Climate change is going to leave a lot of birds looking for new flight patterns. Scientists expect that the migratory ranges of many birds will be profoundly altered as weather patterns shift. The ranges of less adaptable birds will shrink. Species that are more flexible will be able to carve out niches in new areas.
A new report by the Audubon Society modeled habitat suitability for 314 of North America’s at-risk bird species under several different climate scenarios. In each case, the authors balanced the bird’s biology and behavior with predicted changes to the North American landscape. Some birds, like the tree swallow, should fare relatively well (see the illustration below). Others, not so much: Climate change could make the Chesapeake Bay inhospitable for orioles, or Minnesota a bad place for loons. The study’s authors were kind enough to share some of their data so I could explore how climate change might affect some of my favorite species.
One of the things that fascinates me is how different bird species will react once their ranges start to overlap more.
I settled on exploring two iconic species: bald eagles and turkey vultures. Why these two? First, bald eagles are expected to do poorly as the climate warms. Turkey vultures, on the other hand, are predicted to do very well. By reputation, however, each couldn’t be more different. One is the regal, alpha predator that serves as a punctuation mark to patriotic imagery. The other is a carcass-circling scavenger whose name is often used as an epithet for accident lawyers, Wall Street bankers, and people who offer payday loans. Who cares if one invades the others’ range?
As you can see in the top map, the two already share a lot of range, but this is mostly in the southeast. I’m more interested in what’s happening out West. Turkey vultures are the supreme carrion pickers in California’s Central Valley. And, as the the study’s lead author (and Audubon’s chief scientist) Gary Langham points out, turkey vultures are going to do very well as the weather gets warmer. “The turkey vulture could come in to where the bald eagle lives, and start competing for space,” he said.
For those of you who have never been to the Pacific Northwest, where bald eagles gather en masse, the birds act more like alpha scavengers than freedom fighting raptors. (Locals know that dump is usually the best place to go eagle watching, and woe is you if you leave any unattended food in the bed of your truck.) Turkey vultures can hold their own against other carrion eaters in their current west coast range, which takes them to the top of California’s Central Valley. But, I wondered if the warming weather would extend their range and lead to conflict with bald eagles.
The current ranges for the bald eagles and turkey vultures (and every other species in the study) come from observational data collected by volunteers for over 100 years. There are two main surveys—the Breeding Bird Survey for summer, and the Christmas Bird Count for winter. Using these data, the researchers created a database of each species’ preferred habitat. They then used climate data to model how each bird species’ current habitat is likely to contract, hold steady, or expand. “Basically what we did is take a whole bunch of bird observations and marry them to 17 climate variables,” explained Langham.
Here is what the study predicts each bird’s range will be by 2020:
I made my maps using only the winter data because the northward march of winter warmth is one of the strongest factors affecting each species’ range. I also had a choice of which kind of future climate my birds would be dealing with. Predicting the climatic future is tricky business, and the best studies (which come from the Intergovernmental Panel on Climate Change, or IPCC) consider how the planet would look under a number of different emissions scenarios—anywhere from a radical shift to renewables to a “business as usual” fossil-fueled future. For my maps, I asked that Langham give me the data for IPCC’s A2 projection, which assumes that things like energy use and population growth will stay on the similar trajectory to today (in other words, we keep burning oil and making lots of babies).
Their data came to me as shapefiles, a file format that specialized digital mapping platforms called GIS use for spatial analysis and spitting out mathematically precise maps. Because I wanted to make my maps using CartoDB, an online tool that emphasizes map aesthetics over spatial analysis, I had to do a minimal amount of data wrangling before I could get up and running. But once I did things started looking good. Here’s map #3, showing each species extent as of 2050.
At this point, the eagles and vultures are still mostly overlapping in the northernmost part of the Central Valley, but if you look closely, you can see some vulture-friendly pixels opening up southern Oregon’s Siskyou mountains. Let the roadkill wars begin!
In the final map, of 2080, you can see that bald eagle blue, which dominated the Northwest region in 2050, has started to dissolve to white. Meanwhile, turkey vulture red is becoming less of a sprinkle and more of a smear. The map indicates that the’ve found a solid winter foothold in Oregon, all the way up to the Washington border.
Everything about climate change is complicated. As warmer weather moves a bird’s range into new ecosystems, they’ll encounter new mixtures of plants, animals, topography, humans (and their associated attitudes towards birds), and other birds. These maps show how two species at odds with one another for resources might come into contact. But, it doesn’t show how, or if, that conflict will actually play out. The data only reflect habitat suitability. So, while the maps appear to show the turkey vultures pushing eagles northward, this is coincidental with the type of habitat that is suitable for each.
In competitions between birds, size typically trumps other factors. While it’s possible that turkey vultures could reach a critical mass and start chewing resources (RE: dead things) before eagles can get to them, it’s unlikely that a kettle of vultures could keep a mating pair of eagles from taking possession of a carcass. (Bald eagles can be jerks. I once saw one bully an osprey into giving up its freshly-caught salmon while in mid-flight). “Turkey vultures are not going to be muscling out the bald eagle, they are just going to be competing for the space,” said Langham.
These maps give scientists like Langham, and advocates like Audubon, a look at the landscape of climate change so they can adapt their conservation strategies accordingly. And they invite you to do the same. If you are interested in looking at Audubon’s data, you can check out their website, or send a request to climatescience*@audubon.org* and start making maps of your own.
Thanks to Raf Verbraeken, who designed the eagle icon, and Yi Chen who designed the vulture. I found both icons at Noun Project.
