phil Harris. “Then we’ll see what comes next year.”

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