Mapping Central Valley Bird Habitats

Mapping Central Valley Bird Habitats with Aerial Laser Surveys

Researcher:

Nathaniel E. Seavy
CALFED Postdoctoral Research Fellow
PRBO Conservation Science
Petaluma, CA
E.: nseavy@prbo.org
T.: (415) 868-0655 ext 311

Relevant Links:

Tools:

Revised:

March 4, 2008

Image courtesy of Chris Aldridge

March 4, 2008

Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334

In the hopes of encouraging a greater level of bird conservation in the Central Valley, a CALFED Fellow has developed a new tool for identifying habitat areas for 10 common riparian bird species.

The tool is based on a laser technology known as LiDAR, short for light detection and ranging, usually used to map the topography of earth. LiDAR can also be used to map the topography of vegetation – that is, the canopy heights. The project’s core discovery is that plant elevation data are relatively good indicators of where different species of birds can be found.

“We can predict where the birds will be with the remote sensing technology over areas impossibly large to survey by foot,” said CALFED Fellow Nat Seavy, an ornithologist with PRBO Conservation Science and UC Davis, explaining the project’s significance.

According to his analysis, six riparian bird species – the black-headed grosbeak, oak titmouse, ash-throated flycatcher, house wren, spotted towhee and Bullock’s oriole – live in areas where the canopy height is greater than 5 meters, in other words in the cottonwood forests that line the Cosumnes River Preserve, the study site, located in southeastern Sacramento County.

The red-winged blackbird, in contrast, was found in open areas, where the LiDAR measurements indicated a relatively low canopy height. Other species, such as the bushtit, song sparrow and wrentit were observed in areas with intermediate canopy height or complex vegetative structure, which may include young trees, various willows, blackberry and rose bushes, grasses and sedges.

“Our results are very obvious for anyone who knows about birds,” Seavy said. “What is not obvious is that we could use LiDAR to map habitats for so many species.”

Dusky flycatcher with brown-headed cowbird nestling. Photo: Chris McCreedy

LiDAR uses a laser to measure the distance from the aircraft, on which the instrument is mounted, to the ground below. Some of the emitted laser beams also bounce off plants. The military, the original end-user of the technology, filtered out this signal as noise since it was interested in mapping only the hard terrain, to identify things like tank routes and landing strips, explained Jim Quinn, co-director of the Information Center for the Environment at UC Davis and Seavy's current academic mentor. The plants were in the way.

The technological crux of the project has been to use this “noise” to reconstruct the canopy heights of vegetation, explained Seavy’s collaborator Joshua Viers, also at UC Davis. Seavy’s task has been to correlate field data on where birds are living, collected in 2004 and 2005 by PRBO researchers, with the LiDAR plant elevation data.

LiDAR does not give direct information on the plant species (whether they are native or non-native, for example) or on the structure of understory vegetation, on which some species rely. Because of these limitations, CALFED community mentor Chrissy Howell, an ornithologist at PRBO whose expertise is in the state’s coastal song sparrows, said she was surprised by the ability to model bird habitats with LiDAR. “A lot of birds forage and nest in understory vegetation,” she said.

Seavy notes that he originally tried to model habitats for 16 bird species and was successful with only 10. One of those he could not model was the brown-headed cowbird, which Seavy said is well recognized as “being hard to predict.”

Despite the limitations of LiDAR modeling, Seavy believes remote sensing data can be used to improve riparian restoration projects. LiDAR is being flown for many Central Valley restoration projects, he said, citing as an example Cache Creek in Yolo County, a former gravel mining area.

LiDAR can be used to evaluate the type and amount of vegetation that should be planted to create habitats for target species, he said. It can also help managers explain the absence of certain birds.

Yet another of its strengths is that it allows scientists to examine the spatial scales that are important to maintaining healthy bird populations. The brown-headed cowbird, for example, is associated with very large-scale landscape features, beyond that measured for the project. The bird is often abundant along habitat edges associated with human encroachment, Seavy said. The 7,000-hectare Cosumnes River Preserve, in contrast, is an unusually pristine natural area.

None of the 10 bird species modeled are threatened or endangered. However, all are dramatically less abundant than they were 100 years ago. “We want to make sure that common birds stay common,” PRBO ornithologist Howell said. “There is a great relationship between song birds and habitat quality. Birds are a great way to score the success of restoration projects.”

“We can build on this study,” she said. “A next step would be to look at bird reproduction in relation to LiDAR data.”