Counting Rats from Space

The Nature Conservancy is working with partners to count and map rats using satellite technology.

Satellite Imagery of Giant Kangaroo Rat Populations

Each dot represents one "precinct" or home. Because the rats live alone, each dot also represents one rat.

“The giant kangaroo rat is the ecosystem engineer of the Carrizo Plain... [it] provides the conditions necessary to support a full suite of endangered species,”

Scott Butterfield, the Conservancy’s Central Coast ecologist

The Nature Conservancy is working with University of California Berkeley researchers and partners at Carrizo Plain National Monument to count and map giant kangaroo rat populations using satellite remote sensing data.

Giant kangaroo rats are the keystone species of Carrizo Plain. A keystone species is like the centerstone in an arch — even though it’s one small stone, it keeps the whole thing standing up.

And when a keystone species is in trouble, the rest of the ecosystem soon will be, too.

That’s why keeping track of this endangered rodent is so critical. Scientists and resource managers base important land management decisions on the size and distribution of each year’s kangaroo rat population, says Conservancy ecologist Scott Butterfield.

Nature’s Lawnmower

The giant kangaroo rat, found only in Central California, is nature’s lawnmower, clipping the grass and creating the preferred low-profile habitat — short, low-to-the-ground plants — of other endangered San Joaquin Valley species, including the kit fox, blunt-nosed leopard lizard and antelope squirrel.

About the size of an orange with a tail twice as long as its body, kangaroo rats clip the grasses around their many-roomed burrows or “precincts.”

They then pile up the grass clippings in neat, near-perfect circles at the entrance of their burrow, waiting for the grass seeds to cure in the sun before storing them.

A benefit of these mini-compost piles of clippings is an enriched soil. Plants, particularly the California jewelflower, can be three to five times more productive when growing where the stacks have been.

As Butterfield says, “The giant kangaroo rat is the ecosystem engineer of the Carrizo Plain, clipping the grass, creating the burrows and enriching the soil that provides the conditions necessary to support a full suite of endangered species.”

Counting Giant Kangaroo Rats – the Hard Way

In the past, the Bureau of Land Management tried estimating the kangaroo rat population by trapping them across the Carrizo Plain. This proved too expensive, time consuming and difficult to accomplish each year across their 150,000-acre habitat.

Next, the Department of Fish and Game tried estimating the extent of giant kangaroo rats across the Carrizo Plain by conducting aerial surveys. Most years it’s easy to spot a giant kangaroo rat precinct, even from the air, by the almost perfect circles they create while clipping.

But this approach also had its shortcomings.

“While these efforts produced important information about population distribution, the resulting hand drawn maps were not precise enough to allow annual management decisions to be made,” says Butterfield.

When there’s a lot of grass and not a lot of kangaroo rats, managers must decide whether to bring in cattle for grazing or do a prescribed burn in order to achieve the low-profile habitat that the rats maintain.

“Plus," continues Butterfield, "the process was too dependent upon the skills of each surveyor — making it nearly impossible to accurately repeat the process year after year.”

Satellite Data Makes It Faster, Better

Enter satellite remote sensing data. Butterfield says using satellite imagery allows giant kangaroo rat precincts and their population extent to be mapped accurately across the Carrizo Plain each year in a precise, quantifiable, repeatable, fast and cost-efficient way.

To map kangaroo rat precincts, images are taken in spring before the kangaroo rats begin clipping and again in summer when their work is done and their grass piles are complete.

Butterfield says that by using satellite remote sensing data scientists can more accurately predict the distribution of kangaroo rats and increase our understanding of the crucial role they play in their environment.

This information is of paramount importance as we try to understand what impact climate change might have on the environment.

“We can begin to track their response to change," says Butterfield. "If the giant kangaroo rats begin to have trouble, other species will, too. This data will help us know more about the effects that climate change might have to other threatened and endangered species at the Carrizo Plain.”


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