Many pairs of golden eagles summer on breeding grounds in the high northern latitudes of Alaska and Canada.
“The goldens move out with the onset of colder temperatures and the reduction of prey availability,” said Bryan Watts. “They migrate south to winter in southern latitudes where prey availability remains high during the winter.”
But climate change has thrown a wrench into that age-old migration pattern. And it’s not just golden eagles. Watts, the director of William & Mary’s Center for Conservation Biology, and Fletcher Smith, a research associate at the CCB, are part of an effort to share animal-tracking data to get a handle on what is ahead for the diverse animal populations of the changing Arctic and near-Arctic habitats.
Watts and Smith are among the authors of a paper, “Ecological insights from three decades of animal movement tracking across a changing Arctic.” The paper was recently published in the journal Science, announcing the establishment of the Arctic Animal Movement Archive. The AAMA is a compendium of more than 200 standardized tracking studies going back some 30 years.
“This paper is really about the importance of establishing collaborative data sharing to answer questions that are larger or beyond what the data were originally collected for,” Watts explained.
The Science paper focuses on changes in the migration patterns of caribou and golden eagles, but the AAMA is concerned with studies tracking the movements of a full range of Arctic-using species, from bowhead whales to moose to bears. In addition to the golden eagle data, the CCB has also contributed data from other migrant bird species, including bald eagles and whimbrels, to the AAMA database.
“Golden eagles were just pulled out from a list of many species as a case study, or example,” Watts said. “They are a good fit for a climate change study because they migrate from northern to southern latitudes of North America and their breeding season is highly restricted by summer climate, and by available prey, which itself is influence by climate.”
He added that golden eagles are a species of high conservation concern, and therefore it is important that conservation scientists understand what might be ahead as the birds try to adapt to a changing climate, especially in their Arctic summering grounds. Prey availability is among the top climate-related concerns for the species, he added.
“Golden eagles could face changing conditions in prey availability along migration routes,” Watts explained. “That might impact breeding preparedness. The birds could also face changes in prey populations within traditional breeding areas if warming and drying continue beyond some tipping point in the future.”
The Science paper notes that the Artic is experiencing a variety of changes, including ice loss, earlier spring snowmelt and warmer winters. The AAMA database shows a number of responses to the changes by Arctic fauna. Other wildlife species are experiencing the changes in predator-prey relationships mentioned by Watts. A rapid northward shift in ranges also has been observed.
The CCB’s golden eagle data were combined with other studies, making a total of 103 birds tracked via satellite transmitter. They noted arrival times of the birds at their summering grounds and modeled that data with other factors, including the Pacific decadal oscillation index, or PDO. The PDO is based on the temperatures of surface waters in the Pacific Ocean, and is a major driver of climate in western North America.
“Warm phase” PDO winters bring higher temperatures and reduced snowpack. The paper notes that after 2011, the PDO became a more important predictor of arrival dates of eagles than other factors. They found that over 25 years the eagles began summering at earlier and earlier dates.
Watts stressed that the value of the AAMA comes from the combining of work on numerous species by numerous scientists. The combination of studies allows scientists to take that 25-year-long look at eagle summering dates.
“We have collected golden eagle data from maybe 2008 through 2015 so this data was merged with other tracking projects to gain a longer-time view,” Watts said. “This is the benefit of many projects being merged to generate a larger dataset capable of addressing either longer-term or larger-scale questions.”