Mule Deer Migrations and Highway Underpass Usage in California, USA

Abstract

Roadways may pose barriers to long‐distance migrators such as some ungulates. Highway underpasses mitigate wildlife‐vehicle collisions and can be an important management tool for protecting migration corridors. In northern California, 3 underpasses were built on United States Route 395 (Route 395) in Hallelujah Junction Wildlife Area (HJWA) in the 1970s for a migratory mule deer (Odocoileus hemionus) herd that had been negatively affected by highway traffic. To determine whether these underpasses were still reducing mule deer mortalities >40 years after construction, we investigated deer use of the underpasses from 2006–2019 using cameras, global positioning system (GPS) collars, and roadkill records. We used occupancy models, approximations of GPS‐collared mule deer movement paths, and roadkill locations to estimate the highway crossing patterns of deer. From camera data, there was higher use of the underpasses by deer during migration (spring [Mar–Jun], fall [Oct–Dec]) than in summer (Jul–Sep), when only resident deer were present. Higher underpass usage occurred in the spring compared to fall migrations. Eleven of 21 GPS‐collared migrating mule deer crossed Route 395. We estimated 30% of the crossings (by 7 of the 11 deer) occurred south of the underpasses where deer could easily access the highway because of short (1‐m high) and deteriorating highway fencing. Roadkill data confirmed that deer‐vehicle collisions were occurring south of the underpasses and at the underpasses. This was likely due to deteriorating infrastructure at the underpasses that allows wildlife access to the highway. Overall, our study indicated that although underpasses can provide safe passage for migratory deer decades (>40 yr) after their construction, deteriorating infrastructure such as fencing and gates can lead to wildlife mortalities on highways near underpasses. © 2021 The Wildlife Society.

Managing Landscape Urbanization and Assessing Biodiversity of Wildlife Habitats: A Study of Bobcats in San Jose, California

“…The results from these wildlife crossings have been encouraging. Monitoring studies have shown a significant decrease in wildlife-vehicle collisions in areas where these crossings are present [39]. Furthermore, they have contributed to maintaining genetic diversity within wildlife populations by allowing for greater movement and interaction among separate groups [38].…”

Fence types influence pronghorn movement responses

“…Anthropogenic barriers (henceforth, “barriers,” e.g., fences, reservoirs, and roads), coinciding with land‐use, development, and management practices, are ubiquitous and increasing worldwide, posing threats to animal movements and their ability to access resources (Jakes et al, 2018; McInturff et al, 2020; Van Moorter et al, 2020). Barriers that are impossible or difficult to cross can result in additional energy expenditure, injury, or direct mortality (e.g., drownings, fence entanglements, and vehicle collisions; Caldwell & Klip, 2021; Harrington & Conover, 2006; Rautenstrauch & Krausman, 1989; Rey et al, 2012). These effects can be exacerbated during times of abnormally severe environmental conditions, such as heavy snowfall or drought (Van Moorter et al, 2020).…”