Texas gold

On a recent trip to Texas, I visited two refuges in hopes of getting glimpses of two of the rarest birds in the United States: the Golden-cheeked Warbler and Black-capped Vireo. Both winter in Central America and return every spring to nest in extremely specialized habitats.

The warbler nests nowhere on the planet but the oak-juniper canyons of central Texas. Partners in Flight estimates the warbler population is 21,000, and a group of scientists led by the Smithsonian National Zoo places the population at about 34,000. The Black-capped Vireo (total population: 8,000) breeds in a narrow band of scrubby brushland extending from Mexico through central Texas and into Oklahoma. Neither bird was ever numerous, and urbanization and fragmentation of their habitat have ensured them a spot on the Endangered Species List.

My first stop was Canyon of the Eagles Nature Park, on the shores of Lake Buchanan, 70 miles northwest of Austin, where Melanie Pavlas, environmental coordinator for the park, was my guide.

Going for the gold

We hear a scratchy zee-zee-zee song in the distance and hurry up the wooded slope. The trail leads out of a narrow canyon onto a dry ridge studded with prickly pear cacti and yucca. From here, we can see over the treetops to the opposite slope. Melanie spots movement in a nearby live oak, and we all freeze. Two birds flit in and out of the leaves, then one hops onto an exposed branch. The side of its face blazes yellow in the sun. The bird throws back its head and belts out a buzzy, repetitious call. “It’s a pair of Golden-cheeked Warblers,” Melanie whispers. The energetic birds forage for five minutes before zipping off to another tree.

“Golden-cheeked Warblers like wooded canyons with a mix of deciduous trees and mature juniper or cedar,” she says as we listen to the warblers calling from across the canyon. “The cedar has to be 20 to 40 years old to have the long, stringy bark the birds need to build their nests. The Black-capped Vireo lives in the opposite habitat. It likes early successional, brushy growth, the kind you find around the edges of clearings or after fires. Decades of cedar eradication and wildfire suppression by ranchers destroyed both birds’ habitat. Now, urban sprawl is the main threat.”

The trail follows the ridge, then drops back into the dense canopy of hardwoods and junipers. “This is perfect Golden-cheeked habitat,” Melanie tells us. “The warblers prefer steep slopes and complete canopy cover. Less than a 50 percent cover produces only marginal habitat for the birds.”

Privileged views

Each spring, the Golden-cheeks leave their winter home in pine-oak highlands that extend from Chiapas, Mexico, through Guatemala, Honduras, and Nicaragua. The males arrive in Texas in early March and establish three- to six-acre territories. They crisscross their domain and proclaim ownership from treetop perches. “Golden-cheeks are active feeders and singers. They’re not difficult to see in the right habitat,” Melanie says.

The females arrive a few weeks later and by early April have laid three to five eggs in a tightly woven cup nest. The warblers conceal the nest about 15 feet high in a tree fork. Few people, even biologists who study the birds annually, ever discover a nest. I searched a small sanctuary near my home for three years without success. About 12 pairs nest in the Canyon of the Eagles Nature Park.

The eggs hatch in 12 days, typical for small songbirds. “During nesting, the parents glean caterpillars and spiders from the deciduous trees for the hatchlings,” Melanie says. The mix of hardwoods and deciduous trees ensures an abundant variety of food throughout the nesting season.

We stop under a huge native pecan tree by a seeping spring and wait for birds to come to drink. A flamboyant Painted Bunting lands in a tree, and we snap our binoculars to our eyes. With a blue head, red belly, and green back, the bunting looks as if it had been painted by a kindergarten class. We see Orchard Orioles, a Lazuli Bunting, White-eyed Vireos, Black-crested Titmice, Greater Roadrunners, and Blue-gray Gnatcatchers.

Besides the two endangered songbirds during spring and summer, a Zone-tailed Hawk regularly nests on the lake, shorebirds stop over during migration, and Bald Eagles winter there. The park offers exciting birding nearly year round. But during warbler and vireo nesting season, from March through August, visitors may enter the birds’ protected areas only in the company of a park ranger.

Some like it hot

After lunch in the park lodge, we join Melanie for an afternoon birdwalk in the shrubland savanna that extends from Lake Buchanan to the hilly escarpment. Now our quarry is the Black-capped Vireo. “Black-capped Vireos like it hot and feed all afternoon,” she tells us as we enter a gated section of the preserve. “We have about 20 nesting territories in this section.”

A 12-foot-high, deer-proof fence surrounds the area in order to prevent deer from overgrazing the undergrowth. “We manage for habitat, not individual species,” Melanie says. “With the right brush control, deer management, and periodic burns, we attract the vireos and warblers. Black-capped Vireos like early successional habitat, [which is] easy to re-create with controlled burns and clearing. The old-growth junipers for the Golden-cheeks take decades to develop.”

For Black-capped Vireos, structure is as important as the species mix of trees. The denser the undergrowth the better. The vegetation makes spotting the elusive birds a birdwatcher’s torment. We walk silently along a trail bordered with an impenetrable thicket of persimmon, mesquite, prickly pear, and beebush. Waist-high Mexican hat wildflowers cover the little-used path and pollinate our pants with mustard-colored splotches.

Along the trail, we pass an empty Brown-headed Cowbird trap. “We’re not trapping right now,” Melanie says. “We don’t have many cowbirds this year.” During most years, the walk-in cages are a vital part of the endangered vireo and warbler recovery programs at all the refuges and parks throughout the vireo breeding range. Nest parasitism (from the cowbird), combined with habitat loss, remain the major ongoing threats to both birds.

The fussy calls of Blue-gray Gnatcatchers and Bewick’s Wrens follow us along the trail. We stop and work on a White-eyed Vireo singing in a hackberry tree. Earlier, I found a Bell’s Vireo nest with eggs along the lakeshore. This is vireo paradise. Finally, Melanie hears a Black-capped Vireo’s jumbled call notes deep in the thicket. We gather around with our binoculars and search the tangled vegetation for signs of movement. The twittering moves erratically through the foliage.

Black-caps have a huge repertoire with dozens of screechy squeaks. Unfortunately, this vireo isn’t inclined to give a command performance. It keeps foraging within earshot but refuses to pop into view. Since the birds are endangered, we can’t entice him into view with a recording or even a psssh. During the three-hour walk, we hear the birds’ wheezy chatter at several other locations but never get a glimpse.

Hitting the jackpot

We’ll have a second chance at the bird a few miles down the road at the Balcones Canyonlands National Wildlife Refuge — the best place to see the elusive vireos. “We have what we call the ‘world famous’ Shin Oak Observation Deck,” Chuck Sexton, the refuge biologist, tells me with a laugh. “You can almost always see Black-capped Vireos from the platform. Typically, three to five pairs establish territories within earshot and viewing distance of the deck. They sing almost continuously during the nesting season.”

The observation deck is open daily except for the first two to three weeks of April, when the vireos are establishing nesting territories. No trails lead from the deck, but the Warbler Vista Trail and roads in other parts of the refuge provide access to both Black-capped Vireo and Golden-cheeked Warbler habitats.

“We found that carefully controlled field trips don’t disturb the nesting birds,” Chuck says. “The vireos adjusted quickly to the deck and the level of visitation. They feed their young without paying any attention to the birdwatchers. To them, the deck is just another landscape object.”

The vireos build their nests in a two- to five-acre territory. “We have about 100 nesting territories on federally owned land,” Chuck says. “The population is increasing gradually as “we establish new habitat by prescribed burning. We cut out shrubby cedar and burned a ridgetop. Shin oaks grew waist-high in two years, and two pairs of Black-capped Vireos moved in to nest. In areas with the right species structure, we can create vireo habitat in 3 to 5 years that will last for 20 years.”

Black-capped Vireos build hanging nests on a branch tip three to four feet off the ground, where they are particularly susceptible to predation by small animals. Snakes, raccoons, skunks, and feral cats destroy many nests. By mid-September, the birds leave for the thornbrush of southwest coastal Mexico, where they spend the winter.

At the end of June, vireo watchers got a special treat at the observation deck. A pair of Black-caps built a nest 1.5 feet from the platform. The male sang in the trees, and the birds incubated four eggs in easy view. Three eggs hatched. “We had 20 people at a time watching the nest without disturbing the pair. It was an amazing event to see so close,” Chuck says. “Unfortunately, on July 3, a snake predated the nest, and we lost all three chicks.”

Black-capped Vireos once nested from northern Mexico through central Texas and Oklahoma into Kansas. They disappeared from Kansas in the 1950s and remain gravely endangered in Oklahoma. In 1986, only 32 pairs nested in the Wichita Mountains Wildlife Refuge; then wildfires swept through and opened up new habitat for the vireos. In 2002, the refuge surveyed 635 nesting pairs. Fort Hood, 40 miles north of Lake Buchanan, also harbors substantial populations of both Black-capped Vireos and Golden-cheeked Warblers.

The Golden-cheeked Warbler can also be seen at Balcones Canyonlands NWR, which supports about a thousand pairs of the bird. The Warbler Vista Trail and other trails, which vary from easy strolls to vigorous ridgetop hikes, lead through prime warbler habitat. “We have a stable, growing population of Golden-cheeks,” Chuck says. “Some of our transitional sites are maturing into prime habitat with 12 to 20 pairs per 100 acres.”

Each spring on the first weekend in May, Balcones Canyonlands and the nearby town of Lago Vista sponsor the Texas Songbird Festival to showcase the two endangered birds. “We had a great festival this year with a full slate of field trips,” Chuck says of the 2004 event. “The observation deck came through gloriously with great views of the vireos.”

With limited distribution and low populations, Golden-cheeked Warblers and Black-capped Vireos require an extra effort and a little luck to see. Fortunately, at Canyon of the Eagles Nature Park and Balcones Canyonlands, you can be at the right place at the right time for both birds.

George Oxford Miller is a naturalist and photographer and the author of eight books, including Landscaping with Native Plants of Texas (Voyageur Press, 2013), Texas Parks and Campgrounds (3rd ed., Lone Star, 2009), and A Field Guide to Wildflowers, Trees, and Shrubs of Texas (Lone Star, 2003).

 

Originally Published June 1, 2005