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A Survey of the Herpetofauna of the Comanche National Grasslands in Southeastern Colorado

Introduction


This document is a report of activities conducted in 1995-1997 which were funded in part (1996-1997) by the USDA-Forest Service (see Appendix 1). Activities reported here are directly associated with a larger survey of the herpetofauna of southeastern Colorado funded by the Colorado Division of Wildlife and the Great Outdoors Colorado program. All field and lab work with amphibians and reptiles was conducted as authorized by Colorado Division of Wildlife permits #95-0456, #96-0456 and #97-0456 (see Appendix 2).

Intent of Fieldwork Conducted

Southeastern Colorado is a sparsely inhabited region roughly 145 miles by 135 miles (nearly 20,000 square miles). Much of this area is plains grassland habitat (short-grass prairie) which supports a large number of terrestrial species, and amphibians and reptiles make up an important component of this grassland ecosystem. A moderate amount of distributional data for Colorado amphibians and reptiles exists as part of the CDOW databases on animal distribution in the state, but the last comprehensive summary of Colorado herpetofauna was published as Amphibians and Reptiles in Colorado (Hammerson, 1986). Recently, Livo (1995) and Livo et al (1996) have updated known county distributions of Colorado amphibians and reptiles, based on published reports of occurrences. Our work on the plains and canyonlands of southeastern Colorado has resulted in numerous county record localities: 12 records in 1995, 11 records in 1996, 6 records in 1997 and one state record in 1997. In addition, field work over the last three years has generated over 8000 locality records for 47 of 49 species of amphibians and reptiles known to occur in the southeastern portion of Colorado. We now have a much better set of baseline data from which to evaluate future changes in the herpetofauna of this part of the state. However, the distribution in Colorado of many species remains incompletely known due to the large area encompassed and a relative paucity of extensive, long-term inventory studies conducted. In addition, many areas have experienced and are currently experiencing extensive changes of the native grassland prairie, and much of this change is directly attributable to human activity. As human impact is likely to increase in the near future, a more complete inventory of the herpetofauna becomes more important to document the current range of the many species found in this part of Colorado before they become uncommon or are extirpated. In addition, many of the species of amphibians and reptiles are primary or secondary consumers, and the status of their populations can serve as "early warning" signals of larger unseen changes likely to affect other animals soon (including humans). The presence of several of the more easily disturbed species also can serve as indicators of overall habitat quality and health. Based on three years of field data and observations, areas of particularly high abundance of the three main species of concern (short-horned lizard, Texas horned lizard and massasauga rattlesnake: CDOW definition) and/or of particularly high herpetofaunal abundance and diversity were identified, and a concerted effort should be made to protect the integrity of these areas. Loss of appropriate habitat due to many causes is the major threat to all of Colorado's native species, and amphibians and reptiles, being much less vagile than most game species, are particularly vulnerable. Southeastern Colorado is inhabited by approximately 49 species of amphibians and reptiles (Hammerson, 1986). Although the southeastern part of the state accounts for roughly 1/4 of the total state area, this region supports representatives of nearly 77% of the herpetofaunal species known to occur in Colorado. The southeast is represented by 1/1 species of salamander, 13/17 species of frogs, 5/5 species of turtles, 9/16 species of lizards and 21/25 species of snakes. The Comanche National Grasslands, which encompasses large tracts of land within southeastern Colorado, contains diverse habitat which is occupied by 1/1 species of salamander, 11/17 species of frogs, 5/5 species of turtles, 7/16 species of lizards and 21/25 species of snakes (Hammerson, 1986; Mackessy, 1997 and current work). The Grasslands therefore contains habitat appropriate for most species of amphibians and reptiles (~92%) which are found in southeastern Colorado, and this area has the potential to serve as a refuge from (primarily) human-caused disturbances in habitat. Most of these species are retiring by nature and many are highly seasonal, making it difficult to obtain accurate population estimates from short-term studies. However, extensive fieldwork at all times of the active season will increase the likelihood of encountering retiring or rare species. Coupled with multiple year surveys, these studies can provide population estimates which are necessary to manage properly this often overlooked component of the Colorado fauna. During the course of this study, we recorded the occurrence and location of all species of amphibians and reptiles. Three species of special concern (CDOW definition) were the primary focus, and fieldwork was concentrated in areas known to be occupied (historically) by these species or found to be appropriate habitat (prior fieldwork, 1995) for these species. For the purposes of this report, the area of focus is the Comanche National Grasslands, a large area in southeastern Colorado which is in part under the jurisdiction of the USDA/US Forest Service (much of the area included in the Grasslands boundary is private). During the survey period, 36 species of amphibians and reptiles were encountered, and several additional species were found in adjacent areas with habitat similar to that within the boundaries of the Grasslands. The information included here is provides baseline data on the occurrence and relative abundance of many species of amphibians and reptiles in the Grasslands, and this data is also part of the larger data set being provided to the CDOW. It should be noted that for many species, habitat immediately outside of the boundaries of the Grasslands is also of excellent quality and is occupied by R-2 sensitive species/species of special concern.

Species Focus

This survey was conducted as part of a larger survey funded by CDOW/GOCO which has as its primary intent to provide detailed information concerning three species of special concern (CDOW definition). These species include the short-horned lizard (Phrynosoma douglassii), the Texas horned lizard (Phrynosoma cornutum) and the desert massasauga rattlesnake (Sistrurus catenatus edwardsii). The two horned lizards have been subject to overcollection for use in the pet trade and have also suffered habitat loss, and the current distribution of these species in southeastern Colorado was evaluated. Short-horned lizards are broadly distributed throughout the state, but appear largely absent from lower elevation habitat of extreme eastern Colorado. The Texas horned lizard is confined to the southeastern corner of the state, but it is much more widely distributed to the south, including much of Arizona, New Mexico and Texas. It is considered threatened in all parts of its current range except Colorado. The massasauga rattlesnake is broadly distributed from eastern New York to southeastern Arizona, and in Colorado it occurs as an apparently disjunct population centered in southeastern Lincoln Co./western Kiowa Co. The massasauga has also suffered loss of habitat and has been collected indiscriminately for the pet trade; in addition, like most snakes, particularly venomous species, it is often killed on sight. The massasauga is considered threatened or endangered over most of its range in the U.S. and in Canada, and it is likely in decline in Colorado as well. Historically, the Colorado snakes have been regarded as an intergrade between western and desert subspecies, but this conclusion is based on a very small number of specimens (Maslin, 1965). A separate study conducted by my lab (not funded by these projects) is investigating the genetic affinities of the Colorado massasaugas with other populations of this snake. Based on extensive morphometric data and more limited venom protein molecular data, massasaugas in Colorado should be considered the desert massasauga (Sistrurus catenatus edwardsii). Preliminary results of this work have been presented (see Appendix 6), and a formal analysis is forthcoming. Both the Texas horned lizard and the massasauga were observed on the Comanche National Grasslands during the survey period. In addition, one species of amphibian (Ambystoma tigrinum) and eight species of reptiles (Kinosternon flavescens, Phrynosoma cornutum, Arizona elegans, Diadophis punctatus, Lampropeltis triangulum, Leptotyphlops dulcis, Rhinocheilus lecontei and Tropidoclonion lineatum) which are listed as U.S. Forest Service R-2 sensitive species are known to occur in southeastern Colorado, and specific attempts to obtain locality data on these species were made. Finally, in the process of surveying for the above-listed species, many other amphibian and reptiles were encountered. Fieldwork is extremely time-intensive, and although the eleven species listed above were the primary focus, many other species of amphibians and reptiles were observed and recorded during this study. On numerous occasions we observed rare species and/or large numbers of more common species. This report will also contain data on the other 25 species of amphibians and reptiles encountered (Appendix 4), and photographs of many species are included in Appendix 7. Threats to the well-being of populations of amphibian and reptile species can be generalized into three categories: 1) natural cycles of species attrition (causes varied), 2) loss of appropriate habitat due to human interventions and 3) direct persecution by humans. Of these three, the second, loss of habitat, is probably most severe and most critically threatening, and it is here that this survey can assist most in the management of these species. By identifying regions with viable populations of these animals , recommending conservation of state-owned lands containing these species and working with local landowners, we hope to assist in the conservation of the Colorado's diverse herpetofauna.

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