Overview
For the last thirty years, there has been minimal research conducted on the herpetological communities in the Las Vegas Wash (Wash). For this reason, the Las Vegas Wash Project Coordination Team (Wash Team) conducted a reptile monitoring program from May of 2001 to September 2003. The goals for the program were to determine the presence or absence of reptiles near the Wash and to gather general information on their distribution within the Wetlands Park.

Survey Location | Survey Methods

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Survey Location
Reptile array sites were located on the north side of the of the Wash channel within the Clark County Wetlands Park (Wetlands Park) boundary. When the study was initiated, a total of  six site locations were chosen according to habitat suitability in the Wetlands Park, avoiding archeological sites and planned Wash improvement areas. Sampling locations were further selected based on road accessibility. Habitat adjacent to each of the reptile array sites was moderately disturbed due to off-highway vehicle (OHV) traffic. Four site locations were added in the third year of the study, including two locations in revegetation sites and two in tamarisk dominated areas. 

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A basic habitat description for the array sites is described below.

Array Site 1
Dominated primarily by creosote (Larrea tridentata) and white bursage (Ambrosia dumosa), associated Mojave Desert scrub species included on this site are ratany (Krameria erecta), desert senna (Senna armata), ephedra (Ephedra sp.), and big galleta (Pleuraphis [Hilaria] rigida). The slopes are generally low, vegetation is sparsely clumped and the substrate is silty sand with pebbles and gravels. This array is the most distant site from the Wash and is surrounded by OHV roads.

Array Site 1

Array Site 2
Dominated by fourwing saltbush (Atriplex canescens) with infringement from honey mesquite (Prosopis glandulosa), shadscale (Atriplex confertifolia), and non-native tamarisk (Tamarix spp.), this site is characterized by steep hills with variable slopes and is within 300 feet of the Wash. OHV roads are in the vicinity of the site.

Array Site 3
Located within a silty sand flat wash that receives periodic flooding indicated by the mudcracks near the site, this array is also dominated by fourwing saltbush, with creosote, white bursage and tamarisk also associated components of this habitat. Telephone Line Road/Hollywood bisects Array Site 4 on the south and Array Site 3 on the north.

Array Site 3

Array Site 4
This site is dominated by dense thickets of fourwing saltbush with interspersed catclaw (Acacia greggii) and tamarisk.

Array Site 5
Dominated by non-native Russian thistle (Salsola tragus) and fourwing saltbush, the soils are predominately fine grained sandy silts and there is a large percentage of downed debris near the site. OHV roads are readily apparent next to this site.

Array Site 6
Robust tamarisk trees and large quailbush (Atriplex lentiformis) bushes dominate this site. The south side of this site is in a riparian buffer adjacent to the Wash that is perched 50 feet above the Wash channel.

Array Site 7
This site is located within an area that was cleared of non-native tamarisk and revegetated with native riparian and desert wash taxa, including cottonwood (Populus fremontii), Goodding willow (Salix gooddingii), sandbar willow (S. exigua), as well as honey and screwbean mesquite (S. pubescens), desert willow (Chilopsis linearis) and quailbush.  The site was planted in February 2002.

Array Site 8
This site is dominated by mature tamarisk with some large quailbush.   

Array Site 9
This site is located within a revegetation site that was planted with similar vegetation to Array Site 7.  The site was planted in November 2001.

Array Site 10
Mature tamarisk trees dominate this site, creating a thick canopy overhead.

 

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Survey Methods
Since the reptile trapping season in the Wash is best from early spring to early fall, Wash Team biologists commenced surveys in the early spring. Traps were opened for three nights at a time every other week of the trapping season. The traps were opened on a Tuesday evening and checked for reptiles on Wednesday, Thursday, and Friday mornings.

Drift Fence Array

There are many types of methodologies that biologists can use to capture reptiles. A popular technique that is used in southern Nevada, and the technique that Wash Team biologists are using, is the drift fence array. This methodology incorporates two different types of traps (the pitfall trap and the funnel trap) with each trap targeting different reptiles. The concept behind the drift fence array is that a reptile moving randomly in its habitat may move in the direction of a drift fence array and it will be obstructed by the fine mesh fabric of the fence and will "drift" towards one of the pitfall or funnel traps. There are three components of a drift fence array, the drift fence, the pitfall trap, and the funnel trap.

The Drift Fence
The first component of the drift fence array is the drift fence. The drift fences are made of a fine mesh fabric 1.5 feet in height by 50 feet long. A total of three drift fences are installed in a "Y" like configuration per array. The drift fences are fastened to wooden stakes for stability and structure and approximately 0.5 feet (of the 1.5-foot side) of the drift fence is buried underground.

Drift Fences

The Pitfall Trap
At the center of the drift fence array and at the middle and end of each drift fence is a pitfall trap (a total of 7 per drift fence array). The pitfall traps bisect the drift fences at the middle point so that a reptile may be captured if it comes into the drift array from any angle.

The Pitfall Trap

The pitfall trap is a 6-gallon bucket that is buried in the ground so that the lip of the bucket is flush with the ground surface. It is important to have a bucket deep enough to detain a reptile that may otherwise be able to get out. The bucket lid of the pitfall trap is modified with three wooden feet attached to its top. When pitfall traps are "opened," the modified lid is inverted over the bucket and secured with bungee chords from within the bucket. This configuration creates shade in the pitfall trap.

Secure Pitfall Trap

When pitfall traps are "closed," the lid is securely fastened to the bucket to prohibit a reptile capture. This type of trap is usually more effective for capturing lizards than snakes. Small lengths of PVC piping are placed in the pitfall traps to create cover for reptiles that are detained.

The Funnel Trap
There is only one funnel trap for each drift fence arm (a total of 3 per drift fence array). Each funnel trap is located three-quarters of the distance from the drift fence center and only on one side of the drift fence.

Modified Funnel Trap Lid

The funnel trap consists of a modified lid and a 6-gallon bucket that is buried in the ground so that the lip of the bucket is flush with the ground surface. A mesh wire cloth cylinder with funnels on either side is attached to the lid. Within the cylinder, there is PVC piping in the shape of a "T." One end of the "T" shaped PVC piping protrudes through the bucket lid. When the lid is securely fastened to the bucket, the PVC piping acts as a funnel into the bucket.

The funnel trap is completed by angling a piece of plywood over the funnel trap lid when it is secured to the bucket. This creates shade in the event that the captured reptiles stay within the cylinder and do not funnel into the bucket. Small lengths of PVC piping are also placed in the funnel traps to create cover for reptiles that are detained. When the funnel traps are "closed," an unmodified lid secures the opening of the funnel trap.
    

Funnel Trap Configuration

Because reptiles can not produce internal body heat (ectothermy) they are subject to external heat sources to maintain their body temperature. Creating shade over the pitfall and funnel traps increases the survival rates of captured reptiles because it reduces their exposure to the sun. Wash Team biologists also check traps in the early morning to reduce the amount of time a reptile may be subject to the intense heat of the sun.

When a reptile is found in a pitfall or funnel trap, it is weighed and measured for length; examined for age, sex, and the presence of parasites; and marked by toe clipping (lizards only). Wash Team biologists use the toe clipping methodology, which utilizes a systematic numbering system to uniquely identify each lizard, in order to estimate the relative abundance of lizard populations near the Wash.

Toe Clipping Numbering System	Toe Clipping a Desert Horned Lizard

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