Studying the Mysteries of Migration

There are still many questions about bird migration, including how it’s affected by climate

Millions of birds make their way through the San Francisco Bay Area on the way north to their breeding grounds every spring. Many shorebirds and waterfowl have already left, and now waves of songbirds are passing through. As well-watched as birds are, there are still a lot of things scientists don’t know about migration, including precisely where different species go each summer and winter, and what exactly triggers them to get going. Since so many birds pass through here, the Bay Area is a good place to try and sort out some of the questions, and to try to tackle another: how does climate change affect birds?

The San Francisco Bay Bird Observatory, a non-profit science and conservation organization, has been monitoring birds here for 30 years. The information collected through its bird banding program, has helped reveal some of the likely effects of climate change on birds. For example, a paper released last year suggests that climate change is making some species larger.
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Mapping California’s Shifting Climate

By Gretchen Weber & Molly Samuel

A companion radio piece to this post aired on The California Report.

Map from The Nature Conservancy showing projected drought conditions for 2070-2100

Projected drought conditions for 2070-2100 (Map: The Nature Conservancy)

Climate change is causing conservationists to rethink traditional methods of protecting lands and ecosystems. The conventional strategy of setting aside a specific parcel of land (and increasingly, ocean) to protect a particular community of organisms may no longer be sufficient in a rapidly changing climate. While greenhouse gas reduction and climate change mitigation remains a top priority for most conservationists, land managers have begun developing adaptation strategies that take the effects of a warming planet into account.

“We have a fantastic conservation success story in having conserved a huge network of protected areas,” says Healy Hamilton, director of the Center for Applied Biodiversity Informatics at the California Academy of Sciences. “The issue with those protected areas is that they all have static boundaries around them and they work to protect what lies within them,  So the plants and animals that are there are well-protected, as long as they stay there.” Trouble is, the habitat isn’t staying put.

Climate has “Velocity”

The world’s ecosystems will need to move about a quarter of a mile each year to keep up with climate change, according to a recent study published in Nature (link is to the first paragraph of the paper; the full article is only available to subscribers, but you can read a press release about the about the study).

Researchers from the Carnegie Institution, Stanford, the California Academy of Sciences, and UC Berkeley collaborated on the paper, which describes climate belts sweeping north and south from the equator–and also moving uphill–as the world warms.

Hamilton, who co-authored the study, told a packed house at the Center for Biological Diversity in January, that “Climates are on the move. It’s not just a slow unfolding, it’s a radical, abnormal process. Everywhere we look, shifts are already occurring.”

And under these changing conditions, she said, plants and animals have three choices: “They can stay and adapt, they can shift with their climate, or they can go locally extinct if they can’t move fast enough.”

The study’s lead author, Scott Loarie, a fellow at the Carnegie Institution, explains that climate change forecasts are commonly measured in degrees per year, but the authors of this study wanted to know how those temperature changes would affect what can live where. So they used temperature “velocity” (in kilometers per year) to measure how fast regional climate conditions are moving as the planet heats up.

It turns out that the belts move at different rates, depending on the landscape. In the Amazon Basin, velocity is relatively high. It’s a large and homogeneous ecosystem, so as the temperature changes there, plants and animals will have to travel a long way to keep up with the climate in which they’ve evolved to thrive. In a place like California, with its microclimates and variable topography, the velocity is lower. Some species may need merely to migrate to a nearby north-facing–and therefore cooler–slope. Others will have to head north and toward the coast. Climate models forecast that eventually the Bay Area will look more like Southern California, and the Bay Area’s current climate will be located somewhere north of us.

Projected Heat Stress in California for 2070-2100 (Map: The Nature Conservancy)

Projected Heat Stress in California for 2070-2100 (Map: The Nature Conservancy)

Mapping a Moving Climate

The Nature Conservancy of California has attempted to map some of these trends (see above and below). Scientists averaged together several different climate models to create a picture of California’s future in terms of temperature and precipitation. They then applied that projection to habitats for specific species, to make predictions about how ranges may shift. The maps show both how much areas are likely to change, as well as how certain the predictions are.

“What we’re trying to understand is how does the way we protect species in the future need to change with a changing climate,” says Rebecca Shaw, Director of Conservation for the Nature Conservancy of California. “The kind of strategies you employ and how much you spend is really going to be dependent on how certain you are about change in the future.”

For example, she says some parts of the Sierra are not likely to change very much over the next century, but some places like the Mojave Desert are expected to change a great deal. That kind of information could be useful for land managers trying to plan for the future. For example, in areas that are expected to undergo great change, it might be more important to preserve corridors, or connecting stretches of protected lands, so that populations can move as the climate changes, if they are unable to adapt where they are.

Loarie says “assisted migration”–helping specific species move to new locations–is expensive, unpredictable, and unrealistic. Instead, he, too, corridors for plants and animals to safely follow their climate–if they can keep up. Species like the American pika, already living on mountaintops, can’t go any farther uphill. Their habitats could disappear completely, or, as Loarie says, “they’ll pop off the top.”

There are limitations to the predictions one can make with temperature velocity measurements. What temperature changes will do to fog, for instance, is still unknown, so it’s not clear yet where the redwoods will need to move in the next 100 or so years.

To enable the second option, Hamilton agrees with Loarie. she says the conservation community needs to rethink its traditional strategy of protecting lands. Instead of protecting specific parcels of land and expecting them the stay the same over time, conservationists need to expect change, and to create connectivity in the landscape so that species can move when and if they need to.

Projected changes in California Salamander habitat (Map: The Nature Conservancy)

Projected changes in California Salamander habitat (Map: The Nature Conservancy)

Projected changes in California Blue Oak habitat (Map: The Nature Conservancy)

Projected changes in California Blue Oak habitat (Map: The Nature Conservancy)

Major Shifts in California Bird Movements

Stellar's Jay,  Photo: National Park Service

Stellar's Jay. Photo: National Park Service

Climate change has California’s birds on the move, but not in the usual direction or at the same pace, a new study has found.  Research suggests that warming temperatures and changing precipitation patterns will cause bird species distributions to shift independently, resulting in new bird “communities” appearing in up to half the state.

In some cases, these new communities will create combinations of birds that have never existed before, a situation that could disrupt the delicate balance of species interactions with potentially unanticipated consequences for whole ecosystems, the report authors concluded.

One of the co-authors, Stanford biologist Terry Root, told Climate Watch: “This will not be just a few species in a few locations–this tearing apart of communities could be quite extensive across California.”

Root was among  researchers from Stanford’s Woods Institute for the Environment, PRBO Conservation Science, the University of California-Santa Cruz, and the Klamath Bird Observatory, who collaborated on the study.  They used bird survey data and climate model projections for California to map current and future bird distributions for 70 species.  Many species often found together, such as acorn woodpeckers and western bluebirds, are projected to shift and adapt in different ways, resulting in these new assemblages.

PBRO has posted interactive maps of the future projections for individual species distributions on its Climate Change, Birds, and Conservation website, in the section called “Where will the birds be?“.

The study authors, including Terry Root of Stanford and Diana Stralberg and John Wiens of PRBO, write that the emergence of new bird communities in the coming decades present enormous conservation and management challenges.  They assert that rapidly changing habitats and ecological communities are going to require new approaches to conservation and management. “As new combinations of species interact, some species will face new competition and/or predation pressures, while others may be released from previous biotic interactions,” they wrote. “Managers and conservationists will be faced with difficult choices about how, where, and on which species to prioritize their efforts and investments.”

Root pointed to experience with wolves, coyotes and foxes, in which wildlife managers tried to control one,  only to see unexpected spikes in the population of another: “Here is a community of only 3 canines to which we purposely forced changes, and we had two big surprises.  Now we are talking about 70 species of birds shifting without any control of the force or the species being changed.  I guarantee there will be a lot of surprises.”