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  • Protecting wildlife part of Santa Cruz River construction projects

    Feb 13, 2020 | Read More News
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    The Pima County Regional Flood Control District relocated hundreds of reptiles, including a rarely seen species, as part of a wildlife salvage and rescue project along the Santa Cruz River. 

    This wildlife rescue effort took place ahead of a pair of flood control projects that are currently underway to remove excess sediment from the riverbed and to construct bank protections on the northern side of the Town of Marana’s 104-acre El Rio Open Space Preserve
    In planning the projects, Jennifer Becker, District Principal Hydrologist, was aware that Marana is near the farthest eastern range of the rare and elusive desert iguana (Dipsosaurus dorsalis), and if they were present they would be at risk due to the construction activities. 

    When the District undertakes larger construction projects in key urban habitat areas, they frequently take extra precautions to minimize impact to native wildlife. So the District contracted with Harris Environmental Group and University of Arizona herpetologist Dr. Phil Rosen to conduct trapping and relocation rescue operations last fall. This was prior to lizards and snakes going into hibernation on the terrace where the sediment removal is taking place. 

    “I was positively elated to learn that we saved not one, but two desert iguanas with our trapping efforts,” stated Becker. “Iguanas are not typically found in lower elevation floodplains, which make the successful rescue effort all the more exciting.”

    Both desert iguanas were relocated to similar habitat along the Santa Cruz River within a couple of miles of where they were captured. 

    Desert iguanas are typically between four and five inches long and fairly long-lived, with some reaching up to seven years in the wild. They also have some of the highest heat tolerance of any reptile, often being most active during the late morning and early afternoon. Body temperature readings of one was recorded at 116 degrees, which is the highest known for any reptile. 

    Their habitat is associated with the presence of creosote bush (Larrea tridentata). Desert iguanas like to eat flowers from the bush during the springtime. Insects and other arthropods supplement desert iguana diets during the rest of the year. 
    In all, 546 lizards of eight different species were saved and relocated ahead of the current Santa Cruz River and El Rio Preserve project. Numbers included five Sonoran spotted whiptails (Aspidoscelis sonorae), 89 tiger whiptails (Aspidoscelis tigris), and 388 side-blotched lizards (Uta stansburiana). The UofA's Rosen was pleased to find Sonoran desert whiptails as well, and he says that their populations have been diminishing along the Santa Cruz River. 

    Construction projects can be very destructive for most lizards, but unlike many other species, they retreat underground and meet their doom due to heavy earthwork. This highlights the importance of salvaging these species prior to such projects in order to protect urban wildlife biodiversity.

    The District’s Santa Cruz River and El Rio Preserve construction work broke ground on Jan. 27. Sediment removed from the bottom of the channel will be relocated to the El Rio Preserve area south of the excavation work. 

    The excavated sediment will be used to create bird viewing islands and provide habitat for other wildlife species and native vegetation. Sediment will also be used to construct soil cement bank protection along the northern side of the Preserve to minimize the damage from frequent flooding that also brings trash and invasive species. 

    All construction activity will occur in the river bottom and the El Rio Preserve area with negligible impacts to The Chuck Huckelberry Loop and pedestrians in the area. The path will remain open for the duration of the project, which is expected to take up to three months.   

    The Pima County Regional Flood Control District has worked with local biological experts to save toads and lizards in key habitat areas prior to larger construction projects since 2004. Salvage and release sites have been monitored over time to better inform future efforts. Other notable successful projects include saving 182 regal horned lizards in 2010, and establishing new lizard and toad populations in formerly degraded urban habitat.

    One of the main benefits of wildlife trapping is that it conveys what type, and how many, of a given species exist in an area. Another benefit of wildlife trapping is the relocation of species that exist in an area that may become damaged or altered to an extent where their continued existence is in jeopardy. 

    This project epitomizes the conservation efforts of the District to help protect and save a species small in stature, but large in prominence. Continued efforts like these could help inform the role desert iguana plays in this habitat, of which very little data exist. 

    For more information regarding the desert iguana, visit the Tucson Herpetological site,  For more information regarding the El Rio Preserve Bank Protection Project, call 520-724-4600 or visit the El Rio Preserve project site