“What we found with this particular strain of the virus is that it appears to be transmitted much more efficiently,” says Ruth Cromie, wildlife health adviser at the Convention on the Conservation of Migratory Species (Bonn Convention).
We still don’t know how this new form of the virus made its way from winter to spring, but it puts seabird populations at particularly high risk when they gather in dense breeding colonies.
Scotland is home to about half the world’s population of boobies, the largest seabirds in the North Atlantic. The Shetlands are traditionally a stronghold of these species, mainly because the proximity of the continental shelf to Europe makes the surrounding waters very productive and rich in food.
In mid-July, visitors traveling by boat from Lerwick, the capital of Shetland, to neighboring Noss Island, marvel at the thousands of boobies that nest on the narrow edges of the 180-meter-high sandstone cliffs. Above their heads, birds fly away like arrows and cut their way through the noise of hoarse cries. From time to time, the wind releases effluvia of guano, coming from the stains that decorate the cornices like stalactites.
If we look more closely through binoculars, however, we can see the remains scattered among the nests. At the foot of the cliffs, the water currents piled up white mounds of freshly fallen bodies. A little further on, a large skua is feasting on one of the boobies floating in the water.
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In spring and summer, the devastation is sometimes even more evident. Phil Harris, a tour guide who takes visitors to Noss’s seabird colonies, says he maneuvered his boat between the floats of fifty or sixty boobies.
“Three times, dead adult birds appeared from the cliff and dropped dead beside the boat,” he said.
THE INFECTED FOOD CHAIN
Other worrisome changes affect bird behavior. Scotland is home to around 60% of the world’s population of large skuas, notoriously aggressive birds that will bomb anyone who dares to approach their nests and harass other birds for free meals.
Typically, on the Isle of Noss, Harris observes flocks of large skuas chasing boobies and forcing them to regurgitate their catch. “You don’t see that anymore, probably because there are so many dead lunatics they can feed on.” »
In some cases, within a few hours, the birds begin to show neurological signs of infection. They are increasingly disoriented as the virus replicates in their brains and various organs begin to decline. In Shetland, boobies were seen lying helpless on beaches, appearing to have lost their eyesight. Once they get rid of the carcasses, the infection of the large skua is evident, with some spreading through the air.
“It’s heartbreaking to see when they’re usually so full of spirit,” saddens Kelly. “We have this big bully who can no longer hold his head up. It affects them a lot neurologically. »
The situation is even more worrying at the population level. Large numbers of skua on sites in Shetland have dropped by at least half compared to the same period last year. In some areas, only about one in ten birds survives. James Pearce-Higgins has heard similar reports of major skua deaths on other Scottish islands. If the current situation continues in this direction, the species could be a year or two away from extinction.
So far, reports of boobies are not so dire, but in some colonies up to 25% of adults have died during this breeding season.
Elsewhere, entire breeding colonies are being wiped out, including sandwich terns on the island of Texel in the Netherlands. Hundreds of rosy terns have died on Coquet Island, the UK’s rarest seabird colony.
“Very quickly, you can imagine the really significant consequences this could have on a global level for these species,” worries Pearce-Higgins.
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LONG TERM CONSEQUENCES
Many seabirds that contract the virus are long-lived, slow-breeding birds. Large skuas take about seven years to reach maturity and lay two eggs a year. Boobies only put one. Therefore, any rebuilding of populations is bound to be slow.
“We are facing an impact that will be felt for decades,” says Pearce-Higgins. The scientific director of the British Trust for Ornithology compares this epidemic to the devastating collapse of populations of bald eagles, peregrine falcons and many other raptors due to DDT poisoning, which American author Rachel Carson revealed to the public in her book silent spring, published in 1962. This ubiquitous pesticide has contaminated food webs, diluted the birds’ protections and killed their embryos. “So the priority is figuring out what’s left,” says Pearce-Higgins.
AND NOW ?
The big question, still unanswered, is what will happen next. Currently, only one case of transmission of this strain of avian influenza to humans has been reported, and it was asymptotic, but future zoonoses remain possible.
In wild species, the worrying prospect is that migratory seabirds will transmit this new transmissible form of the virus to other populations, particularly in the southern hemisphere, which remains largely spared at the moment.
It is not yet known which species can carry the virus asymptomatically. According to James Pearce-Higgins, a group of birds in the United Kingdom could serve as a vector for the virus: seagulls.
“They occupy many wetlands where some of these waterfowl have been and potentially move into seabird colonies to breed,” he explains. The last winter census of UK gull populations was carried out in 2006, and Pearce-Higgins hopes this emergency will secure the funding needed to carry out more research this year.
However, it is urgent, according to Ruth Cromie, to put in place national and regional response plans before other epidemics reach wild birds.
The expert suggests, in particular, not to build farms near colonies of wild birds, to prevent people who walk with their dogs from accessing certain important areas and to create no-fly zones to avoid stress to the birds during nesting. Representatives should also consider whether or not it would be wise to collect poultry carcasses, an issue that has yet to be decided for the current outbreak.
“These are not the last crises that will occur on our increasingly polluted planet, with all these different interfaces between wildlife and humans,” he predicts.
At the moment, attention is mainly focused on the search for the virus in domestic birds. Many conservationists and scientists are advocating much more funding to study the spread of the virus in wild birds.
Kelly hopes the avian flu crisis will help convince governments to allocate more funds to conservation programs that will reduce the obvious and pre-existing threats to seabirds, to give them the best possible chance of survival.
In the Shetland Islands, residents nervously wait for the breeding season to end and seabirds to leave their nesting grounds and disperse, bringing temporary relief to this year.
“I want this season to end and the birds to be gone, to try to end this situation,” says Shetland seabird tour guide Phil Harris. “Let’s see what comes next year. »