Amphibians and Reptiles of Sonoita Creek State Natural Area, Arizona

Tucson, Arizona, USA. dturner@theriver.comSonoita Creek State Natural Area of southernArizona lies in the “sky island” archipelago ofsouthwestern North America, which is known for itsrich biodiversity. Mountain ranges in the regioncontain unique biotic assemblages, with distributionaledges, gaps, and outliers that lead to a variety offascinating biogeographic questions (Warshall 1995).The valleys provide corridors between montanepopulations and allow extensions of distribution forlower-elevation species. Lowlands are generally thebest-watered, most productive parts of the landscape,and have also been the most heavily affected byhuman use, both globally and locally.The Sonoita Creek valley has been haphazardlyvisited by herpetologists for decades, but mostcollecting has been done along the main road,Highway 82, due to constraints of access to privateproperty.This inventory was a volunteer effort. The goalswere to provide qualitative information about theherpetofauna of Sonoita Creek State Natural Area,particularly species presence, but also to provideinformation on species distribution and abundance.Study areaSonoita Creek State Natural Area (SCSNA)extends east along Sonoita Creek for 7 miles from itsconfluence with the Santa Cruz River about 8 milesnorth of Nogales, Arizona, and includes lands northfrom the creek up to 5 miles (Fig. 1). It is managed bythe Arizona State Parks Department (ASP) for thebenefit of its natural values. With the initial purchase in1994, it was the first such natural area acquired withfunds from the state lottery that were dedicated in the1990 Heritage Initiative to protect “parcels of land orwater that contain examples of unique natural terrestrialor aquatic ecosystems, rare species of plants and animals,or outstanding geologic or hydrologic features.”The Natural Area has been greatly expanded withadjacent land around Coal Mine Spring, purchased in2005 and 2006 by Arizona Game and Fish Department(AGFD; also using Heritage Fund money) and US Fishand Wildlife Service but jointly managed by ASP. Whenthe areas are considered together, the Natural Areacomprises about 8,786 acres. It ranges in elevation from3,440 ft at the downstream end up to 5,466 ft in theGrosvenor Hills.For purposes of this study, I included SCSNA, theadjacent Patagonia Lake State Park, and out to one milebeyond the SCSNA boundaries.The portion of SCSNA that receives most attentionis the cottonwood/willow gallery forest along SonoitaCreek, along with associated mesquite bosques. Asidefrom the perennial flow in Sonoita Creek, the areaincludes intermittent stream reaches in Fresno and CoalMine canyons, and theperennial Coal Mine Spring.The entire area drains intoSonoita Creek. The uplandvegetation of SCSNA isprimarily semidesert grassland,with small areas of oaksavanna. A detailed flora ofthe original Natural Area,comprising 4,900 acres beforethe AGFD additions, found525 native plant species and36 exotic species (McLaughlin2006).An abandoned railroadbed along the Sonoita Creekhas been converted to a non-motorized trail, and providesthe primary access along thecreek. Prior to acquisition byASP, the area was used primarily for cattle grazing, andcattle remain a strong influence on the landscape. Othercurrent uses include trespass off-road vehicle, horse, andfoot travel along the creek bed and trail. Unlike manyplaces near the U.S./Mexico border, illegal immigranttraffic did not appear to have a strong impact duringsummer 2006.