Biology Reference
In-Depth Information
George was always keen to apply a new technology or to tinker with older versions. When
his research began four years earlier, in order to learn how many jaguars lived in this area
and how much of which habitats they used, George and his colleagues placed automatic cam-
eras known as camera traps in the dense forest to document the presence of species, such as
jaguars, that shun detection by human eyes. A camera is set up along an animal trail, and
whenever a moving subject passes in front of it, a sensor is triggered and—
Click!
—a photo-
graphic record is made, with an electronic date and time stamp. The results can be breathtak-
ing. With the use of hidden cameras, species that were once ghosts—never seen by anyone
or absent for decades—suddenly reappear.
Remote camera traps also enable estimation of actual densities of species that are almost
never seen. Biologists have adapted statistical methods to derive numbers from photographic
records of known individuals. Luckily, jaguars are perfect for this system because their spot
patterns offer unique identification for each cat. The trick, though, is to set up opposing cam-
eras to photograph each side of the passing jaguar (or other spotted or striped cat) because
the spot pattern differs on the left and right flanks. If George and his team saturated the forest
with enough camera traps placed at proper intervals and covered a sufficiently large area in a
relatively short time, they could obtain a density estimate.
Even with the cameras, however, George's question could not be fully answered. The
method depends on the area studded with cameras being larger than the home range of the
study animal. Yet George's initial camera trapping grid, an area about as large as 10,000 soc-
cer fields, proved too small to contain the entire home range of a single jaguar. In fact, one
male used an area eight times larger! At best, the camera trapping effort offered an indication
of jaguar presence.
To learn more about their daily movements, George had no alternative but to start catching
jaguars and fitting them with tracking devices so that he could map the movements of each
individual. The jaguars proved elusive. Adapting techniques from other studies, George and
his team set large live traps—baited with pigs, dogs, and chickens, each housed safely in a
separate compartment of the trap—in different parts of the forest.
Despite many attempts, these baited traps captured very few jaguars. George called in
some expert cat catchers, who suggested that recordings be played of the cats' breeding calls
and of vocalizations made by their prey. This decoy did the trick. Within a year, George and
his team had more pumas and jaguars radio-collared than had ever been accomplished before
in the Amazon.
In a region with no roads, however, tracking radio-collared jaguars on foot or by boat
turned out to be futile; even when collared animals were nearby, the dense forest swallowed
up the signals—the jaguars might as well have been a hundred kilometers away. In an air-
plane flying above the canopy, though, the signal was loud and clear, and George could loc-
ate all of his collared animals each time with a few hours of flying.
