Birds have wings, and they use them—but mostly in predictable ways. Although wild birds seem to have the freedom to wander at will, generally they don’t do it. Northern Cardinals may visit every bird feeder in Illinois, but you won’t see one in Idaho. Bobolinks flutter over meadows all across the northern United States and southern Canada in June, but it would be extraordinary to find even one there in January, when virtually all have retired to wintering grounds in South America. Place and season are among the best predictors of the birds we’re likely to see, and savvy birders always check the range maps in field guides when working on an ID.
However, those range maps are not carved in stone. Distributions of various species change over time. Usually the changes are slow, but they add up.
In North America, for the last several decades, various southern birds have been gradually extending their ranges northward. They include migratory summer birds like Orchard Oriole and Blue-winged Warbler, and year-round residents like Carolina Chickadee and Inca Dove, but they’ve all shifted in the same direction. Meanwhile, hardly any birds have extended their ranges southward. Although the pattern proves nothing by itself, it’s consistent with what we would expect in a warming climate.
So experienced birders were already primed for the basic findings of Audubon’s landmark report on Birds and Climate Change in 2014. That study analyzed the overall set of climate conditions that favored each of 588 species, looked at forecasts for climate change in coming decades, and calculated what would happen to the distributions of those species as a result. For most, ideal climate conditions were shown shifting north or uphill into cooler mountaintops; alarmingly, more than half were predicted to lose substantial parts of their current ranges.
Now, Audubon scientists have teamed up with colleagues from the National Park Service to look at how the accelerating change in climate will affect the birdlife in 274 National Park Service properties. Detailed reports for every park list birds for which the climatic conditions will be getting better or worse or staying the same. The reports also predict some species that might disappear from each park and others that could move in.
The latter category, “potential colonizers,” is likely to raise some eyebrows. Some birds are predicted to move into parks many hundreds of miles away from their current ranges. Some of these range extensions—such as Limpkin and Anhinga (which most birders regard as Florida specialties) on the list for Grand Canyon—seem outlandish at first sight. But are they really that impossible?
Bird species sometimes go through major, rapid expansions of their ranges. Look at the history of the Eurasian Collared-Dove. In December 1974 in Nassau, Bahamas, about 50 of these Old World doves escaped from an aviary. They survived and thrived in the wild, soon spreading to other islands in the Bahamas. No one knows when they first crossed the water to Florida, but they were identified there in 1985. By 1990 they were common over much of southern Florida and were spreading north. Although they still haven’t penetrated much of the Northeast, Eurasian Collared-Doves are now abundant from Florida west to California and from southwestern Canada to southern Mexico, and they are pushing through southeastern Alaska. It took only three decades for them to conquer most of the continent.
Of course, species introduced by humans sometimes do extremely well in new surroundings. Free of the competitors or predators that kept them in check in their native lands, they may spread explosively. House Sparrows and European Starlings, brought to the United States in the 19th century, are now among the most widespread birds in North America. But even native species sometimes go through rapid expansions, for reasons that we may not fully understand.
As recently as 1934, Great-tailed Grackles were found nowhere north of the Mexican border except in southern Texas. But a northward expansion on a broad front brought them to southern Arizona by 1935, Houston by 1938, Oklahoma by 1953, California by 1964, Missouri and Nebraska by 1976, and Iowa by 1983. Their total range has expanded by hundreds of thousands of square miles, and they’re now very common in many places where completely unknown less than 80 years ago.
There are many other examples. The Evening Grosbeak was strictly a western bird until the late 1800s, when it began to expand eastward; by the 1940s it was a common nesting bird in eastern Canada and parts of the northeastern states. Lesser Black-backed Gull was never recorded in North America until a single bird was found in New Jersey in 1934; it was still a very rare visitor in the 1970s but now it’s very common in the eastern states in winter, with daily counts over 500 in some places. As recently as the 1970s, Cave Swallows nested in only a few caves in Texas and New Mexico. Sometime around 1980 they began nesting in culverts and under bridges, and expanded throughout Texas and beyond; now, every fall, flocks of Cave Swallows wander to the central Atlantic Coast and the Great Lakes. White-tailed Kites have quadrupled their range since the 1950s, and Neotropic Cormorants, formerly Texas specialties, are now practically expected as far north as the Great Lakes.
If expert birders from a century ago could come back and revisit their old haunts today, they’d be utterly astonished at how much the local birdlife has changed.
I can hear you saying: Yes, but what about those predictions of Limpkin and Anhinga in the Grand Canyon? Let’s take a look. In Mexico, Limpkins were restricted to the southeastern part of the country as recently as the mid-1990s. Now they’re very common in Nayarit, on the western coast, and surrounding states on the Pacific Coast. Whether they came a thousand miles along the coast, or hundreds of miles over deserts and mountains, they have arrived in force. Another leap like that and they'll be most of the way to the Grand Canyon. As for Anhingas, which are typically found along the Gulf Coast, I’ve seen them along rocky rivers in northwestern Mexico, and there are scattered records from western Texas to southern California. The Grand Canyon doesn’t seem far out of range from that perspective. In the current age of climate change, all kinds of “impossible” bird records are likely to become possible after all.
Does this mean most of the “potential colonizations” listed in the Audubon and National Parks study are likely to become reality? Well, no. A critical point to remember is that this study looked only at the suitability of climate, not other factors like habitat and distance. So, for example, the climate in California’s Redwood National Park is predicted to become suitable for Seaside Sparrows. Will the sparrows show up there? No. Not one chance in a billion. Seaside Sparrows are non-migratory birds of salt marshes on the Atlantic and Gulf Coasts, and they’re not going to cross mountains to colonize a California park. Nor will California Gnatcatchers find their way to the Everglades, even if the climate there becomes perfect for them. Habitat and distance make it simply impossible.
That’s the sobering subtext of this study. Climate change is already underway, and speeding up. It will shake up bird distributions in major ways. In the new study from Audubon and the National Parks Service, species flagged for “potential extirpation” probably will disappear from those parks. Among those noted for “potential colonization,” all of them could move in, in theory, but many won’t be able to make the leap. The presence of the right climate conditions won’t be enough for them to succeed in colonizing.
In this new era, conservationists will have to pay even more attention to all birds across all landscapes, to be alert to what we can do to help species survive. The good news is that we have time. The new study projects these potential range shifts by 2050, which is barely 30 years from now. That’s a timescale we can plan for—and begin acting on. Throughout the country, biologists and conservationists and land managers are strategizing about how to best prepare birds and wildlife for coming changes. Whether it’s ensuring birds have intact “wildlife corridors” through which they migrate north without encountering highways and other human obstacles, elevating coastal land to give marsh birds a chance against sea level rise, or protecting habitat that will be critical for birds in the future, there is plenty of work to be done.
But first, we have to try to imagine changes that might seem impossible today.