Arizona is currently experiencing an increase in human development and a subsequent increase in roadway traffic. Man-made barriers to wildlife movement, such as roads, pose a significant threat to the long-term persistence of wildlife populations worldwide through habitat fragmentation and direct mortality (i.e., road kill). The preservation of critical wildlife linkages has become an important strategy to reduce these impacts and multiple highway connectivity projects are underway throughout the state.
The first step in maintaining habitat connectivity for Arizona’s wildlife is identifying where connectivity is threatened. At the Game and Fish Department, we use a variety of techniques to identify the most biologically meaningful location for wildlife linkages and site-specific crossing structures. While radio-telemetry techniques provide the most detailed dataset for identifying wildlife movement patterns relative to roadways, the costs of such studies can be prohibitive when placed in the context of hundreds of road construction and modification projects underway statewide.
Animal mortality locations along roadways can act as a reliable indicator of wildlife crossings areas and are particularly useful at the level of a specific roadway construction project. Often called ‘hot-spot analyses’, surveys for road killed wildlife are a cost effective technique for identifying the need for, and placement of, funnel fencing and crossing structures to reduce road kill and increase habitat connectivity. Additionally, these studies are easily replicated at multiple project areas and can be implemented before and after the installation of fencing and crossing structures to gauge their effectiveness.
Depending on the length of the road segment to be evaluated, surveyors will walk or drive the length of the segment in an effort to document the spatial locations of all road killed wildlife. It’s important to do this just after sunrise because scavengers such as ravens and coyotes are busy conducting their own surveys (i.e., breakfast!). In addition, wildlife track surveys can be used to identify patterns in wildlife movement along, or across, the roadway. The time interval between successive surveys must be determined based on the specific study objectives. In general however, road kill surveys are conducted on a weekly basis. All road kill is identified to species and their locations are recorded with the use of the GPS unit.
Graphical representations of the frequency of road kill accumulation can then be developed based on these data and used to identify road kill ‘hot-spots’. Generally, the road segment will be divided into smaller segments (often 0.10 mile segments) and the number of road kill will be tabulated for each segment. Under this methodology, more complex statistical analyses can also be performed to examine the influence of topography, habitat, and/or weather conditions on these hot-spots.
- A recently completed road kill study on US 93 identified 13 avian species, 19 mammalian species, 3 amphibian species, 15 lizard species, and 19 snake species for a total of 5,684 road killed animals along an 11 mile segment. Hot-spots were readily identified from the combined dataset of road kill locations for all species detected.
- An on-going study along a 1 mile stretch SR 87 has identified the location of 10 road killed desert tortoises.
Future Permeability Analyses
- State Route 86 (Ajo Highway): This study, sponsored by Arizona Department of Transportation, will identify road kill ‘hot-spots’ on Ajo Highway from Kinney Road to the Tohono O'odham Nation boundary.
- Tangerine Road in Pima County: This study, sponsored by the Town of Oro Valley and the Town of Marana, will identify road kill ‘hot-spots’ on Tangerine Road from Interstate 10 to La Cañada Road.
- Houghton Road in Pima County: This study, sponsored by the City of Tucson, will evaluate roadway permeability along Houghton Road from 22nd Street to Valencia Road.
The results of these ‘hot-spot’ analyses identify the need and placement of wildlife-friendly engineering designs that aid in maintaining wildlife connectivity. Implementation strategies such as land bridges and/or large box culverts will be dependant on final roadway engineering plans and the biology of the species impacted by the roadway. The efficacy of these mitigation strategies are dependant on long term commitments from public and private stakeholders involved with managing or conserving wildlife linkage zones. In addition, post-construction monitoring is an essential component of any wildlife mitigation strategy and will provide a method for gauging the success of the strategy.
For more information contact:
Shawn F. Lowery , Arizona Game and Fish Department
5000 W. Carefree Highway Phoenix, AZ 85086-5000
(520) 742-1911 Email: email@example.com