One Ecosystem - Two Countries: Conserving the flora and fauna of the Lower Rio Grande Valley

One Ecosystem - Two Countries: Conserving the flora and fauna of the Lower Rio Grande Valley

Article by Robert Fears
Photos by Larry Ditto, Ben Masters, Katy Baldock, Steve Bentsen, Wyman Meinzer, Steve Nelle


Halfway between Dallas and Mexico City lies the Lower Rio Grande Valley which spans across the southern tip of Texas and the northeast corner of Mexico. Including both countries, the Rio Grande Valley has a population of more than 2 million people. The population swells during the winter, as the valley’s warm climate brings many retirees from the northern states to the Texas side of the river for seasonal habitation.

“About 250 years ago, the valley’s climate and lush vegetation provided habitat for a wide array of wildlife, including some species which were not seen in other areas of the state,” said Dr. Wayne Hanselka, Professor and Range Science Extension Specialist Emeritus, Texas AgriLife Extension. “Today, agriculture is dominant in the valley on both sides of the river with production of sorghum, citrus, sugar cane, potatoes, nursery plants, cotton, spinach and other heat tolerant vegetables.

“Agriculture and urbanization have replaced a large majority of the natural habitat leaving only a few areas resembling their pre-settlement condition. These protected areas of native flora and fauna are mostly in state parks or federal wildlife refuges.”

Geographical Location and Environment

The Rio Grande Valley constitutes the Matamoran District of the Tamaulipan Biotic Province. William Blair, Ph.D., described the seven biotic provinces of Texas in an article published in Texas Journal of Science in 1950. None of the seven provinces are completely limited to the state but extend over its borders into other areas.

The Tamaulipan province includes most of South Texas from San Antonio through the northeastern corner of Mexico to Tampico in the state of Tamaulipas. Biotic providence is defined by the McGraw-Hill Dictionary of Scientific and Technical Terms as a community occupying an area where similarity of climate, physical geography and soils leads to recurrence of similar combinations of organisms.

Blair divided the Tamaulipan Biotic Province into two districts: Nuecian and Matamoran. The Matamoran District encompasses Starr, Hidalgo, Willacy and Cameron counties in Texas and the northern half of Tamulipas in Mexico.

Although the Matamoran District is referred to as Rio Grande Valley, it is not an actual valley. The region is a delta or floodplain containing many oxbow lakes (resacas) formed from meanders in the river’s earlier courses. Most of the valley is fairly flat with an average elevational rise of about 5 feet per mile.

“The Rio Grande Valley’s climate varies between subtropical and semiarid with long, hot summers and short, generally mild winters,” said Dr. Timothy Brush, University of Texas Rio Grande Valley. “Prevailing winds from the Gulf of Mexico keep the district cloudier and more humid than areas farther inland. These winds keep daytime temperatures lower and nighttime temperature higher than in more inland areas.”

According to Brush, the area’s rainfall is notably erratic and unpredictable. The amount of rainfall is higher close to the coast with an annual average of 27 inches at Brownsville compared to 20 inches at Falcon Dam.

In the summer (May – September), daily temperature highs average from 90 to 95 degrees Fahrenheit while at Falcon Dam and Rio Grande City daily highs of 95 to 100 degrees are common. Daily temperatures vary the least on the beach with overnight lows in the low 80s and daytime highs in the upper 80s. Overcast skies in winter, which usually follow strong cold fronts, reduce chances of frosts.

The Texas Almanac describes soils in the Rio Grande Valley as mostly deep, grayish-brown, neutral to alkaline loams in the upland areas. In the coastal areas, they are mostly gray, silty clay loam and silty clay. Some of the coastal soils are saline. The lower Rio Grande Valley comprises about 2.1 million acres; a large majority of the farmland is irrigated.

“Plant species in the valley are numerous, varied and adapted to a semiarid climate with undependable moisture,” Bush said. “For instance, due to less rainfall, Mexican olive and fiddlewood are usually shrubs in the Valley while tropical relatives are trees.

“Conversely, honey mesquite is a small to medium sized tree in Valley riparian habitats, but in the adjoining drier areas of Texas and northern Mexico, it only reaches shrub stature. Black mangrove is the single tree in the Valley’s coastal salt flats; however, it only reaches 3 feet in height. Cedar elm, black willow, sugar hackberry, Mexican ash and the rare Montezuma bald cypress may reach a height of 65 feet in moist bottomland soils. Sabal palm, Texas ebony, anacua, tepehuaje (lead tree) and western soapberry may reach a height of 50 feet, while mesquite, colima and brasil normally have a maximum height of 30 feet.”

In the lower Rio Grande Valley of Texas, there are 1,200 different plants, 300 butterflies, at least 520 birds and approximately 180 other vertebrates. Two of the best places to view protected areas of native flora and fauna on the Texas side of the river are the Laguna Atascosa and Lower Rio Grande Valley Wildlife Refuges.

Texas is fortunate that the wildlife refuges, state parks, concerned citizen groups and private landowners on both sides of the Rio Grande River are working hard to conserve natural wildlife habitats in the subtropical valley.

Laguna Atascosa National Wildlife Refuge

The largest wildlife refuge is Laguna Atascosa National Wildlife Refuge with more than 97,000 acres and is composed of three units: Bahia Grande, South Padre Island and Gulf Coast Restoration. There are numerous animal species in the refuge, including ocelots, Aplomado Falcons, Kemp’s Ridley sea turtles and Redhead Ducks.


Ocelots are of great concern because fewer than 80 of these endangered wild cats are found in the United States with all of them residing in South Texas. They are often confused with bobcats, but ocelots are smaller and have longer tails. Adults stand about a foot high, weigh 15 to 30 pounds and are about 3 feet long from their nose to the tip of their tail. Ocelots have a long ringed tail and black rounded ears with a large white spot.

Brush clearing is the biggest threat to ocelots because they need a lot of space. Male ocelots typically have a territory of about 25 square miles while the females’ territory is approximately 9 square miles. Their diets consist of mostly rabbits, mice, rats and birds. The ocelot’s food supply is housed by brush species such as Texas ebony, granjeno and colima.

Kemp’s Ridley Sea Turtles

Kemp’s Ridley sea turtles lay eggs on the Gulf Coast beaches of South Padre Island. Their range includes the Gulf coasts of Mexico and the United States as well as the Atlantic Coast of North America as far north as Novia Scotia and Newfoundland. Nesting, however,
is limited to the western Gulf of Mexico, mostly in Tamaulipas and Vera Cruz, Mexico and regularly in Texas. Decline of this species occurred primarily because of activity including direct harvest of adults and eggs and incidental capture in commercial fishing nets.

One of the smallest sea turtles, the Kemp’s Ridley is about 2 feet in length with a maximum weight of approximately 100 pounds. The top of its shell is oval shaped, being as wide as it is long. Its shell is usually olive gray in color. The turtle’s diet primarily consists of crabs, fish, jellyfish and mollusks.

Northern Aplomado Falcon

The Northern Aplomado Falcon is an endangered species found in South Texas and the Trans-Pecos region. Its total geographical range extends to the tip of South America. The falcon’s habitat is open grassland or savannahs with scattered trees or shrubs.

There are many theories on its population decline; however, in South Texas, it is probably due to encroachment of mesquite into their habitats. Aplomados are sensitive to human disturbance, especially during breeding season. They are recognized by a steel grey back, red breast and black sash on their bellies. Another striking characteristic is black marking on the top their heads and around the eyes extending down their faces.

Northern Readhead Duck

An estimated 80 percent of the North American Redhead Duck population winters in the Laguna Madre of Texas and Mexico. The ducks breed in northern prairies of the United States and Canada and intermountain marshes of the west.

A significant migration corridor extends from southwestern Manitoba and southeastern Idaho to the Gulf Coast. Their preferred habitat is non-forested environments with deep water areas. Redheads dive to feed on seeds, rhizomes, tubers of pondweeds, wild celery, water lilies, aquatic grasses, small fish, mollusks and aquatic insects.

Males have the distinct reddish heads and upper necks whereas the females have reddish-brown heads, necks and breasts. Redhead ducks are on the watch list and their populations have remained relatively steady since 1955 at about 400,000 to 800,000 birds. It is thought that their previous decline was due to over-hunting since the colorful bird is a favorite.

Lower Rio Grande Valley National Wildlife Refuge

The Lower Rio Grande Valley National Wildlife Refuge is smaller than the Laguna Atascosa National Wildlife Refuge with approximately 91,000 acres. Like the Laguna Atascosa National Wildlife Refuge, this refuge has several distinct biotic communities that protect numerous plant and animal species.

The Ramaderos biotic community sits on the refuge’s western edge and its landscape is cut by deep arroyos and small tributaries that extend for miles from the Rio Grande River. The definition of ramaderos is: “valleys that cut through bluffs.” These humid corridors of lush riparian vegetation provide unimpeded travel lanes for wildlife.


Peregrine Falcon

At the refuge’s eastern edge of the refuge is the clay loma/wind tidal flats biotic community that is interspersed with saline flats, marshes, shallow bays and unique dunes of wind-blown clay known as lomas. Following the last few miles of the Rio Grande River, this tract links coastal and river corridors and is staging ground for the endangered Peregrine Falcon. Staging ground is where birds assemble in large flocks for migration. This biotic community also provides habitat for 17 other threatened and endangered species, including Kemp’s Ridley sea turtle and ocelot.

Houston Audubon describes the Peregrine Falcon as a large raptor with bluish-gray body feathers and a dark face that varies from a single stripe to a full hood. Falcons are distinguished from other raptors by their sharp pointed wings and faster and more frequent wing flaps during flight. Peregrine Falcons mostly hunt by diving for small birds found in open areas, particularly beaches. Ornithologists at Cornell University report that Peregrine Falcons fly to heights over 3,000 feet, then close their wings and dive down toward their prey. Their dive speeds may reach 200 miles per hour. In traveling flight, the falcon’s speed averages 25 to 34 miles per hour, but it reaches speeds of 69 miles per hour in direct pursuit of prey.

Plain Chachalacas and Green Jays

Resacas and dense bottomland forest are characteristics of the mid-valley riparian woodlands biotic community in the Lower Rio Grande Wildlife Refuge. This habitat is particularly inviting to birds such as Plain Chachalacas and Green Jays as well the endangered and elusive jaguarundi and the rare Bailey’s ball moss. The brush-bordered resaca attract many of the neotropical migrants and waterfowl that funnel through the Valley on their way to and from Central and
South America.

“Plain Chachalacas are an impressive Valley specialty that resemble a Pheasant in appearance, but act like a cross behind a Roadrunner and a monkey,” Brush said. “Chachalacas easily climb from branch to branch eating leaves, fruits and buds. The birds make a lot of noise as they jump from branch to branch and push through the foliage.”

According to Bush, the loud chorusing Chachalaca song that sounds like the bird’s name can be heard hundreds of yards away and underscores the Valley’s tropical feel.

“When one pair or group starts singing, others pick up the beat until the woods resound with the Chachalaca chant,” Bush said.

Plain chachalacas are well represented in fossil records and may have survived from the age of dinosaurs. Chachalacas do not fly for very long. The white muscle fibers in their chest are good for short bursts of speed to escape predators, but the birds quickly tire. In contrast, running and climbing do not tire chachalacas easily.

“Habitat for Green Jays are primarily thorny scrub and tall riparian forest, especially where there is understory,” Brush said. “In the Valley, Green Jays make nests of thorny twigs which are interlocked for strength. They are inquisitive birds, alert to any changes in their environment. They are often the first to respond to predators with intensification of their normal eh-eh-eh-eh calls.”


Texas Parks and Wildlife Department biologists describe jaguarundis as slightly larger than a domestic cat, weighing eight to 16 pounds. They are a solid color, either rusty-brown or charcoal gray.

Jaguarundis move in a quick weasel-like manner and can climb trees and spring into the air to catch prey. They are good swimmers and enter water freely. Jaguarundis are active mainly at night which makes them hard to detect. Like ocelots, they are found in dense, thorny shrubland.

Bailey’s Ball Moss

Bailey’s ball moss is an endophyte which is also known as reflexed air plant. An endophyte is a plant that lives inside another plant. Preferred hosts of Bailey’s ball moss include live oak and Texas ebony. The plant is found along the Gulf Coast from Corpus Christi to Tampico.

Speckled Racer Snake and Southern Yellow Bat

On the edge of the riparian woods in the Lower Rio Grande Valley Wildlife Refuge is a unique and severely diminished biotic community of sabal palms. The palm grove of about 50 acres is a stronghold for the rare speckled racer snake and the southern yellow bat. In addition, more than 900 species of beetles are found in the grove, which aid in plant pollination and other essential ecological functions.

The speckled racer snake, a fast-moving non-venomous snake, is recognized by its dorsal scales that are black-edged with a yellow dot in the centers and a blue base creating an overall greenish hue. The reptile’s undersides vary between white, yellow and green. Adults reach lengths of 30 to 40 inches. If captured or cornered, it is apt to bite.

Southern yellow bat is a subtropical, generally solitary species which roosts year-round beneath hanging dead fronds of palm trees. It is a medium-sized bat with dull, sooty yellow fur. It is presumed to eat small- to medium-sized insects.

Additional Flora and Fauna in the LRGV Wildlife Refuge

The woodlands potholes and basins biotic community on the refuge contains numerous freshwater playa lakes and three super-saline lakes. Black-necked Stilts, Black Skimmers, Least Terns and Gull-billed Terns are found nesting along shorelines of the salt lakes. The salty waters support brine shrimp and a few species of salt-tolerant water insects.

Freshwater potholes and playa lakes in low woodlands of honey mesquite, prickly pear and lote bush serves as favorite roosting and feeding areas for migrating geese, waterfowl, shorebirds and Sandhill Cranes.

The Valley Land Fund

Since 1987, the Valley Land Fund has worked in partnerships with public organizations, private individuals and groups in facilitating the protection of more than 11,000 acres of wildlife habitat through gift, purchase or conservation easement. The Valley Land Fund assists with conservation of native habitat by protecting land in the Lower Rio Grande Valley. It is committed to educating the public about the importance of conserving land and protecting our natural resources.

The Valley Land Fund uses a number of tools for outreach and education; the most popular is its annual wildlife photo contests. Using photography to educate the area’s citizens is one of the most important aspects of our approach to wildlife conservation. By using award-winning images, we are able to make individuals, young and old, aware of our wonderful natural heritage including every species of plant and animal that is in jeopardy.

Private landowners play a crucial role in wildlife conservation. Without their participation in conservation, entire ecosystems will be lost. The Valley Land Fund believes that wildlife conservation can best be promoted through sound economic incentives for private landowners to protect and enhance the habitat diversity of habitats.

The Valley Land Fund information in this article is from the Valley Land Fund website and it is reprinted and edited in-part to fit within this article. To learn more about Valley Land Fund’s land conservation projects and partnerships, visit their website at Or, for more information about how you can help, please contact Valley Land Fund at (956) 686-6429 or



Stay Informed