The National Wildlife Refuge System’s Southwest Region Inventory and Monitoring (I&M) initiative and Balcones Canyonlands National Wildlife Refuge are using airborne technology with a new level of sophistication for the benefit of endangered songbirds.


Aerial photos and satellite images long have helped the U.S. Fish and Wildlife Service determine what habitat to protect for endangered species. And limited use of light detection and ranging (LiDAR) is quite common on national wildlife refuges. But since 2012 Balcones Canyonlands Refuge and the regional I&M initiative have been using LiDAR altimetry extensively to identify patches of habitat that can best support thriving populations of endangered golden–cheeked warblers and black–capped vireos. The resulting three–dimensional “picture” is helping biologists, fire managers and other specialists see how to best protect and restore habitat for the birds.


The 25,000–acre refuge in the Hill Country of central Texas was established in 1992 to conserve habitat for warblers and vireos. Both are neotropical migrants that winter in Mexico and Central America and occupy a narrow breeding range in the southwestern United States in spring and summer. The warbler prefers older oak and Ashe juniper woodlands; the vireo prefers semi–open shrublands.


LiDAR works much like a laser rangefinder, estimating distance to an object. But a LiDAR sensor is mounted on aircraft, sends out a pulse of laser light and receives back thousands of individual measurements from objects below in the blink of an eye. Each measurement, or “return,” is mapped to create a detailed 3D sketch that can include trees, shrubs, buildings, bridges, wind turbines, telephone lines and other land features.


Highly accurate vegetation height, density and canopy cover data layers from LiDAR can augment on–the–ground field surveys to identify the songbirds’ preferred habitat. The 3D images are being used to characterize warbler habitat in particular. They depict land features with striking clarity not widely available less than a decade ago.


Helps Set Goals

“We needed a way to identify the best habitat for warblers and other endangered species, like the black–capped vireo, using scientifically credible techniques that can be repeated to monitor changes, both on and off refuge lands,” Balcones Canyonlands Refuge manager Deborah Holle says. “LiDAR is now playing a big part in that.”


I&M wildlife biologist and biometrician Sarah Lehnen agrees: “We are able to learn so much more about what type of habitat conditions really matter to breeding warblers. This information can then be used to set management goals and identify high–priority habitats.”


Older, taller trees and dense juniper and oak tree cover preferred by golden–cheeked warblers can be mapped from LiDAR data and imported into a geographic information system (GIS) or other software to model relationships between on–the–ground bird surveys and habitat conditions.


“It’s astounding how strong the relationships are when we compare our bird surveys and vegetation data to tree height and canopy cover GIS layers developed from LiDAR,” says I&M biologist Jim Mueller, who has designed a bird monitoring protocol for the refuge. “LiDAR is not necessarily replacing surveys on the ground. It’s adding value to field data by allowing us to model habitat relationships and map them to better target management activities.”


Making LiDAR work in a conservation management context at Balcones Canyonlands Refuge and elsewhere requires collaboration.


“These data don’t just roll out of the computer” says Mueller. “We’ve had to coordinate our field–sampling efforts with biometricians, remote–sensing scientists, landscape ecologists, fire managers and other I&M staff from the very beginning, working as an interdisciplinary team with different strengths and skills.”


Wildland fire is an important factor in maintaining warbler habitat. LiDAR’s ability to characterize woodland understory, overstory and hazardous fuel conditions is being explored.


Steven Sesnie is a spatial ecologist with the Refuge System’s Southwest Region Inventory and Monitoring initiative in Albuquerque.