Previous outbreaks of avian influenza occurred mainly in wintering areas of wild birds, after which the disease subsided at the end of winter. But when the virus emerged this year in seabirds that had recently arrived on their summer grounds in the Shetland Islands, local experts knew something strange was happening.
“Alarm bells started ringing immediately, because the speed with which the virus spread before the breeding season this time was terrifying,” Kelly said.
H5 avian influenza viruses are constantly developing new strains, which can spread simultaneously between the same host. In the decades since the virus emerged, it has mutated and recombined countless times, but until now, transmission of the avian influenza virus has not been effective enough to cause major outbreaks.
“What we’re seeing with this particular alternative is that it appears to be more transmissible,” said Ruth Cromey, wildlife advisor to the Convention on Migratory Wildlife Conservation.
It is not yet clear how this infectious strain of the virus is transmitted from winter to spring, but the new strain poses a significant threat to populations that congregate in overcrowded breeding colonies.
Scotland has about half of the world’s gannet breeding colonies. The janet is the largest seabird in the North Atlantic and is closely related to tropical birds. The Shetland Archipelago is a real stronghold of these birds, the islands are located on the edge of the continental shelf of Europe, where the turbulent sea is very productive and rich in food.
Visitors who take a boat trip from Lerwick, the capital of the Shetland Islands, to Noss Island in mid-July enjoy a remarkable sight: thousands of gannets nest on sandstone cliffs that rise nearly two hundred meters perpendicular to the sea. In the air above the island, there is the coming and going of the flying birds, which are in a cacophony of loud screeching and shooting in all directions like arrows in the sky. Every now and then, the wind bore the fishy smell of guano from the dried white feces that drooped like stalactites from the narrow ridges of the cliffs.
But if you survey the colony with binoculars, you will see that many crumpled birds – dead gannets – are located between the nests. At the foot of the cliffs the waves collected the carcasses of animals in white rafts. A little later, a species of predatory gull – a type of predatory gull – feeds on one of the floating carcasses.
There were periods in the spring and summer when the carnage was hard to overlook. Phil Harris, a nature guide who takes visitors to the breeding colonies of Noss, describes how to sail his boat through floating rafts made up of fifty or sixty ferrets.
“In three cases, even a dead gannet fell into the sea next to the boat, and it fell off cliffs somewhere,” he says.
contaminated food chain
Other alarming changes have been observed in the birds’ behavior. In Scotland, about 60% of the world’s population of predatory gulls, known for their aggressive behaviour, breeds by diving at anyone who dares to approach their nests or try to steal a meal from other birds.
Usually in Noss, Harris sees bands of great fishermen chasing gannets and forcing them to hand over caught fish. “But you don’t see that now,” he says, “probably because there are a lot of dead gannets floating around for the hunters to feed on.”
In some cases, large seabirds begin to display neurological symptoms within hours of infection: As the virus multiplies in their brains, fishermen become increasingly disoriented and eventually succumb to multiple organ failure. Shetland gannets have been seen sitting helplessly on the beach and seemingly blind. After their carcasses are handled by large hunters, the spread of the virus becomes so obvious that large, predatory gulls can sometimes be seen circling in full flight.
“It’s sad to see, because they’re usually such cruel beasts,” says Kevin Kelly. A wild bird of prey that could no longer stay in the air. The neurological effects are enormous.
At the level of the entire population, the situation is even more alarming. In several places in Scotland, the number of large skuas has been halved compared to last year. At some of these sites, only about a dozen birds remain. James Pearce-Higgins has received similar reports of mass deaths among great skuas on other Scottish islands. If current trends continue, this species could become extinct within a year or two.
So far, reports on gannets have been less bleak, but in some colonies, a quarter of all adult birds died during this breeding season.
Elsewhere, entire breeding colonies have vanished from the face of the earth, including the sandwich artichoke in Texel in the Netherlands. Hundreds of Dougal terns have died on Coquette Island, one of Britain’s rarest seabird colonies. “Very soon you’ll see how all of this could have global implications for these species,” Pierce Higgins says.
Additional stress factors
Many seabirds that contract the virus are long-lived and slow-breeding animals. Large skuas are sexually mature only after seven years and lay no more than two eggs per year. In fact, gannets only produce one egg per year. This means that the population can recover normally only slowly.
“We’re dealing with an impact that will be felt for decades to come,” says Pearce-Higgins. He likened the outbreak of avian influenza among seabirds to the catastrophic decline in the number of bald eagles, peregrine falcons and countless other types of birds of prey as a result of massive DDT poisoning, a crisis that began in 1962 with the famous book. silent spring By journalist Rachel Carson it was brought to the attention of the general public. The widespread use of pesticides contaminated entire webs of food chains and prompted the birds to lay eggs with extremely thin shells, causing their embryos to die. “It’s now important to explore what’s left,” said Pierce Higgins.
The seabird populations now decimated by bird flu faced many threats before then. It is estimated that more than half of all seabird species in the world are declining in number due to a combination of factors. These include climatic changes and overfishing of the species of fish that birds feed on. Seabirds are often unintentionally killed as bycatch and threatened by non-native predators such as cats and mice, which feed on bird eggs and chicks.
Seabirds are an outstanding species that reflects the health of the world’s oceans and plays a vital role in terrestrial and marine ecosystems. Their droppings transport important nutrients through ecosystems, and as marine apex predators, they make an important contribution to the organization of an entire web of food chains.
Just as the lack of sharks from overfishing has significant impacts on ocean ecosystems, the decline in seabird numbers is likely to disrupt the balance of other ecosystems, including important fishing sites.