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Characteristics of elk-vehicle collisions and comparison to GPS-determined highway crossing patterns

  • Author(s): Dodd, Norris L.
  • Gagnon, Jeffrey W.
  • Boe, Susan
  • Schweinsburg, Raymond E.
  • et al.
Abstract

We assessed spatial and temporal patterns of elk (Cervus elaphus nelsoni) collisions with vehicles from 1994-2004 (n = 456) along a 30-km stretch of highway in central Arizona, currently being reconstructed in five sections with 11 wildlife underpasses, 6 bridges, and associated ungulate-proof fencing. We used Global Positioning System (GPS) telemetry to assess spatial and temporal patterns of elk highway crossings and compare to elk-vehicle collision (EVC) patterns. Annual EVC were related to traffic volume and elk population levels (r2 = 0.750). EVC occurred in a non-random pattern. Mean before-construction EVC (4.5/year) were lower than EVC on sections under construction (12.4 EVC/year). On the only completed section, EVC did not differ among before-, during-, and after-construction classes, even though mean traffic volume increased 67 percent from before- to after-construction levels, pointing to the benefit of three passage structures and fencing. On one section under construction, EVC increased 2.5x when fencing associated with seven passage structures was incomplete; EVC dropped dramatically once fencing was completed. We accrued 101,506 fixes from 33 elk (25 females, 8 males) fitted with GPS collars May 2002-April 2004. Elk crossed the highway 3,057 times (mean = 92.6/elk) in a non-random pattern. We compared EVC and crossings at five scales; the strongest relationship was at the highway section scale (r2 = 0.942). Strength of the relationship and management utility were optimized at the 1.0-km scale (r2 = 0.701). EVC frequency was associated with proximity to riparian-meadow habitats adjacent to the highway at the section (r2 = 0.962) and 1.0 km (r2 = 0.596) scales. Though both fall EVC and crossings exceeded expected levels, the proportion of EVC in September-November (49%) exceeded the proportion of crossings and coincided with the breeding season, migration of elk from summer, and high use of riparian-meadow habitats adjacent to the highway. The proportion of EVC and crossings by day did not differ; both reflected avoidance of crossing the highway during periods of highest traffic volume. Though traffic volume was highest from Thursday-Saturday, the proportion of EVC was below expected. A higher proportion of EVC (59%) occurred relative to crossings (33%) in the evening hours (17:00-23:00); 34 percent of EVC occurred within a one-hour departure of sunset, and 55.5 percent within a two-hour departure. EVC data are valuable in developing strategies to maintain permeability and increase highway safety including selecting locations of passage structures.

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