What happens in the Arctic, doesn’t stay in the Arctic: change flows south of the Arctic Circle as an altered jet stream brings extreme weather to middle latitudes, some scientists say. It also rises, as thawing permafrost leaks CO2 and methane into the atmosphere, heightening global temperatures. And, more and more, it flies out of the North, into temperate and tropical ecosystems, as migratory birds are impacted adversely by a hotter Arctic climate.
In recent years, climate change-affected migratory species have become a major focus of the Arctic Council’s Conservation of Arctic Flora and Fauna subgroup, and the United Nations Convention on Migratory Species. Both are trying to determine not only how climate change is altering Arctic ecosystems, but how those shifts are impacting ecosystems to the south, with migratory animals – especially birds – acting as a kind of vector of transmission.
One major problem they’re looking at: the rapidly warming Arctic has resulted in dramatic changes in plants and the makeup and timing of insect hatches, meaning that birds reliant on a particular Arctic food supply are often now departing the North on long migratory journeys with less stored energy than in years prior.
“The Arctic is very important for shorebirds and waterbirds, like geese and ducks, and some species of seabirds, like terns,” says Borja Heredia, head of the avian unit at the UN Convention on Migratory Species. “All of these creatures use the Arctic. But the ice is melting, the conditions are changing, and the timing of migration is being affected by climate change.” Migratory birds that spend their summers in the Arctic have winter destinations as far away as the forests of Central America and the Amazon basin, or the shores of West Africa – which makes the conservation of stopover habitat all the more important.
The red knot (Calidris canutus) is a scientifically documented example of a climate change-impacted migratory species. Flocks of these shorebirds, a medium-sized sandpiper, fly 15,000km (9,300 miles) north, from wintering grounds on the Mauritania coast in West Africa, to the high Russian Arctic. There, as the snow melts, the birds mate. Once the chicks emerge from their eggs, they spend two months gorging on insects, fattening up for the long voyage back to Africa. Or at least, that’s how it used to work.
“Due to Arctic warming, the juvenile red knots are still making it to West Africa, but by the time they arrive they’re so small they have a problem getting food out of the sediment,” says Jan van Gils, a marine ecologist at the Royal Netherlands Institute for Sea Research. In a 2016 study in Science, Van Gils found that the young birds have shrunk by about 15 percent since 1985. Part of this shrinkage includes a smaller beak which jeopardizes their survival. Red knots eat bivalves buried about three to four centimeters in the sand, but now their beaks are often too short to reach such depths, and the birds are forced to subsist on less nutritious seagrass instead.
As a result of this problem, along with other stressors especially habitat loss, redknots are listed as Near Threatened by the IUCN.
Scientists hypothesize that the red knots’ shrinking size is likely due to a trophic mismatch in the Arctic breeding grounds. “Because they are migratory, they have difficulties keeping up with the rates of change in the high Arctic, especially in their own food supply,” says Van Gils. With the snow melting earlier and earlier, insects are emerging ahead of schedule, while the birds’ arrival and hatching dates have stayed the same. As a result, the red knots’ reproduction schedule is now mismatched with peak food availability, and the chicks grow without an adequate protein source.
This North-originating problem “might even lead to a vicious cycle where, once they’re smaller, they cannot feed on bivalves in West Africa and have to switch to seagrass, which is harder to fuel up on, [making it] harder to leave earlier for Russia to get the insects.”
Of greater concern, this phenomenon isn’t likely limited to red knots. A number of species around the world are shrinking in body size due to global warming, impacting their ecosystems in various ways. For migratory species, these impacts are doubled.
Heredia emphasizes that regional climate change effects on migratory species can be a two-way street. “These impacts happen in one direction and the other direction [too] … Many of these [Arctic] species will go into the tropics, and there you have deforestation,” along with escalating drought and other climate change precipitated stressors. There are problems for long distance migrators at mid latitudes too.
A 2014 study, for example, found that climate change exacerbates the risk of extinction for nearly 90 percent of North American shorebirds, all of which are migratory. Researchers detected global warming risks in tropical wintering and Arctic summering grounds, and along migratory routes – including shrinking tundra; rising sea levels; increasingly stormy, extreme weather; ocean acidification; and alterations to specialized environments, such as the temperate stopover havens where migrants rest.
For North American red knots, this makes for multiple climate change-induced pressures all along their routes. Beside shrinking nesting grounds and a food shortage in the Arctic, the birds must also face warming and acidic oceans that inhibit the growth of shellfish (another important high-energy food source); rising sea levels that can degrade and flood flyway marshes; plus altered nesting and stopover habitat that can expose them to more predators.
“Migration is a risky adventure,” says Heredia. “If birds are not well prepared, they’ll have a lot of problems.”
One solution: scientists and policymakers are now rallying nations along migratory flyways to conserve stopover habitat that provide avian species with a place to shelter, feed and rest.
Later this year in the Philippines, the Convention on Migratory Species will convene the parties in hopes of passing an agreement to protect the East Asian-Australasian flyway, a route that stretches from the Taimyr Peninsula in Russia to Alaska, and southward to Asia, Australia, New Zealand and finally Antarctica. An estimated 55 migratory species travel along this route, with about 5 million birds using it per year.
Other migratory routes, summering and wintering grounds, urgently need to be assessed and protected. “From a conservation perspective, it’s very important to look at the whole itinerary of [a migratory bird species], not just one country or ecosystem,” says Heredia. “If we destroy these stopover sites, then forget it. It’s the end of the story.”