What is a viewshed?
A viewshed refers to all the sightlines available to an individual and their spatial extents. Habitat structure (e.g., topography, vegetation) block lines of sight and changes the range at which visual information can potentially be gathered. So the viewshed is directly influenced by habitat structure.
What is Viewshed Ecology?
Viewshed Ecology is the study of how the viewsheds accessible to wildlife influence their behavior and ecology. Studies focus on how viewsheds influence spatial behavior and resource selection at a variety of scales.
Why does viewshed ecology matter?
The sensory information available to wildlife in their environments provide cues about the environment and other wildlife within it. Wildlife use these cues to make decisions about habitat and space use. To understand why wildlife select some habitat over others, we need to understand the sensory information available. Viewshed ecology focuses on visual sensory information. The viewshed accessible to wildlife can affect territory size, shape, and use, selection of breeding sites, and perceptions of predation risk.
How do viewshed ecologists figure out what animals see?
Unfortunately, we cannot measure exactly what wildlife see. Estimates of the viewshed allow us to index the area from which an animal can potentially gather visual information based on habitat structure. Traditional methods of viewshed estimation are usually two-dimensional (2D), such as taking photos of brightly colored boards and estimating how much of them is visible. However, because wildlife move through and are influenced by three-dimensional (3D) landscapes, methods of viewshed estimation are increasingly using 3D structural data. We use 3D data gathered from lidar.
what is lidar?
Lidar is a remote sensing system that uses lasers to measure physical structure. Lidar systems emit lasers that bounce off structure and time how long it takes for the light return. Because the speed of light is constant (299,792,458 m/s), the system can use the amount of time taken for the light to leave and return to calculate the distance to the structure. With measurements about the angles at which the light was emitted and returned, the system can determine the position of the structure in space. When this is done thousands of times, a 3D data "point cloud" is created that is a highly accurate depiction of measured structure. We can estimate 3D viewsheds of individuals moving through environments measured with lidar. Below are videos of point clouds gathered in a forest and a sagebrush steppe. Check out this great introduction to lidar video that was created by the National Ecological Observation Network (NEON) here.
What influences viewshed selection?
This is a big question that we ask every day! Not all wildlife select habitat that have the biggest viewsheds available. A habitat property directly related to visibility (and therefore viewsheds) is concealment - how well habitat structure blocks an animal from visual detection by others. In general, as the viewshed increases, concealment decreases so individuals manage a trade-off between these properties. Other factors may be important too. Big viewsheds are associated with less habitat structure and for some species, less forage. So individuals may have to choose sites with smaller viewsheds where danger is harder to detect because there is simply more food available. Viewshed ecology involves teasing apart these different factors to understand how the viewshed influences individuals and groups.