Texas Parks & Wildlife Magazine   


The Big Shift

Why are birds, butterflies and other wildlife showing up where they've never been before?

By Rusty Middleton

"Oh, oh, I think I heard an Audubon's oriole!" said Selma Glasscock as she turned around excitedly and stared hard into the South Texas brush, her binoculars still dangling from her neck. Even in December the brush here is a thick, chaotic mass of mesquite, cedar elm, oaks, vines and elbow-bush. "In this country you 'spot' birds as much by sound as sight," she said, giving up the search for the moment.

For many birders, the sight of an Audubon's oriole would be a special thrill, because not so long ago you would have needed to go all the way to the Lower Rio Grande Valley to see one. Now there are reports of Audubon's sightings near Beeville and here in the vicinity of Welder Wildlife Foundation, 150 miles north of the Valley. And the Audubon's oriole has lots of company.

Around the Welder Wildlife Foundation's 7,800-acre wildlife refuge near Sinton (just north of Corpus Christi), dozens of new species are showing up from the south. Striking, and very tropical looking, green jays flit around the refuge headquarters, calling raucously at each other. Once confined to the Valley, they now are seen near Pleasanton, Cuero and as far north and east as Lake Jackson. Great kiskadees once were seen only in the extreme southern tip of Texas. Now there are several pairs of them just west of Houston.

"When we saw the first kiskadee here at Welder we didn't know what it was," said Glasscock, assistant director of the refuge. "We were excited. It was jaw-dropping."

More than 70 species of South Texas birds have moved north and east, according to John Rappole, formerly of Texas A&I University (now Texas A&M-Kingsville) and a senior research scientist with the Smithsonian National Zoological Park. In a recently released book, The Changing Climate of South Texas 1900-2100, Rappole just goes ahead and says it. The best explanation for birds moving north and east is climate change.

Other scientists aren't quite there yet. It's not that they don't believe that global warming is happening. It's just that making assertions about climate change for specific species in Texas, where the effects of global warming are not as obvious, still makes them a little uncomfortable.

"Scientists are conservative," says Glasscock, who holds a doctorate in systems ecology. She is friends with Rappole and helped him conduct his recent research on the changing ranges of Texas birds at Welder Wildlife Foundation. She's a little wary of the "bandwagon effect" in ascribing range changes to global warming when there are so many factors possibly at work. "There are so many things that can affect bird behavior. There are grazing, fencing, fire suppression and invasive species. Agriculture is a big one, as well as human construction, among others. It's a long list. Plus, as we all know, the weather oscillates. We may just be in a warm phase now."

A recent analysis of weather patterns by scientists at Texas A&M-Kingsville reveals that the climate in South Texas has been warming steadily for about the last 30 years, just as it has elsewhere. In fact the '90s was the warmest decade on record, and 1998 was the warmest year on record. Before that, the South Texas climate had not shown much variation from its known historical patterns.

Tim Brush, an ornithologist with the University of Texas-Pan American in McAllen who has studied Valley birds since 1991, agrees that the climate change explanation for all the new birds he sees may be going a little too far out on a limb for him.

"I'd rather be closer to the tree," he laughs.

Brush cites the massive conversion of bird habitat in Mexico over to farmland as a possible reason why so many Mexican species are showing up in the Valley area in recent years. Brush is seeing short-tailed hawks, tropical kingbirds and clay-colored robins among many new southern species. (Altogether, a remarkable 513 species of birds have been sighted in the Rio Grande Valley.) Brush also thinks it is important to remember that one of the most fundamental behaviors of any species is to increase its population and expand its range. Fluctuations in population and range are a normal and constant part of evolution.

Rappole does not ignore the many possible causes. In fact, he has studied them extensively and found that for some species there are reasonable non-climate-related reasons for change. For example, the large influx of white-winged doves from the south, especially into urban areas, might be explained by the "heat island" effect of cities and the large number of people who are feeding birds in their backyards. And the appearance of cave swallows in Texas could credibly be attributed to the availability of many structures like highway bridges that provide new nesting opportunities. But for most birds, there was no particular explanation, Rappole found. Indeed habitat is declining for many species due to urbanization and expanding agriculture. Yet the birds are here and they keep coming.

Rappole's conclusion: The only explanation that holds up, when you look at the total number of range expansions as a whole, is a changing climate. And Rappole is not alone. Other ornithologists, such as John Arvin at the Gulf Coast Bird Observatory in Lake Jackson, agree that the best explanation has to be climate change.

And when you look at an even bigger picture, encompassing other plants and animals in Texas, that conclusion seems stronger still.

Marine Life

Mark Fisher, science director at the TPWD Marine Laboratory in Rockport, says new species of fish are showing up in the northern Gulf of Mexico.

"Gray snapper have definitely been moving north since the 1990s," said Fisher. Once found only in the lower Laguna Madre and off the shore of the extreme southern tip of Texas, they are now migrating all the way up to the Galveston area. Their growth has been "exponential," said Fisher. Plus, snook have been appearing more frequently in Texas waters, although not in large numbers. Even the permit, a fish once known only in the tropics, is showing up in Texas when the water is warm enough.


Then there are the butterflies. Although butterfly specialists caution that some new records could be attributable to the fact that more people are interested in, and thus looking for, butterflies these days, there are an awful lot of new sightings of southern species. Josh Rose, a TPWD natural resource specialist at the World Birding Center in Bentsen-Rio Grande Valley State Park, was thrilled to see the one-spotted prepona on a baited post just outside the park's visitor center in early December 2007. (His butterfly bait is an unpleasant looking but effective combination of mashed-up old bananas combined with some brown sugar and a few other ingredients.) This was only the second sighting in the U.S. of this species. The recent appearance of rare Mexican butterflies such as the Guatemalan leafwing and telea hairstreak in other areas of the Valley made news around the country.

But the appearance of new species is not just happening in the extreme south of the state. Butterflies once confined mostly to Mexico are showing up all over South and Central Texas. A variegated skipper appeared in Kerr County, and malachites have been seen across much of the southern half of Texas during 2007. Uncommon species such as blue-eyed sailor, red rim and common mestra have been seen around Austin.

More famously, Camille Parmesan, associate professor of biology at the University of Texas at Austin and member of the Intergovernmental Panel on Climate Change, testified before Congress: "We're seeing many tropical species moving into the Gulf Coast states - former migrants like the rufous hummingbird and the green jay have become year-round residents in Alabama and Texas, respectively. Florida has five new species of tropical dragonfly. Many tropical butterflies that are normally confined to Mexico are starting to breed as far north as Austin, Texas."


The United States Department of Agriculture map of plant hardiness zones has shifted north for most areas of the country by one or two zones since 1990. Biologists agree that studies of changes in wildlife cannot be separated from changes in the plant communities they depend on, either directly or indirectly. There are signs of temperature-related changes in plant communities in Texas, also.

Early maps of the Texas coast showed only about 65 acres of black mangrove habitat in the Mission-Aransas Bay areas just north of Port Aransas. Nowadays, there are at least 15,000 acres of black mangrove in that area alone. This has happened mostly within the last 20 years, according to Paul A. Montagna, a marine science professor at Texas A&M-Corpus Christi.

All mangrove varieties are intolerant of freezing temperatures, and red mangrove is even more sensitive than the black variety. Coastal scientists say that it is red mangrove that may show the most dramatic response to rising temperatures in the future. In fact, it already has. Since 2005, red mangrove has become established in several areas along the Texas coastline, from South Padre Island to Matagorda Island along the central coast. This plant had been restricted to Mexico and the extreme southern tip of Florida in the past. Scientists see red mangrove as very much an indicator species for climate change along the Texas coast.

There have been some changes observed inland as well. Lynn Drawe, executive director of the Welder Wildlife Foundation, has tracked habitat at his refuge for decades. Although he is not ready to attribute the changes to global warming (simply because he doesn't know the cause), he has seen exponential growth in elbow-bush and a near doubling of overall brush cover since the refuge was first surveyed in 1939. "It has just amazed me how elbow-bush has gone from just scattered small plants to huge and pervasive," he said. Other scientists in South Texas have also noted that brush is noticeably thicker than it used to be in past decades.

Predictions for the future

The first paragraph of the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report begins with the statement: "Warming of the climate system is unequivocal, as is evident from observations of increases in global average air temperature and ocean temperature, widespread melting of snow and ice and rising global average sea level."

Such a worldwide consensus of hundreds of scientists indicates that there is no longer any meaningful debate over the reality of global warming. It is already happening. Although the effects are manifesting more dramatically at the poles, Texas is already being affected and will be even more in the future. The questions now are how much will we be affected and when.

Although no one really knows the exact answers, Texas scientists have been able to make fairly detailed predictions based on recent global and local climate studies. Jim Norwine, regents professor of geography at Texas A&M-Kingsville, has written extensively about climate in Texas. In talking about the future, he says, "Think about Corpus Christi moving, climatically, about 100 miles south and west." It will be dryer, not because the rainfall is expected to decrease, but because it will be hotter, by about 7 degrees Fahrenheit by 2100, based on current assumptions. Water will become increasingly scarce.

"Frankly I still have a little trouble getting my mind around a 7-degree increase within about 100 years," Norwine says. "I mean, we've only had a 9-degree increase in the last 10,000 years. It kind of blows your mind."

Dry spells will last longer, rain events will be more intense and the entire climate regime will likely shift east, with western South Texas becoming semi-desert and eastern South Texas becoming semi-arid, he says. Although Norwine's studies are specific to South Texas, he says they can be extrapolated to the rest of the state. Commensurate changes in wildlife can be expected.

Texas scientists have also made forecasts for the Texas coast. Paul A. Montagna and John W. Tunnell Jr., of Texas A&M-Corpus Christi, and James C. Gibeaut of UT-Austin say a rising sea level will bring major changes to the coast. While they are less sure of the magnitude of the changes due to uncertainty about how much humans will intervene in global warming, they are more confident about the trends.

Increasing sea level will result in more frequent and longer flooding of marshes that could eventually convert to open water. Seagrass beds will appear and disappear with changing water depths. Tidal flats will spread inland, and bays and estuaries will grow. Erosion could cause steeper shorelines that would change the habitat for mangrove, tidal flats and marshes. Ranges of marine species would certainly change.

Other scientists predict that if the sea level rises high enough, the barrier islands will disappear, eliminating the protection they provide from increasingly active storms.

Norwine cautions that most predictions about sea level rise are based on business-as-usual assumptions, meaning no reduction in greenhouse gas emissions. With no reductions, sea level is expected to rise by 7 to 10 feet by the end of the century.

James Hansen, the NASA scientist who first sounded the alarm about global warming, says that if there is a rapid disintegration of the Greenland and Antarctic ice sheets, the rise could be as much as 20 feet by 2100.

Two things are certain about wildlife and plants in Texas. Changes have already happened, and more are on the way.


The Changing Climate of South Texas 1900 - 2100 is available from the Texas A&M-Kingsville bookstore or by contacting Jim Norwine at kfjrn00@tamu.edu.

back to top ^

Texas Parks & Wildlife Magazine 
Sign up for email updates
Sign up for email updates