Wildlife of the Concho Valley

Wildlife of the Concho Valley

by Terry C. Maxwell

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The Concho Valley, named from the abundant mussel shells found in its principal river by seventeenth-century Spanish explorers, occupies a transitional position between the Chihuahuan Desert to the west and the Balcones Canyonlands to the east. As veteran field biologist and educator Terry C. Maxwell notes, the region has experienced wide-ranging changes in the…  See more details below


The Concho Valley, named from the abundant mussel shells found in its principal river by seventeenth-century Spanish explorers, occupies a transitional position between the Chihuahuan Desert to the west and the Balcones Canyonlands to the east. As veteran field biologist and educator Terry C. Maxwell notes, the region has experienced wide-ranging changes in the makeup of its vertebrate populations, especially in the decades since farming and ranching began here in earnest, in the mid- to late 1800s.

In Wildlife of the Concho Valley, Maxwell provides the first comprehensive summary of the animal life in this undercovered region of the state, which also happens to be his home territory. Uniquely qualified after a lifetime of study and field work, Maxwell places the region in its biogeographic context and then charts the history of vertebrate investigation there from the seventeenth century to the present. Following this ecological and historical perspective are accounts of all the fishes, amphibians, reptiles, birds, and mammals reliably known by zoologists and naturalists to have occurred in the Concho Valley over the past 150 years. The species accounts include Latin and English names; distribution and abundance status; remarks, where the author elaborates on habitat preference, behavior, and other aspects of natural history; specimens reported; and subspecies and synonyms.

This important work of traditional natural history is liberally illustrated with Maxwell’s own drawings, photographs, and maps. An invaluable reference, Wildlife of the Concho Valley is a major contribution from one of the state’s most respected biologists and teachers.

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Editorial Reviews

Mark Lockwood

"I was delighted to receive a copy of the just published Wildlife of the Concho Valley by Dr. Terry Maxwell . . . As the title implies, it covers the occurrence of all of the vertebrates from that region of our state.  This 10+ county area is a real mixing pot with an interesting conglomeration of species.  It addition it is beautifully illustrated with Dr. Maxwell's origin pin and ink drawings.  If consider yourself a naturalist interested in the natural history of Texas, book was written for you."-Mark Lockwood, author of Basic Texas Birds
Dr. Keith Arnold

“Terry Maxwell is as close as there is to the 'holistic' naturalist; that is, he has broad interest across a wide variety of natural history topics. Such is the case in this book on the Concho river valley. Terry presents an historical synopsis of changes in habitat and species composition that few modern regional books encompass. He’s a pretty fair artist as well!”—Keith Arnold, Professor Emeritus, Texas A&M University
Dr. David J. Schmidly

“This is the most important original and comprehensive regional study yet to appear of the interesting Concho Valley region of western Texas. Terry Maxwell is one of the few Texas naturalists with the breadth of knowledge to write about all of the wildlife of this region–from fishes to mammals. He writes about the Concho Valley with the love and understanding of a place where he grew up as a boy and worked throughout his professional career. This book constitutes an important reference for anyone interested in Texas natural history.”—David J. Schmidly, Texas naturalist and former president, Texas Tech University, Oklahoma State University, and University of New Mexico

Product Details

Texas A&M University Press
Publication date:
W. L. Moody Jr. Natural History Series, #48
Product dimensions:
6.40(w) x 9.50(h) x 0.90(d)

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Wildlife of the Concho Valley

By Terry C. Maxwell

Texas A&M University Press

Copyright © 2013 Terry C. Maxwell
All rights reserved.
ISBN: 978-1-62349-006-5



From Dr. Notson's nineteenth-century days at Fort Concho to the current intense investigations by university faculty and students and naturalists, information on the vertebrate animals in the modern Concho Valley of Texas has grown. It is time to make some sense of all that has been learned and to tell the story of the animals in this region.

Rounding up the information has been a decade-long effort. The published and unpublished observational records of dozens of naturalists and the specimen records in forty-six museums and private collections are the raw material for the accounts here of 606 vertebrates that occur or at least did occur within history. Most of this book is dedicated to the species accounts that emphasize status and distribution of those fishes, amphibians, reptiles, birds, and mammals. In addition there are brief descriptions of the Concho Valley today


The Concho Valley is transitional in climate and plant and animal communities between the Chihuahuan Desert to the west and the Balconian canyonland woodlands to the east. It takes its name from the Concho River, a tributary of the upper Colorado River of Texas. Some of the earliest Spanish expeditions that penetrated what now is Texas traveled to these river valleys, where they found Native Americans, groves of large pecan trees, unimaginable numbers of bison, and beautiful Concho pearls. The shell of the mussels that produce the pearls is called concha in Spanish, giving the river its modern name. Before railroads, the shortest distance from settled Central Texas westward without water to the Pecos River was along the Middle Concho River and Centralia Draw, and in the nineteenth century, Butterfield Overland stagecoaches, Apaches, Comanches, ranchers, and vast herds of bison were encountered on that route.

As delimited here, the Concho Valley (Map 1) occupies about 29,756 sq. km (11,500 sq. mi.—233 km or 145 mi. east to west, 148 km or 92 mi. north to south) of the northwestern Edwards Plateau and the southern margin of the Central Great Plains level III ecoregion. Included are all of 10 counties (Coke, Concho, Glasscock, Irion, Menard, Reagan, Runnels, Schleicher, Sterling, and Tom Green) as well as the northeastern third of Crockett County (Map 1). The land rises from a low elevation of about 450 m (1,500 ft.) at the eastern margin to about 890 m (2,900 ft.) at the west. The characteristic landforms are tableland, limestone slopes, and outwash plains, all drained largely by the upper Colorado River of Texas and its Concho and San Saba tributaries.

Lands with public access for viewing birds and other wildlife are not extensive in the Concho Valley. The largest areas are San Angelo State Park, which is around Lake O. C. Fisher on the northwest border of San Angelo, and parks and other lands around Lakes O. H. Ivie in Concho County, E. V. Spence in Coke County, and Nasworthy and Twin Buttes in Tom Green County. County and city parks give access to riparian woodlands along Concho system streams. The city park system in San Angelo is extensive along the North Concho River and well worth the time walking the excellent paths. The larger of the parks outside of San Angelo are Pugh Park on the South Concho River in the town of Christoval, Tom Green County; Harper Park on the North Concho River just southwest of Water Valley, Tom Green County; Foster Park on Spring Creek, 2 mi. south of Tankersley, Tom Green County; Bridge Park and Stockpen Crossing Park in the town of Menard, Menard County; and Ballinger City Park in the town of Ballinger, Runnels County.


Twice in the past 280 million years, in the Permian and Cretaceous geologic periods, what is now the Concho Valley was covered by sea. Sediments deposited on the floors and at the margins of those seas are today the local bedrock. The limestones from the great Western Interior Seaway of the middle to late Cretaceous (roughly 100 million to 65 million years ago) cap the older sandstones, conglomerates, and gypsums of the Permian. At many locations the Cretaceous limestones are filled with fossil marine invertebrates that lived in the ancient sea.

Rivers have been lengthening east to west over the last several million years and eroding the land surface. In the longer-eroded east, the Cretaceous limestone cap is shallower, or even absent, and the Permian rock more exposed.

Many of the region's soils are derived from limestone parent rock, leaving them at least moderately alkaline. Native plants that support our native animal communities are adapted to that soil nutrient condition, one ultimately established by those ancient seas (Grenda 1982, Sellards et al. 1932, Wiedenfeld and Flores 1976).

Streams, Springs, and Reservoirs

Streams flow generally eastward in a dendritic pattern to enter the Colorado River (Map 2). They are moderate-grade streams whose flow rates fluctuate wildly between drought and wet weather events. Major floods (notable historic ones in 1853, 1882, 1899, 1906, 1925, 1936, 1938, 1957, and 1988) stimulated efforts to protect the region from flooding by the construction of the major impoundment dams west of San Angelo. In severe droughts, most streams are reduced to separated pools with little if any surface flow. Streams are the natural habitat for all of our native fishes. They also support many of our land animals, particularly with their riparian stands of trees that have attracted numerous eastern woodland animals into this otherwise dry region.

Major drainages are the Concho and San Saba Rivers. The Concho River forms in San Angelo where the North Concho River joins the South Concho and Middle Concho. It then flows eastward to its junction with the Colorado River, which today is inundated by Lake O. H. Ivie. The dry Centralia Draw begins slightly west of the region and drains to the Middle Concho River. Important flowing, or sporadically flowing, tributaries of these streams are Big Rocky, Spring, Dove, Lipan, and Kickapoo Creeks.

The San Saba River drains the southeastern corner of the region, also flowing eastward to join the Colorado outside of the Concho Valley. A major local tributary of the San Saba is Brady Creek in southern Concho County. The Colorado River enters the region in northwestern Coke County and exits at Lake O. H. Ivie in southeastern Runnels County. Its major tributary is Elm Creek. In southwestern Schleicher and northeastern Crockett Counties, largely dry draws run southward to the Dry Devils and Pecos Rivers.

Of major importance to perennial stream flow are springs that surface mostly from the Edwards-Trinity Aquifer. On the San Saba River, Government Spring near old Fort McKavett and Wilkinson Springs, which form Clear Creek, establish much of the river flow in Menard County.

Where the Edwards Plateau meets the Central Great Plains, an east-west line of springs (Kickapoo, Lipan, Anson, Dove Creek, Seven, and Kiowa) have been crucial to flora and fauna and to the human history of the region. On the North Concho, several springs (including historic Shelving Rock) are now wholly or mostly dry (Brune 1975).

Beginning in the late nineteenth century, particularly following the devastating droughts of 1886 and 1918, ranchers began constructing pushed-earth stock tanks to catch rainwater runoff and concrete tanks filled by windmill pumping. The now numerous stock tanks have had a major influence on the local distributions of vertebrates, allowing many native animals more regularly to occupy terrain distant from natural water sources. Of even more consequence to animals (aquatic and terrestrial) has been the impoundment of reservoirs. There are no natural perennial lakes in the Concho Valley, and yet since the mid-twentieth century, introduced fishes and waterbirds have flourished in and around reservoirs. Those large enough to note and their dates of construction and location are Lake Nasworthy (1930), O. C. Fisher Lake (1951), and Twin Buttes Reservoir (1963) in Tom Green County; Lake O. H. Ivie (1989) in Concho County; Ballinger City Lake (1947) in Runnels County; and Oak Creek Reservoir (1950) and E. V. Spence Reservoir (1969) in Coke County (Holden 1928, Lintz et al. 1993). The impoundments have greatly altered stream flows, most notably in regard to ending flushing flows following heavy rainfall. Those scouring flows have been largely absent in the past half-century, with subsequent buildup of vegetation in stream channels (Forstner et al. 2006).


The climate of the Concho Valley is subtropical subhumid in the east and subtropical steppe (semiarid) in the west. It is a continental climate (with significant seasonal variation) influenced by tropical maritime moisture from the Gulf of Mexico and cold Canadian air masses. On any day temperatures are fairly similar throughout, with a recent mean July maximum of 96.2°F and a mean January minimum of 30.6°F. The average number of days with 100°F or higher has been 18 in recent decades, but in the extreme summer of 2011, there were 100 days with at least 100°F. Many animals are behaviorally adapted to be most active at times when they can avoid summer high daytime temperatures. On the other hand, winters tend to be mild, and only some ground squirrels, among the mammals, hibernate. Cold-sensitive armadillos can find warm enough periods on most winter days to forage out of their burrows. With an average annual snowfall of only 2.9 in., granivorous birds winter here, some years in great number, unhindered by snow cover in their search for seeds.

Rainfall, however, does vary noticeably. In the eastern counties annual average precipitation is about 24–25 in., and in the western counties it declines to about 18–19 in. In this interior region of spring and fall maxima of precipitation, highest rainfalls are April to early June and again September to October. Much of the rain comes in convective thunderstorms that can be severe, with hail and high winds. The 1995 Memorial Day hailstorm killed hundreds—perhaps thousands—of Inca Doves and other birds in San Angelo.

The high evaporation rate (in excess of 63 in. annually) means that there tends to be a relentless moisture deficit. None of those climate values, however, reveals what is ultimately consequential about the Concho Valley climate: periodic droughts, often of multiple-year duration. They can be devastating for native plants and animals as well as for people and their crops and livestock. Memories of them and their extended effects are long. One of the most famous recent novels in western literature is The Time it Never Rained, by Elmer Kelton of San Angelo. Among the most severe droughts, for meager precipitation and long duration, were those of 1885–87, 1916–18, 1933–34, 1946–48, 1951–56, and 1980–83, and most recently a series of punctuated droughts from 1999 through 2011.

In the catastrophic drought of June 1885 to May 1887, cattle died by the thousands, and many people abandoned their homes. To compound the lack of rainfall, a severe blizzard hit in early 1886, killing thousands more of the already starving cattle. The devastation altered many of the ranching practices of the previous 25 years. Undoubtedly also, populations of most wild animals declined as vegetation withered in the drought. Even hardy mesquites and junipers died in the 1946–48 dry spell (Bomar 1995, Holden 1928, Larken and Bomar 1983, Wiedenfeld and Flores 1976).

In the 7-month period November 2010 through May 2011, with little to no rain at many Concho Valley locales, brush fires burned over 68,826 ha (170,000 acres) of canyons, badlands, and semiarid Edwards Plateau. The resulting blackened terrain was reminiscent of the written descriptions of burned land by travelers through the region in the midnineteenth century (Bryan 1849, Bartlett 1853).

Land Ecoregions

The Concho Valley supports two major biomes or plant formations: Pygmy Conifer Woodland and Mesquite-Grassland. The biotic provinces represented are the Balconian (basically, the Edwards Plateau) and the Kansan (the Rolling Plains). In this work, however, the new map of the ecoregions of Texas, prepared in 2004 for the US Environmental Protection Agency (EPA), best characterizes the ecological associations in the Concho Valley (ftp://ftp.epa.gov/wed/ecoregions/tx/tx_front.pdf).

The Concho Valley is in the Great Plains level I ecoregion of North America. At level III for Texas, four ecoregions are represented here: Edwards Plateau, High Plains, Southwestern Tablelands, and Central Great Plains. The level IV subdivisions (Map 3) are presented below (ftp://ftp.epa.gov/wed/ecoregions/tx/tx_eco_lg.pdf; Aldrich 1967, Griffith et al. 2004, Maxwell 1979a, Maxwell 1995).


The southern and western two-thirds of the Concho Valley are in the Edwards Plateau, an area of flat to rolling terrain with erosional slopes down to stream floodplains. Soils typically are shallow and stony. Land use is primarily rangeland for sheep, goats, and cattle and recreational hunting. Two subdivisions are distinct. The eastern portion is the Edwards Plateau Woodland (Map 3, area 6). Here, rainfall is greater than to the west, allowing for more gently rolling limestone dissolution slopes. The conspicuous woody vegetation is plateau live oak (Quercus fusiformis), Ashe juniper (Juniperus ashei), Pinchot's juniper (J. pinchotii), and honey mesquite (Prosopis glandulosa). In the nineteenth century it was open savannah of oak and juniper, but today, where not successfully controlled, it has often developed into juniper-mesquite brushland. Running through the woodland is the San Saba River, with impressive groves of tall pecans (Carya illinoinensis). This woodland has produced more goats and sheep than any other area of the Concho Valley. In 2008, three of the counties (Concho, Menard, and Schleicher) in the Edwards Plateau Woodland had 65 percent of all goats and 51 percent of all sheep raised that year in the region.

The plateau west and northwest of the woodland and occupying a larger portion of the Concho Valley is Semiarid Edwards Plateau (Map 3, area 2). Erosional slopes here tend to be more vertical as a result of less rainfall and reduced dissolution erosion. Live oak is less common, and the characteristic woody vegetation is a juniper-mesquite shrubland. Other aridland shrubby plants of the region are lotebush (Ziziphus obtusifolia), javelina bush (Condalia ericoides), littleleaf sumac (Rhus microphylla), tarbush (Flourensia cernua), and agarita (Mahonia trifoliolata). Cacti—prickly pears (Opuntia spp.) and cholla (Cylindropuntia spp.)—are common as well as yuccas (Yucca spp.) and even sotol (Dasylirion wheeleri); a hint of the Chihuahuan Desert. The North Concho and Middle Concho Rivers carry a riparian gallery woodland of pecans, thinning westward into Sterling and Reagan Counties, as far west as they occur naturally in Texas. Most riparian tree growth west of the pecan limit is netleaf hackberry (Celtis reticulata) and river walnut (Juglans microcarpa).


Little of this ecoregion is present in the Concho Valley; only portions of Reagan and Glasscock Counties are in the High Plains. To the north of our region the High Plains ecoregion extends to the Texas Panhandle, eastern Wyoming and western Nebraska. The overwhelming majority of the original short-grass plains formerly populated by bison, Pronghorn, and prairie dogs is now in cultivation for cotton, sorghum, and corn. All but a trace of this plains region in the Concho Valley is in the subdivision called the Arid Llano Estacado (Map 3, area 1), where rainfall approaches the aridity of the eastern Chihuahuan Desert. Mesquite brush is common, as are cacti, but much of the area is now in irrigated cropland. This is the only area in the region with an abundance of playas, or temporary ponds, that fill and dry with the cycle of wet and drought years.


Much of the northern boundary of the Concho Valley is in this topographically complex ecoregion of broken terrain, which is a southeastern extension of the bluffs and badlands at and below the Caprock Escarpment, the eastern rim of the Llano Estacado. The subdivision here is the Caprock Canyons, Badlands, and Breaks (Map 3, area 3). Steep slopes, often with relief of 120–150 m (400–500 ft.) or more, lead from high rim rock bluffs down to steeply eroded draws and plains. The woody vegetation is Pinchot's juniper, Ashe juniper, mesquite, Mohr oak (Quercus mohriana), bastard oak (Q. sinuata var. breviloba), sumacs (Rhus trilobata and R. lanceolata), and ephedra (Ephedra antisyphilitica). Plateau live oak is found on the eastern tabletops. Prickly pear cactus is locally abundant in dense brushland on the outwash and flood plains. The Colorado River drains the area and supports sparse stands of pecan and increasing amounts of nonnative invasive salt cedar (Tamarix spp.).


Excerpted from Wildlife of the Concho Valley by Terry C. Maxwell. Copyright © 2013 Terry C. Maxwell. Excerpted by permission of Texas A&M University Press.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

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Meet the Author

TERRY C. MAXWELL, an award-winning teacher whose stature as an ornithologist is recognized statewide, is professor and curator of birds in the department of biology at Angelo State University in San Angelo.

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