Concho Water Snake Scientific Name: Nerodia paucimaculata Federal Status: Threatened, 9/3/1986, with federally-designated critical habitat • State Status: not listed Description whereas water snakes usually do not. stream to the FM 45 bridge over the The Concho Water Snake is small Also, an aroused cottonmouth will Colorado River (Mills and San Saba compared to most other water snakes, sometimes stand its ground, throw its Counties). This is a distance of about with adults rarely exceeding 3 feet in head upward and backward, and hold 233 river-miles. total length. This nonvenomous its mouth wide open, revealing a Apparently isolated lake popula- snake has four rows of alternating white “cotton-like” interior. tions have been found in E.V. Spence dark brown spots or blotches on its Reservoir and Ballinger Municipal back, two rows on each side. The Distribution Lake (formerly Lake Moonen). Con- coloration on its back is similar to a Historically, the Concho Water Snake cho Water Snakes have also been checkerboard of dark brown spots on occurred over about 276 river miles found at a number of sites in O.H. a gray, brown, or reddish-brown of the Colorado and Concho Rivers in Ivie Reservoir, and there are indica- color. The Concho Water Snake has a central Texas. The snake was first tions that this population is reproduc- light pinkish or orange belly that is collected from the South Concho ing. Scattered river populations unmarked or has somewhat indistinct River and Dove Creek, which are trib- occur along the Colorado River above spots along the sides. utaries to the Concho River west of Lake Buchanan, near the towns of San Angelo, Texas. When the sub- Regency, Harmony Ridge, Adams, and species was described in 1961, these records and one other on the Col- orado River south of Robert Lee in Coke County were the only known localities for this snake. The Concho Water Snake is endemic to Texas, which means it lives nowhere else in the world. It has one of the small- est distributions of any North American snake. The Concho Water Snake may once have been more widely distributed, but the E.V. Spence Reservoir upstream and Lake Buchanan Concho Water Snake © N. Scott downstream have inundated many Two other water snakes occur miles of river habitat at both ends of within the range of the Concho Water the current range. Scientists have Snake. Both the Diamondbacked Water estimated the historic range of the Snake (Nerodia rhombifer rhombifer) subspecies based on museum records and the Blotched Water Snake (Nero- and unpublished records supported by dia erythrogaster transversa) have specimens. The probable historic Bend. Recently, Concho Water Snakes dark markings on the back. However, range of this snake is estimated to have been found at all six artificial adult Diamondbacked and Blotched include, at a minimum, the Colorado riffles (fast-flowing, shallow water Water Snakes may be distinguished River from Spence Reservoir down- over a rocky bottom) constructed in from adult Concho Water Snakes by stream to the vicinity of Lake 1989 in the 17-mile stretch of the their larger size. The Diamondbacked Buchanan, Elm, Bluff, and Coyote Colorado River between the Robert Water Snake has a distinct black chain- Creeks (Runnels County), and the Lee Dam and Bronte. like pattern on its back. The Blotched entire Concho River (Tom Green and Although the Concho River has Water Snake has three rows of large Concho Counties) and its headwater been dammed and channelized within squarish blotches on the back, which tributaries, Dove Creek, Spring Creek, the City of San Angelo, a population are especially prominent in juveniles. and the South Concho River (Irion of Concho Water Snakes persists just As Blotched Water Snakes age, they and Tom Green Counties). below the Bell Street Bridge. They become darker in color and may Today, the Concho Water Snake have also been found about 4 river- appear to lack markings. occupies a restricted geographic range miles downstream from Bell Street The cottonmouth is another large in the Concho and Colorado River Dam. From this point they are pre- aquatic snake that may be confused Basins. The current distribution sent in all suitable habitats to the with the Concho Water Snake. The includes relatively continuous occupa- confluence with Ivie Reservoir, a dis- cottonmouth, a venomous snake, is tion of riverine habitat of the Col- tance of about 43 river-miles. usually uniformly black or dark brown orado River below the town of Bronte with little or no trace of a pattern, (Coke County), of Elm, Coyote, and Habitat although both neonates and juveniles Bluff creeks below Winters (Runnels Optimal habitat for the Concho Water are banded; neonates have a yellow or County), and of the Concho River Snake consists of free-flowing streams gold-colored tail tip, juveniles retain it from San Angelo (Tom Green County) but not as distinct. Cottonmouths downstream to its confluence with often vibrate their tails when excited, the Colorado River, and then down- Concho Water Snake 1 over rocky substrates, abundant rock Snakes. Although the type of vegeta- debris and crevices for shelter, and tion does not appear to be important, shallow riffles. Periodic scouring by its use depends on vegetation density floods is important in providing rela- and orientation. For example, preg- tively sediment free rock rubble and nant females seek basking sites pro- open banks. tected by thick vegetation. Larger Riffles, considered critical to trees and shrubs, such as pecan, juvenile survival, are characterized by cedar elm, and willow, with limbs shallow, fast-flowing water connecting that hang over water, provide basking deeper areas of quiet water. Riffles sites for juveniles and adults. Com- begin when the upper pool overflows mon bank and shoreline vegetation at a change in slope and forms used for cover and basking sites rapids. They end when the rapids include switchgrass, devil-weed aster, enter the next downstream pool. Rif- greenbrier, poison ivy, willow, salt fles often contain bars, shoals, or cedar, button bush, hackberry, pecan, islands separated by flowing water. cedar elm, and mesquite. Limestone bedrock shelves in Concho Water Snakes hibernate and along the stream channel seem to during the winter, either singly or in support the largest snake populations. small groups. Adults use a variety of The snakes forage and seek cover sites for hibernation, including cray- among the numerous splits, crevices, fish burrows, rock ledges, debris cracks, and jumbled stream cobble of piles, and concrete low water cross- shelf rock. Other rock, such as lime- ings. These sites are usually within stone boulders, can also provide suit- 20 feet of the water. Newborn snakes able habitat. have been found hibernating in areas Juvenile snakes are generally of loose rock and moist soil. restricted to rocky riffles. Neonates (newborn snakes) are most often Life History found in gravel bars or along the Concho Water Snakes are active pri- shoreline in areas where rocks range marily from March through October. Concho Water Snake river habitat in size from small cobbles to small Adult activity gradually decreases © USFWS Pat Connor boulders. However, some habitats during June and remains low until with thriving populations lack typical mid-September. Activity levels gravel bars. In these areas, juveniles increase again during late September use boulders and shelf rock for cover. and October. The snakes enter the During their second year, snakes hibernation site (hibernacula) during begin to use larger rocks, usually late October, although they can occa- medium to large boulders. sionally be seen on warm winter days Mature snakes use a much wider basking in the open. Newborn Con- range of habitats than juveniles. cho Water Snakes, born in August and Although adults forage in riffles, they September, are commonly found are known to use a variety of cover under rocks in late summer and early sites for resting, including exposed fall. In the heat of the summer, Con- bedrock, thick herbaceous vegetation, cho Water Snakes are active primarily debris piles, and crayfish burrows. Habitat along the shoreline of Spence Reservoir in the early morning and evening © UWFWS Alisa Shull During the latter stages of gestation, until about 9 p.m. gravid females occupy dense patches Research indicates that adult to minnows, large snakes consume of vegetation and brush piles. males move an average of 141 to mosquitofish, channel catfish, flat- In lake habitats, Concho Water 325 ft/day. Pregnant females move head catfish, gizzard shad, and sev- Snakes occupy areas of broken rock less, averaging 62 to 131 ft/day, with eral species of sunfish. The bullhead along the shoreline. Although they distances decreasing as parturition minnow, sheepshead minnow, and seem to prefer the shallower areas, approaches, and increasing again bigscale logperch were found to be they are occasionally found on steeper after the young are born. Linear dis- the dominant prey of snakes in shorelines where rock is present. As tances of river habitat occupied by Ballinger Municipal Lake. in river habitats, first-year snakes use individual snakes range from 689 to Concho Water Snakes catch prey smaller rocks for cover, while mature 1,542 feet. by remaining stationary near fish snakes use medium to large rocks. Long range movements of 3.1 and concentrations or by actively search- When available, dead shrubs and 4.5 miles have been recorded for juve- ing under and around rocks in riffles. trees killed by fluctuating water levels nile snakes dispersing from their birth- Juveniles are most often seen using are used as basking sites by juveniles place. In one instance, a snake moved the “sit-and-wait” strategy. and adults. At Spence Reservoir, 12 river-miles over a four-year period.