Barry Cranmer
The Data

Changing Ranges: Why Bigger Isn’t Always Better

A number of the 314 climate-threatened species could see their ranges expand. Here’s why that’s a problem.

Audubon recently released a scientific study assessing how birds may be affected by climate change in the future. The upshot is not encouraging—314 species could become climate-threatened or climate-endangered, meaning that the climate conditions the birds need to survive will be affected by climate change.

Audubon released maps showing how climate change might affect each species’ range over the next century. If you’ve clicked through some of them, you may have noticed something strange. Many of the 314 species are actually projected to experience range expansions as our world warms—with some expansions as dramatic as ten-fold or more—yet they are still considered threatened by climate change. So what gives?

The simple answer is that while climate is critically important to the survival of a species, it’s far from the only important factor. In addition to the correct climate conditions, the birds still need everything else that creates the appropriate habitat, including the right food sources, proper trees for nesting, and safety from predators. If any element is missing, the bird likely won't survive. 

Here are three species that will experience expanded range, but most likely will not benefit from the space.


Tree Swallow—Nowhere to Nest

This species is already fairly widespread in North America, and climate change will likely cause their climatic range to expand considerably, according to our models.

So what’s the issue? Suitable climate for the species during the summer breeding season is shifting further north, where trees are scarce or nonexistent. This is a major problem for a species that nests in tree cavities.

“No matter what the climate, there can’t be Tree Swallows if there’s nothing to nest in,” said David Winkler, professor and faculty curator of birds at Cornell University.

A warmer climate could allow trees to grow further north as well, but given that forests migrate very slowly it’s unlikely that they would make it there in time.

Visual representation of Audubon's prediction for how the Tree Swallow's range will change.


 Solitary Sandpiper—Too Far to Migrate

Of course, when dealing with birds it’s not just migration of forests that we must keep in mind. Many birds, such as the Solitary Sandpiper, push their physical limits during seasonal migration.

Our climate report predicts that the Solitary Sandpiper will experience a dramatic 1363 percent increase in winter range, most of it northward. Yet Dennis Meritt, an adjunct professor of biological sciences at DePaul University, is concerned about how the species will fare in the face of climate change.

"Let's assume that the projected models are all correct,” he said. “What it means for Solitary Sandpiper is that when it makes annual migration the migratory route is going to be longer."

This could be deadly for birds that are already pushing the limit of how far they can migrate.

“By the time these birds get to their wintering grounds in South America, a lot of them are not going to make it,” said Meritt. “The ones that I've banded have been as beat up and run down as any bird I've handled in in two decades of handling birds."

Visual representation of Audubon's prediction for how the Solitary Sandpiper's range will change.


Mississippi Kite—Human-Spurred Evolution

Even the species that survive climate change may come out of this as changed creatures.

Take the Mississippi Kite, for example, which is predicted to experience an 1819 percent expansion in climatic range. The species naturally inhabits bottomland hardwood swamps, but these opportunistic raptors have actually been getting along quite well in the urban and suburban areas that it has already been pushed into, according to Jim Bednarz, professor of wildlife ecology at Arkansas State University. As climate change progresses, more Mississippi Kites will likely be forced to colonize these drastically human-altered landscapes rather than their regular swamps, Bednarz said.

“I’m concerned that we’re losing the original kite with its original ecology, which is tied to its genetics,” said Bednarz. “We’re basically promoting the evolution of a different form of the Mississippi Kite.”

Visual representation of Audubon's prediction for how the Mississippi Kite's range will change.

At the end of the day, no one knows how species will react to climate change. The projections offered in our climate report are only hypotheses. Climate change is, as Winkler puts it, “a huge experiment without a control.”

Top Image: A flock of Tree Swallows in flight.

Birds at Risk

Explore more birds threatened by climate change around the country.

Allen's Hummingbird
Baird's Sparrow
Bald Eagle
Brown Pelican
Burrowing Owl
Cerulean Warbler
Common Loon
Eastern Whip-poor-will
Golden Eagle
Greater Sage-Grouse
Hooded Oriole
Mississippi Kite
Northern Shoveler
Piping Plover
Ruffed Grouse
Rufous Hummingbird
Spotted Owl
Tundra Swan
White-throated Sparrow
Yellow-billed Magpie

You Can Help

It's easier than you think to make a difference. Become an Audubon member today to help birds facing climate change.

Share Your Pledge

Thank you for pledging to help save the birds most at risk from global warming. But we need everyone’s help–and soon.

Share this urgent message with your friends and family. Tell them why these at-risk birds are so important to you, and ask them to pledge to do their part, too.

When you sign the pledge, you will begin receiving communications from Audubon. You can opt-out of these communications at any time.