Ferruginous hawks challenged by climate change
Thursday, Feb 27, 2014 06:00 am
If we learned anything from Sesame Street, it’s the bigger the bird, the bigger the nest.
And like that giant yellow canary, Big Bird, the rust-coloured ferruginous hawks, the largest hawk in North America with its nearly metre-and-a-half wingspan, is no exception.
Ferruginous hawks like to build, and over the years their remarkable nests can grow into towering pillars of sticks, grass and dried mud, some of which – at least the cliff-side nests – can reach sizes of two metres high by two metres wide.
But with a changing climate and an increasing frequency of severe storms it appears these big nests may be a liability, yet one more challenge for a species that is already in decline. The ferruginous hawk, which is primarily found in the prairies, is listed as a threatened species in Canada. In Alberta, the hawks are classified as endangered with 643 nesting pairs in 2010, down from 1,791 in 1987.
Chief among the odds stacked up against ferruginous hawks is habitat loss, but climate change appears to be having dire consequences on one of the West’s iconic raptors.
Ryan Fisher, project co-lead of the Biodiversity Management and Climate Change Adaptation project and former post-doctoral fellow with the University of Alberta’s Raptor Ecology and Conservation team (REACt), said wind blowouts are proving to be the single largest factor in nest failures.
“We definitely do know the wind blowouts of the nests are one of the largest sources of nest failures, so when we look at all the nests that failed or are damaged or are able to be used again in a subsequent summer, wind blowouts or trees getting knocked over is definitely the No. 1 source,” Fisher said.
Janet Ng, a PhD candidate and ferruginous hawk researcher at the U of A, said the larger the nest, the more susceptible it might be in extreme weather events.
“Their nests have withstood storms for decades,” Ng said, “but at the same time they use mud and grass to get it to stick together and the bigger they get, they get heavy when they get wet.
“It could either be the most bomber nests out there (have) stood for the length of time they’ve been out there, or in time they could be a lot more susceptible because they are so much bigger and heavier.”
The hawks, however, aren’t being left out in the storm. Instead, the U of A is working with the Alberta Biodiversity Monitoring Institute (ABMI) and the Miistakis Institute to understand how climate change is affecting ferruginous hawks and how we might be able to help them cope.
“We are really about providing decision makers with what they need to make decisions and understanding how climate change, understanding the effect of climate change on our species and ecosystems is another piece of information in the land-use decision-making puzzle and it is one understanding climate change and impacts on biodiversity is in its infancy in land-use decision-making,” said Amy Nixon, ABMI’s climate change project co-ordinator.
“The hawk project is really identifying the effects of extreme weather events, which are predicted to increase in frequency with climate change in Alberta,” Nixon said. “The second step is to identify potential strategies to mitigate the potential negative effects on the hawks.”
One of those strategies – artificial nesting poles – has already been in use for 20 years and it appears the poles are less likely to be affected by high winds, providing hawks with a secure nesting site.
Fisher said preliminary results suggest nesting poles provide a robust nesting site that is twice as likely to protect ferruginous hawk nests over trees.
“We think it is a good potential tool. We do have to do some more work in terms of where we should put these artificial nesting platforms,” Fisher said.
One of the outcomes Fisher is hoping to see from the study is to get a better understanding of the best-possible location, design and critical mass, so the number of hawks in a region is not greater than the available food, especially given the growing scarcity of native grassland.
However, even though the hawks do use the nesting poles, they are still in decline, Fisher said.
“Whether or not we’re seeing some of the effects of migration in the winter influencing populations of hawks in Canada, that is one thing we’re not too sure about. We’re hoping to use that, it is probably a future project, to try and identify where these birds are wintering and where they are migrating through and hopefully we might be able to tease apart what might be happening down there to Canada’s population,” Fisher said.
As part of the project, Fisher, Ng and the other members of REACt monitor approximately 300 nests a year, tracking the number of eggs laid in spring and how many chicks survive to fledge and leave the nests.
The team also uses portable weather stations to see how the storms correlate with all of the data, including territory and chick survival and satellite transmitters mounted on a few of the hawks to help the researchers better understand the size of territory each mated pair needs, where they hunt and how far they will travel from the nest. It also provides some clues as to what happens to the hawks during the migration.
The prairies with its long and short grass is one of the most endangered ecosystems in the world, Ng said, with only about 20 to 30 per cent of untouched prairie left throughout North America. In Alberta, roughly 40 per cent of native prairie is left and only 20 per cent in Saskatchewan.
But as ground squirrels are the major food source for ferruginous hawks, they tend to do well where the squirrels do well and in the West that is agricultural land, especially ranchlands.
And that is good news for ranchers and for hawks. A single ferruginous hawk family will eat four or five ground squirrels a day over a three-month period and as a result, Ng said ranchers who do have ferruginous hawks nesting on their land tend to be protective of the birds and willing participants in the study because they want to see the hawks endure.
Along with a greater understanding of the design of nesting poles, both Fisher and Nixon said the larger goal of the project is to provide provincial and federal regulators and land managers with tools to make decisions that will benefit the hawks and other species at risk.
“The hope is the project will bring some strategies for the province for managing species at risk under climate change and I think that it hasn’t necessarily been ignored, but it is not at the top of people’s plates in terms of what is influencing these species. It is important to get the message out there that not only will habitat loss cause decline of these species, but also the change in climate but specifically extreme weather,” Fisher said.