July 8, 2014, by Tim Radford
Early bird: a chick of the Arctic migrant, the red-necked phalarope
Image: US Fish and Wildlife Service via Wikimedia Commons
As global warming increasingly causes Arctic snow to melt earlier, researchers warn that it could have a long-term adverse effect on the breeding success of migrant birds. LONDON, 8 July, 2014 − Arctic migrants are nesting up to seven days earlier as the world warms. The sandpiper makes a beeline for the Alaskan shores, to join the phalarope on the beach and the songbirds in the woods − and all because the winter snows are melting earlier. Conservation scientists Joe Liebezeit and Steve Zack – both then of the Wildlife Conservation Society (WCS) – and colleagues report in the journal Polar Biology that they looked into nearly 2,500 nests of four shorebird species in Alaska – two sandpipers, two phalaropes − and a songbird called the Lapland songspur over a nine-year period.
They recorded when the first eggs were laid. And they also assessed snow melt in nesting plots at different times in the early spring, and took note of predator abundance and the seasonal flush of vegetation − both of which can affect nest timing − to see what mattered most in terms of breeding. “It seems clear that the timing of the snow melt in Arctic Alaska is the most important mechanism driving the earlier and earlier breeding dates we observed in the Arctic,” said Liebezeit, now of the Audubon Society of Portland, Oregon. “The rates of advancement in earlier breeding are higher in Arctic birds than in other temperate bird species, and this accords with the fact that the Arctic climate is changing at twice the rate.” During the nine years in which the scientists conducted their study, they found that nesting advanced by between four and seven days. “Migratory birds are nesting earlier in the changing Arctic, presumably to track the earlier springs and abundance of insect pray,” said Steve Zack, who is the WCS co-ordinator of bird conservation. “Many of these birds winter in the tropics and may be compromising their complicated calendar of movements to accommodate this change. We’re concerned that there will be a threshold where they will no longer be able to track the emergence of these earlier springs, which may impact breeding success or even population viability.”
The calendar of Arctic life is shaped by ice, and the ecology of the region is beginning to change as the area of sea covered by ice shrinks with successive summers. But Ingrid Onarheim, of the University of Bergen’s Geophysical Institute, and colleagues warn in the journal Tellus − published by the International Meteorological Institute at Stockholm University − that the Arctic ocean is losing ice even in winter, at least north of the island of Svalbard, Norway. A study of satellite records shows that this region is losing winter ice at the rate of almost 10% per decade, and the north Atlantic water that enters the Arctic ocean at this point has been warming at 0.3°C per decade. At the same time, the surface air temperature has been warming at 2°C per decade, and researchers have recorded an average rise in winter temperatures of 6.9°C in the last 34 years. They believe that winds have not caused the long-term warming or loss of ice, so it must be warmer ocean temperatures pushing into the region west of Svalbard. The ice, furthermore, has thinned with the decades, making it more likely to melt and retreat with each succeeding winter. – Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.