A new study underscores the climate threat to Arctic breeding birds, while also emphasising how important habitat conservation will be to preserve their shrinking breeding grounds.
Each Arctic summer hundreds of millions of birds arrive in the tundra, to spend long days breeding in this vast treeless plain between polar deserts to the north and the tree line to the south.
Yet as the climate warms, the tree line is expected to march north, radically reducing breeding habitat for many birds reliant on open, tree-less tundra. In fact warming is already “shrubifying” the tundra, beckoning northward red foxes and other predators of vulnerable breeding birds.
The new international research by the University of Queensland’s Hannah Wauchope and colleagues focuses on 24 Arctic-breeding shorebirds. Climate change, they find, could cause suitable breeding conditions for these migratory birds to collapse over the next 70 years, as suitable conditions shift, contract and decline. Up to 83% of the species could lose the majority of currently suitable breeding area.
For one long-distance migrant, the red knot (Calidris canutus), breeding habitat could shrink down to a paltry 5 to 12% of its current area.
Showing the complex ways in which warming causes harm, the red knot’s survival is already decreasing. These birds suffer malnutrition in years with early snow melt in their high-Arctic breeding grounds, the fastest-warming region in the world. The malnourished young birds have smaller bodies and shorter bills. After the trip south to their tropical wintering grounds, these smaller birds can’t forage as well (their ideal food is deeply buried bivalves), so fewer survive the winter.
In general, warming will mean fewer birds of many species making the return trip to points south, where we can enjoy them on our shores. Many Arctic migrants travel more than 20,000 each year. The bar-tailed godwit makes remarkable non-stop Alaska-New Zealand flights of up to 12,000 kilometres, a remarkable avian feat that has astonished biologists.
As the climate warms, the new study predicts, breeding migratory birds will increasingly need to retreat northward, to small Arctic Ocean islands. Some birds might even need to change their migratory pathways to sustain connections to suitable habitat.
Yet many experts question whether some long-distance migratory shorebirds can do this. They have well defined migration routines, often tightly choreographed to capitalise on transient feeding conditions at specific stopover points, as well as migration endpoints.
For example, in Winged Sentinels we describe how the rufa subspecies of red knot time its journey from Tierra del Fuego to the Arctic to arrive in Delaware Bay on the US mid-Atlantic coast during the brief horseshoe crab breeding season. When they arrive, the birds are bundles of feathers and bone, but double their weight feeding on the energy-rich crab eggs in just a couple of weeks, becoming so fat they appear to waddle. Shorebirds’ tight schedules and very conservative migratory behaviour augers ill for flexible responses to climate change.
At the same time warming is increasing human activity in the Arctic. “Climate change is also opening up the Arctic to threats such as mining and tourism,” Wauchope said in a statement,” and we must make sure we protect key places for all Arctic species, including these amazing migratory birds.”
The research paper cited a lack of protected areas in Canada’s Arctic, where resource extraction is a growing threat to birds and other wildlife.
Wauchope HS et al. (2016) Rapid climate-driven loss of breeding habitat for Arctic migratory birds. Global Change Biology.
University of Queensland (2016) Birds on top of the world, with nowhere to go. Media Release 20 July.
van Gils JA et al. (2016) Body shrinkage due to Arctic warming reduces red knot fitness in tropical wintering range. Science.