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Individual study: Video surveillance to assess wildlife highway underpass use by elk Cervus elaphus along State Route 260 highway, Arizona, USA

Published source details

Dodd N.I., Gagnon J.W., Manzo A. I. & Schweinsburg R.E. (2006) Video surveillance to assess highway underpass use by elk in Arizona. Journal of Wildlife Management, 71, 637-645


In response to ecological and safety issues, transportation agencies are designing structures to promote wildlife permeability across highways, particularly large bridges for the passage of multiple species. The study set out to evaluate the application of video surveillance to assess and compare differences in elk use (passage rate), probability of use and behavioural response to design characteristics at two underpasses.

Study sites: Integrated video surveillance systems were installed at two completed bridged underpasses (east underpass and west underpass) along the State Route 260 highway (34º16.9'N, 111º8.9'W) Arizona, southwest USA. Both underpasses (<250 m apart) open up into the same riparian-meadow complex. Though both underpasses were of a similar open-span bridge construction and length (41.1 m), the below-span characteristics and dimensions were markedly different:

East underpass: The east underpass was 6.8 m high, 9.6 m wide and 52.7 m in length; openness ratio 12.3; more open, natural (2:1 sloped vegetated earthen sides) sides.

West underpass: The west underpass was 11.5 m high, 16 m wide and 110.6 m in length; openness ratio 5.5; concrete, mechanically stabilised earth walls (6.4 m high).

Monitoring: The video surveillance system comprised of four video cameras. Infrared illuminators were used to illuminate the monitored area, with photo-beam triggers to detect approaching and crossing animals. These camera systems operated from September 2002 to September 2005.

Elk passage:A total of 3,708 elk in 1,266 groups were recorded at the two underpasses, with elk individuals accounting for 91% of all mammals observed using them. Nearly three times the number of elk groups were recorded at the east underpass (663) compared with the west underpass (242), with elk showing a preference for crossing at the east underpass (75% probability of use) compared to the west (66% probability of use). The highest frequency of crossing occurred on days with lowest traffic volumes.

Under pass design: The reconstruction of the State Route 260 highway evolved into a very effective adaptive management project, in which the results of this study had applications elsewhere along the highway (another 11 underpasses are planned). The Arizona Department of Transportation eliminated the concrete walls and increased floor width from 16 m to 32 m. Structural modification of the west underpass to increase wildlife usage was completed in 2006.

Conclusions: It was found that elk use was dependent upon underpass characteristics. The relative openness of the east underpass was over twice that of the west underpass, where elk had to traverse more than two times the length of the east underpass to traverse the highway. In addition to underpass length, it is believed that the concrete walls of the west underpass had a negative influence on the probability of elk crossing and higher proportion of resistant behaviours compared to the more favoured east underpass.

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