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

Results and Conclusions


General Observations

1997 Season

As a result of observations of early season activity by several species in 1996 (some frogs, lizards and snakes were already active by 15 April), the 1997 field season began 1 April and extended to the end of October. Amphibian and reptile activity is dependent primarily on temperature and relative humidity (rainfall), and most species did not become active until mid-April. Fall weather conditions were extremely mild this year, and several species, including the bullsnake, plains garter snake, massasauga rattlesnake and prairie rattlesnake were observed on the surface as late as 30-31 October 1997. On 21 November, the field crew observed one radioed massasauga on the surface (air temperature 13°C). We are continuing to monitor radioed massasaugas in Lincoln County, and I predict that we will observe some surface activity if mild conditions occur in early December, as weather was in 1996.

In 1997, over 3000 observations and collections of amphibians were made in southeastern Colorado, and over 420 individual locality records for 36 species were recorded in the Comanche National Grasslands during the total survey period (Appendix 4). County distributional records were obtained for Chelydra serpentina, Phrynosoma cornutum, Phrynosoma douglassii, Lampropeltis getulus, Lampropeltis triangulum and Sistrurus catenatus (Appendix 5). One state record, for the Texas rat snake (Elaphe obsoleta lindheimeri), was obtained in Kiowa Co.

1996 Season

Based on observations in 1995, the 1996 season was initiated on 15 April. In 1996, over 4500 observations/collections of amphibians and reptiles were obtained for southeastern Colorado. Forty-four different species were observed in the total survey area, and three of these, the Great Plains narrowmouth toad (Gastrophryne olivacea), Couch's spadefoot toad (Scaphiopus couchi) and the common king snake(Lampropeltis getulus), are poorly known in Colorado. Significant range extensions, representing eleven county records, were obtained for Gastrophryne olivacea, Pseudacris triseriata, Rana catesbeiana, Spea multiplicata, Chrysemys picta, Lampropeltis getulus, Lampropeltis triangulum, Rhinocheilus lecontei, Sistrurus catenatus, Thamnophis cyrtopsis and Tropidoclonion lineatum (Appendix 5). Nearly three hundred specimens of 27 species of amphibians and reptiles from southeastern Colorado were collected and entered into the University of Northern Colorado Museum of Natural History preserved Herpetology Collection; all of these specimens were salvaged road killed animals, and most are in good to excellent condition.

1995 Season

The 1995 field season began 15 May and ended 15 October, and over 2400 observations/collections of amphibians and reptiles were made. Forty-three different species were observed, and we obtained multiple sightings for most species. One specimen, the Texas blind snake (Leptotyphlops dulcis) represents only the fourth record of occurrence of this species in Colorado. In addition, significant range extensions were discovered for Pseudacris triseriata, Eumeces obsoletus, Arizona elegans, Coluber constrictor, Diadophis punctatus, Rhinocheilus lecontei, Sistrurus catenatus and Tantilla nigriceps. These range extensions represent nine county records.

US Forest Service R-2 Sensitive Species

Distributional data was obtained for all species of amphibians and reptiles on the US Forest Service R-2 Sensitive Species list which are known to occur on the Comanche National Grasslands except the yellow mud turtle (Kinosternon flavescens), the plains milk snake (Lampropeltis triangulum) and the Texas longnosed snake (Rhinocheilus lecontei); numerous specimens of the latter two species were encountered in habitat near/adjacent to the boundaries of the Grasslands. For each of the species found within the Grasslands boundaries, an account is given below; additional distributional data outside the Grasslands is provided for several species which were encountered less frequently. A complete list of all species of amphibians and reptile encountered on the Grasslands is given in Appendix 4.

Ambystoma tigrinum - 9 specimens

Tiger salamanders were encountered on several occasions crossing roads during heavy rains; it is likely that they move from rodent burrow refugia to ponds and move between ponds during these conditions. Tiger salamanders also utilize stock ponds for breeding, and several ponds near the junction of David Canyon Rd. and Rourke Rd. (northern section) contained larval salamanders in late spring of 1996 and 1997. As long as ponds of this type are available to salamanders, and they are not fouled by extensive cattle use, it is likely that tiger salamander populations will remain stable on the Grasslands.

JPG -- Barred tiger salamander
Barred tiger salamander (Ambystoma tigrinum mavortium). This is the only species of salamander known to occur in Colorado, and it is broadly distributed across the plains. At times of high rainfall and particularly following metamorphosis, numerous individuals may be encountered crossing roads.

Phrynosoma cornutum - 65 specimens

Texas horned lizards were one of the species of primary focus for the larger survey, so much more effort went into locating animals and appropriate habitat. Both sections of the Grasslands contain good shortgrass habitat with loose sandy soils favorable for Texas horned lizards, and these lizards were frequently encountered on burms or crossing dirt roads. Texas horned lizards are most active on warm to hot days in late June through early September. The Texas horned lizard is threatened primarily by habitat loss/conversion, and its habit of basking on roads ensures that mortality along roads, paved and dirt, will be high. Numerous natural predators take horned lizards, particularly raptors, and a Texas horned lizard was found pinned to a barb-wire fence by a shrike (northern section, Rourke Rd.). Horned lizards have also historically been threatened by collection for the pet trade, and removal of lizards for this purpose will likely continue to pose a threat to populations in accessible areas.

Arizona elegans - 3 specimens

The plains glossy snake is moderately common in much of southeastern Colorado, but it is less abundant south of the Arkansas River drainage. The three specimens found on the Grasslands were all observed in the northern section just south of La Junta. Many glossy snakes have also been found north of La Junta (near the junction of Highways 109 and 96) and into Lincoln County, where they are moderately common. They are typically nocturnally active and may be out on roads later at night. One specimen was found north of the Grasslands in early October, indicating that its typical activity period may extend well into the fall.

JPG -- Kansas glossy snake
Kansas glossy snake (Arizona elegans elegans). This large constrictor is moderately common in shortgrass prairie habitat and may be found later at night and at cooler temperatures. The smooth scales and clean white ventral surface clearly distinguishes them from bullsnakes.

Diadophis punctatus - 15 specimens

Ringnecked snakes are moderately common under logs and litter in the canyonbottoms in the southern section of the Grasslands, particularly Cottonwood and Carrizo Canyons in Baca County and the canyons of the Black Mesa of Las Animas County. They are secretive snakes which are near the surface only when soil moisture is relatively high, and they were most frequently found in May and June. Ringnecked snakes are most abundant in sparsely populated areas, and as long as overgrazing by cattle is prevented, populations of this snake in Colorado are probably stable.

JPG -- Prairie ringneck snake
Prairie ringneck snake (Diadophis punctatus arnyi). These secretive fossorial snakes are most commonly found beneath logs or rocks when soil moisture levels are high. Note the characteristic defense posture, with the tail inverted and curled; this display may invoke a startle response in potential predators.

Leptotyphlops dulcis - 1 specimen

This species is highly secretive, typically nocturnal and is probably uncommon in specific habitat in southeastern Colorado. The single specimen encountered was found in Cottonwood Canyon in the southern section of the Comanche National Grasslands, and it crawled into camp late at night (July 1995). The specimen was collected, photographed and returned to the site of capture. These snakes are specialists on ants and termites and are rarely encountered on the surface except after rains. Specific conditions favored by these snakes which elicit surface activity are unknown, but in California, they may be locally common on a specific night at a specific site and then not seen again during an entire season (S. Sweet, pers. comm.). Only four-five specimens of this snake have been found in Colorado.

JPG -- Texas blind snake
Texas blind snake (Leptotyphlops dulcis). Blind snakes are very uncommon and localized in extreme southeastern Colorado. This specimen (approximately the fifth recorded for Colorado) crawled into camp in Cottonwood Canyon at night-what specific conditions are necessary for surface activity are wholly unknown.

Tropidoclonion lineatum - 8 specimens

Lined snakes are predictably encountered near streams and areas with abundant surface moisture in southeastern Colorado. Specimens were encountered in Picture Canyon and Cottonwood Canyon in the southern section, and in Vogel Canyon in the northern section of the Grasslands. Logs, rocks and other cover, particularly if they are within the stream channel but are not flooded, serve as refugia for these snakes. They may also be found in areas which are shaded from extreme diurnal exposure (such as near abandoned buildings) which offer shelter, and boards are used commonly as refuge from drying surface conditions, particularly during the spring and early summer. Lined snakes look superficially like the wandering garter snake (Thamnophis elegans vagrans), but they attain a smaller adult size and have paired black spots on the ventral surface. Populations of the lined snake are likely stable in Colorado as long as stream channels are not diverted and cattle are kept from grazing and watering at stream beds.

JPG -- Lined snake
Lined snake (Tropidoclonion lineatum lineatum). Lined snakes were encountered most frequently near water and can usually be found in Vogel Canyon (northern section) except during the driest parts of summer.

JPG -- Lined snake
Lined snakes are superficially similar to several species of garter snakes, especially wandering garter snakes. Note the paired black ventral markings; wandering garter snakes occasionally showing dark ventral pigmentation, but it is never regular as in lined snakes. In addition, lined snakes are much smaller, with an adult maximum length of approximately 525 mm (usually much smaller).

Observations on R-2 Species Not Observed Within the Comanche National Grasslands

Plains milk snake (Lampropeltis triangulum)
Milk snakes are probably moderately common in much of southeastern Colorado, but based on my experience with this species in eastern Colorado, their activity patterns are limited to periods when surface moisture/water is relatively high. They have been encountered crossing Highway 109 just south of La Junta (but outside the Grasslands boundaries) on several occasions. Three live specimens of milk snakes were observed in Lincoln county, and all were encountered crossing roads after rains. In 1996, ten milk snakes were documented in southeastern Colorado, and one, from extreme northcentral Baca County, was a county distributional record. Milk snakes were also found in Cheyenne County (3), Elbert County (1), Lincoln County (2), Otero County (1) and Prowers County (2). Soil moisture levels were typically higher (i.e., recent rain) when most of these specimens were found.

JPG -- Plains milk snake
Plains milk snake (lampropeltis triangulum gentilis). This brightly colored harmless snake is responsible for the persistent myth that venomous coral snakes occur in Colorado. Milk snakes appear to be most frequent in sandy soils, and surface activity is greatest when soil moisture levels are relatively high.

Longnose snake (Rhinocheilus lecontei)

No longnose snakes were found on the Comanche National Grasslands during the survey period. However, several were found in areas immediately adjacent to the Grasslands borders (both sections), and it is likely that longnose snakes occur uncommonly on the Grasslands. Longnose snakes were found in Otero County (two), one in Kiowa County and one in Baca County. The Kiowa County specimen, taken DOR on Highway 287 on 5 September 1996, was a county distributional record which is also north of the Arkansas River drainage. Two specimens were found in Prowers county and one was found in Cheyenne County; the latter specimen is also a county record (see Appendix 5). This sample, a road-killed specimen entered in the UNC-MNH Herpetology collection, extends the known range of the longnose snake over 35 miles north of its previous known range in eastern Colorado (Arkansas River and south). It is also a secretive, nocturnal species, and it may be more common than it appears because of these activity patterns.

JPG -- Texas longnose snake
Texas longnose snake (Rhinocheilus lecontei tesselatus). Although no longnose snakes were found on the Comanche National Grasslands during the study period, several specimen were found in the same shortgrass prairie habitat in adjacent areas, and I would except that it is an uncommon member of the herpetofauna of the Grasslands.

Primary species of concern - potential candidates for protected species status: CDOW designation

Texas horned lizard (Phrynosoma cornutum)

Texas horned lizards (Phrynosoma cornutum) were frequently encountered on both sections of the Grasslands in shortgrass prairie habitat of good quality (not farmed, overgrazed, etc.), and much of the range statewide is within the Grasslands. A total of 60 horned lizards were found on the Comanche National Grasslands during the survey period (see Appendix 4). Live specimens were measured, PIT-tagged and released at the site of capture, and all road-killed specimens were retained. All preserved specimens were entered into the UNC Museum of Natural History (UNC-MNH) preserved Herpetology Collection.

Texas horned lizards appear to be much more heat-tolerant (and perhaps dependent?) than short-horned lizards, and their main activity period is in the hottest summer months. It is of interest to compare horned lizard activity profiles, because Texas horned lizards are encountered most frequently when short-horned lizards are encountered least frequently. At the beginning of the season, Texas horned lizards were active from approximately 11:00-17:00 hours (mid-late June). In July and August, lizards were active from 8:00-19:00 hours with a period of inactivity between 12:00-17:00 hours. By early to mid September, Texas horned lizards appear to enter hibernacula, and they are no longer observed. They are most abundant on sandy soils with sage (Artemisia) and large areas of bare ground, and they are severely affected by conversion of lands to farming. Much of the appropriate habitat in Baca County has been lost to agriculture, and if this trend continues, populations in this area will become threatened.

Sex ratios appear to be significantly skewed from a 1:1 ratio, and Chad Montgomery's Master's thesis will address the potential reasons for this bias. No gravid female Texas horned lizards were observed, but on 30 August 1996, 10 juvenile lizards were captured in Otero County. They ranged in total length from 35-42.5 mm, and are likely neonates. It appears that hatching likely occurs at the end of August or early September, depending on weather conditions in a particular year.

In general, the Colorado populations of the Texas horned lizard have an adult size which is approximately 20-30 mm shorter than populations in Texas, Arizona and other southern states. This discrepancy has prompted Chad Montgomery to include an analysis of clinal variation of the Texas horned lizard. Presently, there are no described subspecies of the Texas horned lizard, but it is possible that this size difference has a genetic and disjunct basis, rather than occurring as a continuous clinal decrease in body size with increased latitude.

Although the present distributions of Texas and short-horned lizards in Colorado appear to be parapatric (abut, but not overlapping), the activity patterns observed may have evolved at a time when more extensive range overlap of the lizards occurred. One short-horned lizard was PIT-tagged in southcentral Las Animas County, but they do not appear to be common in this area. Part of Chad Montgomery's Master's thesis is attempting to address the relations of and reasons behind the present-day distributions of horned lizards in southeastern Colorado.

JPG -- Texas horned lizard
The Texas horned lizard (Phrynosoma cornutum) is moderately common in undisturbed shortgrass prairie habitat in both sections of the Comanche Grasslands. It is a specialist on ants, and it is rarely sympatric with the shorthorned lizard (Phrynosoma douglassii), which is common throughout much of Colorado except the extreme south eastern region where the Texas horned lizard occurs.

Massasauga rattlesnake (Sistrurus catenatus)

Only one specimen of the massasauga has been found on the Grasslands over the three years of the survey period, and this road-killed specimen was collected in the northern section in Otero County (UNC-MNH #886). We have generally found this species to be very uncommon south of the Arkansas River and it is documented in this area by only a handful of specimens. In 1996 we obtained a county record for Prowers County, and in 1997 we found what may be a small population of massasaugas in Baca County. The last massasauga record for Baca County was in 1882 (A.E. Beardsley; no specific locality given), and these new records indicate that this snake is/was more broadly distributed in southeastern Colorado than previously recognized. It is likely present in small numbers across portions of the Grasslands with appropriate shortgrass/mixed shortgrass-tallgrass habitat which have not been disturbed extensively by cultivation or overgrazing, but it is likely threatened in all areas south of the Arkansas River in Colorado. There are several robust populations north of the Arkansas, but these appear to be localized and therefore sensitive to localized habitat changes and disturbances.

In fall of 1996, we obtained seven recaptures of PIT-tagged snakes. Although none of these were from the Grasslands, they do provide information on this species and several points from the recaptures will be further discussed. The longest recapture interval was 343 days and the shortest was 11 days (mean of x = 152 days); all but one were recaptured more than 130 days after initial capture. Most snakes showed positive weight and length gains, and one snake, captured 24 April 1996 and then again on 21 September 1996, showed a weight gain of greater than 100%! Massasaugas in Colorado, though of diminutive adult size, have the capacity for (very) rapid growth. Based on rattle number, snakes appear to shed once or twice a season as adults. Two snakes showed negative weight changes over the recapture interval (-1.6 and -0.8 grams). Both of these were post-parturient females, having given birth between approximately 25 August-10 September 1996. Post-parturient females are very apparent upon inspection, as the posterior one-third is extremely flattened, muscle tone is poor, mass is low and snakes appear overall to be somewhat stressed. In contrast, one recaptured female of approximately the same size increased in weight by 25% from 24 April to 5 September 1996. These post-parturient females had approximately 30-40 days to feed and recover body weight, and given the potential for growth, in non-drought years sufficient recovery of the post-parturient females is expected. However, if they entered hibernacula in poor condition, overwinter mortality becomes much more likely (Hirth, 1966).

Radiotelemetry of massasaugas

Radiotelemetry was not conducted on massasaugas within the Comanche National Grasslands because massasaugas are quite rare in this part of the state; however, a brief account of work conducted with a robust population in Lincoln Co. is included, since basic habits are probably similar for all Colorado massasaugas. Radios (1.6 g: Holohil, Ltd. or 3.5 g: AVM, Inc.) were surgically implanted in the spring and summer of 1997 using the method of Reinert and Cundall (1982). Radios are placed in the posterior 1/3 of the body cavity and do not interfere with normal movement, feeding, etc. A total of 8 snakes were implanted; of these, only one radio lasted the entire season (lifetimes were rated at 14-26 weeks but varied from 5-35 weeks). Several snakes were recovered as the radios were about to fail, and two snakes were not recovered. However, in spite of the difficulties encountered with the radios (which are typical, particularly with smaller units), habitat utilization, movement, surface activity, duration of surface movements, seasonal movements and hibernation site location were obtained. Daily movements during summer months ranged from 1-400 meters (400 m is equivalent to ~1200 body lengths), and one snake moved >1 km within one week. Sand sage is important as a site of cover for diurnal basking, and surface activity continued through the driest months of the summer. At present, we have recorded movements as late as 21 November, and it is likely that snakes are active throughout the year as local temperature permits. Massasaugas in Colorado utilize rodent burrows in hard packed soils as hibernacula, and they appear to hibernate individually. We hope to continue this work in 1998, as the site of this population is ideal for long-term studies and our surgical and field techniques have been perfected.

JPG -- Massasauga rattlesnake
Massasauga rattlesnake (Sistrurus catenatus edwardsi). Massasaugas are uncommon on the Grasslands, but are more frequently encountered further north. However, a new population we discovered in Baca County suggests that massasaugas may still be present in areas which have not been overly disturbed. Maximum adult length in Colorado is approximately 525 mm.

Notable observations on other species of amphibians and reptiles

County distribution records for amphibian and reptile species

All state and county records are published in Herpetological Review (see Reference section), as this journal is widely available to the scientific community. With fossorial, sedentary and/or secretive species such as amphibians and reptiles, distributional information can be highly dependent on yearly variations in climate, particularly in areas poorly sampled. Publication of distribution records allows for broad distribution of this information and a better understanding of the extent of occurrence of these species.

In 1997 we added one state distributional record, six county distributional records and five significant range extensions. The Texas horned lizard was documented in extreme eastern Pueblo County and the short-horned lizard was found in Kiowa County. Four massasaugas were found in Baca County in habitat which is very reminiscent of the best habitat for massasaugas in Colorado (north of the Arkansas). The occurrence of the common kingsnake (Lampropeltis getulus) was documented for Bent County, indicating that this snake likely occurs over much of southeastern Colorado south of the Arkansas River (including on the Grasslands). A DOR Texas ratsnake (Elaphe obsoletus lindheimeri) was found in Kiowa County, but it is uncertain if this record represents a natural occurrence.

In 1996 eleven county distributional records were obtained (Appendix 5; eleven species and eight counties), and one of these (blacknecked garter snake: Thamnophis cyrtopsis) was found within the boundaries of the Grasslands. Several of these are particularly noteworthy. Two specimens of the Great Plains narrowmouth toad were found (following calls) in a deep permanent pool along an unnamed creek just south of Carrizo Creek in Las Animas County (just outside the Grasslands). Few records exist for this species in Colorado, but it probably occurs in similar appropriate habitat in many parts of southern Baca and Las Animas Counties. Specimens of the common kingsnake (Lampropeltis getulus) were found in Otero and Las Animas Counties. The Otero population, occurring along the Arkansas River drainage, now appears to be a native population, and the new record from Las Animas County, from a very remote location, indicates that the common kingsnake is likely widespread in extreme southeastern Colorado. This snake is usually common in areas in which it occurs (pers. obs.), and it may turn out to be more abundant in Colorado as further work is done in the more remote areas of the state. It also occurs in New Mexico, but it has not been recorded closer than about fifty miles south of the Colorado/New Mexico border (Degenhardt et al., 1996). A road-killed specimen of the desert massasauga (Sistrurus catenatus edwardsii) was found in Prowers County just north of the Prowers/Baca Counties line. This represents the furthest southeastern distributional record in Colorado (with the exception of the lost specimen from Baca County recorded by Beardsley in 1882).

In 1995, new county distribution records were obtained for eight species of frogs, lizards and snakes and nine counties in southeastern Colorado. Live specimens were photographed and released at the site of capture, and road-killed specimens were entered into the UNC-MNH Herpetology Collection. One of these was a road-killed massasauga, found in El Paso county. Another specimen was recently reported from this county (Pegler et al, 1995), but this report was based on a specimen obtained in 1988. Our specimen indicates that the massasauga is still found in El Paso Co. A specimen of the chorus frog (Pseudacris triseriata) was found in Kiowa Co.; several other specimens of the chorus frog were also found in southeastern Lincoln Co.

Other Non-listed but Potentially Sensitive Species

Collared lizard (Crotaphytus collaris)

Collared lizards were observed in Baca and Otero counties on a regular but uncommon basis. These predatory lizards were probably once quite common in all lower elevation areas in southeastern Colorado with extensive rocky outcrops. However, they are commonly sought after for the pet trade, and their numbers are likely on the decline. A total of 11 adult collared lizards were observed during the 1995 season. Only 6 collared lizards were observed in 1996, and this decrease is likely a sampling bias rather than an indication of further decline. However, collared lizards do appear to be less common in areas such as Vogel Canyon, where human visitation is frequent, so they may be suffering decline due to human activities.

JPG -- Juvenile collared lizard
This juvenile collared lizard (Crotaphytus collaris) was found in Vogel Canyon (Comanche Grassland, northern section). Juveniles are more brightly patterned than adults. This highly predatory lizard is likely threatened in many parts of its Colorado range because it is a large predator (therefore less common), highly visible, largely limited to rock outcrops and is frequently collected for the pet trade.

Checkered Whiptail (Cnemidophorus tesselatus)

This large, unusual and parthenogenetic whiptail lizard is generally found south of the Arkansas River in Colorado, and they are known to occur on both sections of the Grasslands. We have found them to be moderately common in the Vogel Canyon area, particularly just south of the picnic area in juniper/mixed grasses. This is a biologically interesting species which appears to have originated from hybridization between two species of whiptails, and males are essentially absent from most populations. Because it is common in areas of higher human traffic (Vogel Canyon), populations should be monitored to ensure that they do not become locally extirpated.

JPG -- Checkered whiptail
Checkered whiptail (Cnemidophorus tesselatus). This parthenogenetic species has resulted from hybridization of two other species of Cnemidophorus. Checkered whiptails appear to occur along drainages of the Arkansas River system at lower elevation, particularly along the Purgatoire River; they are moderately common in the northern section of the Grasslands, particularly near Vogel Canyon.

Prairie rattlesnake (Crotalus viridis viridis)

Prairie rattlesnakes were encountered frequently on both sections of the Grasslands but they appear to be more abundant on the southern section. However, this species is usually killed on sight, and due to continued persecution, their numbers are likely decreasing. A rancher (Cheyenne County) mentioned that in the last thirty years, he has seen only six prairie rattlesnakes. These snakes often associate with prairie dog towns, using the burrows for shelter, and as the dog towns are eliminated, rattlesnake populations will be negatively affected as well. This species appears to be generally more tolerant of habitat disturbance than many species, but because populations may den communally and thus be subject to eradication in a single season, populations on the Grasslands should be monitored for significant changes in number.

JPG -- Prairie rattlesnake
Prairie rattlesnake (Crotalus viridis viridis). This large male (>1000 mm) was found crossing Highway 160, which runs through the southern section of the Grasslands. Prairie rattlesnakes are commonly encountered on both sections of the Grasslands in most habitats. Note the typical defensive posture, with the head and forebody raised; snakes often retreat in this posture.

Green toad (Bufo debilis)

Only three specimens of the green toad were encountered from fall 1994 through 1996, and all were found in the immediate vicinity of a stock pond just east of Rourke Road and approximately 1 mile north of David Canyon Road on the Comanche Grasslands northern section (Otero County). One juvenile specimen was found in fall of 1994, and 2 additional specimens were found in early September 1996 (one by Lauren J. Livo). Other specimens have been reported from Alkali Arroyo (Jerry Kline, pers. comm.), but we have not observed them there. This species is in decline in a large number of areas of prairie where it was formerly abundant (see Collins, 1993), and it is likely in decline in Colorado as well. In 1997, heavy rains in July and August resulted in significant surface activity by this species, and it was encountered several times in Otero County. At one pond in Otero County on the northern section of the Comanche National Grasslands, at least 20 adults were observed in a breeding group. It is likely that this species is usually surface active for only brief periods following rainstorms, and this habit makes it difficult to evaluate the true status of populations. Nevertheless, it is recommended that this species be considered a species of concern, and field work focussed specifically on this species is recommended.

JPG -- Green toad
Green toad (Bufo debilis insidior). This small member of the true toad family was once broadly distributed across the southern plains, but it appears to be decreasing in numbers. However, it is highly dependent on specific moisture conditions for activity, and above-ground movements are very limited during dry periods.

Bullfrog (Rana catesbeiana)

Bullfrogs are not native to Colorado but have been intentionally introduced in numerous locations. These large, aggressive and highly competitive predators are increasing in numbers and abundance, and it is expected that concomitant with bullfrog increases will be a decrease in leopard frog (Rana pipiens and R.. blairi) numbers and populations. We have observed direct predation by bullfrogs on plains leopard frogs and on plains garter snakes (Thamnophis radix), and I currently have an Honors Thesis student (Theresa Childers) working on the effects of bullfrogs on other species in southeastern Colorado. Bullfrogs are established in all areas of appropriate habitat (semi-permanent body of water) within the Comanche National Grasslands (both sections), and they are particularly abundant along portions of the creeks in Carrizo and Cottonwood Canyons. Stock ponds, widely scattered across the plains, also provide suitable habitat and likely facilitate dispersal of bullfrogs during rainy periods. In California, bullfrogs have contributed to the local extinction of many populations of native ranid frogs, so it appears likely that the same could occur in Colorado. During a removal campaign in Ventura County, California, Dr. Samuel Sweet of UC Santa Barbara recorded a bat and a garter snake among the gut contents of bullfrogs (pers. comm.). Smaller vertebrates of all classes are potential prey of this frog, and other species of amphibians and reptiles in southeastern Colorado are therefore likely at risk. In Lincoln Co., we have observed that at all locations where leopard frogs are found, bullfrogs also now occur, and this pattern is likely for most of southeastern Colorado. Based on the several years I have been surveying the herpetofauna of southeastern Colorado, it is my opinion that bullfrog populations are on the increase. It is strongly recommended that some severe measure to remove bullfrogs without harming native ranid frogs, such as shootouts and/or providing a bounty, be commenced as soon as possible.

JPG -- Bullfrog
The bullfrog (Rana catesbeiana) has been widely introduced in eastern Colorado, and it appears to be displacing native ranid frogs as well as other smaller animals associated with ponds and larger water sources. It is a voracious predator and we have found remains of plains leopard frogs and plains garter snakes during gut content studies of bullfrogs. Vigorous immediate control of this species is warranted.

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