Use of simulated highway underpass crossing structures by flat-tailed horned lizards (Phrynosoma mcallii).
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Use of simulated highway underpass crossing structures by flat-tailed horned lizards (Phrynosoma mcallii).

Filetype[PDF-694.47 KB]

  • English

  • Details:

    • Publication/ Report Number:
    • Resource Type:
    • Geographical Coverage:
    • Edition:
      Final report; June 2005-Feb. 2007.
    • NTL Classification:
      NTL-ENERGY AND ENVIRONMENT-Environment Impacts ; NTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and Structures ;
    • Abstract:
      The flat-tailed horned lizard (Phrynosoma mcallii) occupies a restricted range in the Lower Sonoran Desert of

      southwest Arizona, southeast California, and adjacent land in Mexico. Because they exhibit behavior patterns

      that include basking and remaining motionless when danger approaches, flat-tailed horned lizards are

      particularly susceptible to mortality on roads. Therefore, roads and new road construction are recognized as

      threats influencing the long-term persistence of this species. The propensity for flat-tailed horned lizards to

      use culverts as road crossing structures to avoid vehicle-caused mortality is unknown. From 2005-2006 we

      studied flat-tailed horned lizard use of a variety of simulated road crossing structures. The study objectives

      were to 1) determine if flat-tailed horned lizards will pass through culverts of sizes commonly used in road

      construction, and 2) compare and describe the characteristics of culverts used by flat-tailed horned lizards to

      those not used. We built a testing facility with six culverts of three dimensions and two interior lighting

      options. All culverts were 40 feet long; the three types included 24-inch diameter steel culverts, 36-inch

      diameter steel culverts, and 4-foot tall by 8-foot wide box culverts. One of each type of culvert was lit with

      skylights, and one of each type of culvert had only natural light from the ends. Light and temperature

      conditions in the culverts were evaluated during the study. Out of 54 flat-tailed horned lizards placed in the

      testing facility, we observed 12 complete crossings. The 36-inch diameter culvert without skylights was used

      five times. The 24-inch diameter culvert with skylights was not used, and other culvert designs were each

      used once or twice. Results indicated that flat-tailed horned lizards can use culverts as road crossing

      structures, but the evidence did not reveal a strong selection for or against any culvert type.

      Recommendations for employing appropriate road crossing structures are discussed.

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