By Blake Ledbetter
For centuries, wild landscapes have been increasingly fragmented through encroachment by human development resulting in a suite of negative impacts for both wildlife and human populations. Over the past 30 years, the negative effects of wildlife presence on roadways have increased the concern among both wildlife management agencies and transportation agencies. To mitigate the negative effects (e.g. habitat and population fragmentation, animal-vehicle collisions, economic and biodiversity loss, etc.) wildlife management and transportation agencies collaborate to increase permeability on the landscape in the form of wildlife crossing structures. Wildlife crossing structures have been increasingly implemented in the United States and as research progresses, managers have slowly improved criteria for design and placement strategies to maximize the effectiveness of each crossing structure.
While wildlife crossing structures serve their purpose in creating permeability in a fragmented landscape, some are more effective than others in facilitating animal movement from one side of a barrier to the other. Measures of use and effectiveness for wildlife crossings are determined by multiple factors which ultimately guide researchers in the design and implementation of future structures depending on the management goals and target species. These criteria are typically based on the cost of the project compared to the amount of money saved as a result of the project (cost-effectiveness), if the crossing is successful in achieving the goals that were set in place with the project (typically human safety, animal welfare, and wildlife conservation), and whether animals appear to incorporate crossings frequently enough to be determined effective.
In 2018, Utah Department of Transportation installed a wildlife overpass within Parleys Canyon, crossing 6 lanes of Interstate 80; the overpass was operational in 2019. In 2020, Utah State University, under the direction of Dr. Nicki Frey, began monitoring Parleys Canyon Overpass (PCO) to determine its effectiveness as a crossing opportunity for ungulates and other wildlife species. The primary objective of the overpass was to reduce wildlife-vehicle collisions involving moose (Alces alces) and mule deer (Odocoileus hemionus). The overpass is unique in its construction, having a width: length ration of 0.13, which is much smaller than the recommended 0.80 ratio suggested by the Federal Highway Administration. The objectives of our study included: determine the crossing rates of ungulates, determine species visitation of the overpass, compare the effectiveness of the overpass to other wildlife crossing structures in Utah.
More information about wildlife crossing structures can be found at wildlifemigration.utah.gov/land-animals/crossing/
For centuries, wild landscapes have been increasingly fragmented through encroachment by human development resulting in a suite of negative impacts for both wildlife and human populations. Over the past 30 years, the negative effects of wildlife presence on roadways have increased the concern among both wildlife management agencies and transportation agencies. To mitigate the negative effects (e.g. habitat and population fragmentation, animal-vehicle collisions, economic and biodiversity loss, etc.) wildlife management and transportation agencies collaborate to increase permeability on the landscape in the form of wildlife crossing structures. Wildlife crossing structures have been increasingly implemented in the United States and as research progresses, managers have slowly improved criteria for design and placement strategies to maximize the effectiveness of each crossing structure.
While wildlife crossing structures serve their purpose in creating permeability in a fragmented landscape, some are more effective than others in facilitating animal movement from one side of a barrier to the other. Measures of use and effectiveness for wildlife crossings are determined by multiple factors which ultimately guide researchers in the design and implementation of future structures depending on the management goals and target species. These criteria are typically based on the cost of the project compared to the amount of money saved as a result of the project (cost-effectiveness), if the crossing is successful in achieving the goals that were set in place with the project (typically human safety, animal welfare, and wildlife conservation), and whether animals appear to incorporate crossings frequently enough to be determined effective.
In 2018, Utah Department of Transportation installed a wildlife overpass within Parleys Canyon, crossing 6 lanes of Interstate 80; the overpass was operational in 2019. In 2020, Utah State University, under the direction of Dr. Nicki Frey, began monitoring Parleys Canyon Overpass (PCO) to determine its effectiveness as a crossing opportunity for ungulates and other wildlife species. The primary objective of the overpass was to reduce wildlife-vehicle collisions involving moose (Alces alces) and mule deer (Odocoileus hemionus). The overpass is unique in its construction, having a width: length ration of 0.13, which is much smaller than the recommended 0.80 ratio suggested by the Federal Highway Administration. The objectives of our study included: determine the crossing rates of ungulates, determine species visitation of the overpass, compare the effectiveness of the overpass to other wildlife crossing structures in Utah.
More information about wildlife crossing structures can be found at wildlifemigration.utah.gov/land-animals/crossing/
Species Visitation
To date, there have been 4300 wildlife visits to Parleys Canyon Overpass (PCO). A visit does not indicate a crossing; rather wildlife may simply use the apron of the crossing structure, conduct activity on the structure, or effectively cross from one side of the overpass to the other. However, this number does constitute unique visits of wildlife, using the methods provided in the first section of our report. Of these, 105 entries were unidentifiable small mammal species and 11 were unidentifiable birds.
Mule deer (Odocoileus hemionus; 3071 visits), coyote (Canis latrans, 308 visits), moose (Alces alces; 135 visits) and humans (308 visits) were the most common visitors to the PCO (Figure 1). Human visitors did not include maintenance workers or our researchers. Note that mule deer were so common, that they were presented on a separate axis to display these visitations properly. Of importance, moose and mule deer, the target wildlife species of this project, were visiting the overpass within a year of construction and were the most common visitors to the structure. Also, visitation did not increase over time, suggesting that external factors such as food availability and population density may be influencing visitation rates, rather than an increased acceptance of the structure.
Mule deer (Odocoileus hemionus; 3071 visits), coyote (Canis latrans, 308 visits), moose (Alces alces; 135 visits) and humans (308 visits) were the most common visitors to the PCO (Figure 1). Human visitors did not include maintenance workers or our researchers. Note that mule deer were so common, that they were presented on a separate axis to display these visitations properly. Of importance, moose and mule deer, the target wildlife species of this project, were visiting the overpass within a year of construction and were the most common visitors to the structure. Also, visitation did not increase over time, suggesting that external factors such as food availability and population density may be influencing visitation rates, rather than an increased acceptance of the structure.
At least 34 wildlife species were identified using PCO, either to cross or simply as part of their daily activities around the structure. We counted birds that we recorded on our cameras, because their presence around the structure represents acceptance of the overpass within the environment. Four bird species were identifiable: Green-tailed towhee, dark-eyed junco, mourning dove, and black-billed magpie. Other birds were detected but unidentifiable
More Information About Crossings
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Wildlife Crossings are a complex issue. Why do we create wildlife crossing structures? How do we know where to put the wildlife crossings structures? Are wildlife crossing structures worth it? These are just a few of the terrific questions people have about wildlife crossing structures. Clink on the links below to watch a few videos about these wildlife management options.
SciLine - Scientific Expertise and Context on Deadline Recorded April 16, 2024 E330 - What is the best way for Bambi to cross the road? Driving You Crazy by Jason Luber |
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