London, August 11 : A new study has enabled to reconstruct the last months of a cougar's life by analyzing the chemical isotopes in its claw, a technique that could help conservation biologists and land managers to track the movements of animals.
Cougars, like all animals, carry an invisible history of their movements in non-living tissue such as claws and hair. These contain characteristic ratios of stable isotopes, unique to a particular location and determined by the food and water they consume.
Stable isotope tracking has seen "an explosion of applications" since pioneering work on monarch butterflies in the mid 1990s.
According to a report in Nature News, Keith Hobson, an isotope ecologist at Environment Canada in Saskatoon, Saskatchewan, along with Viviane Henaux and Larkin Powell of the University of Nebraska, Lincoln, Hobson, applied the technique to the claw of a cougar that met its end on a highway near Greta, Nebraska in November 2005.
Hobson used stable isotope mass spectrometry on a powdered portion of the claw, to measure the ratio of hydrogen to deuterium; and of carbon-12 to carbon-13. As the claw grew, it recorded the ratios that were unique to each part of the state.
The team then created reference maps showing variation in the isotope ratios across Nebraska.
The maps were based on the isotope ratios found in the lymph nodes of deer shot in different parts of the state, which had been collected as part of a separate study on chronic wasting disease.
Cougar eat almost nothing but white-tailed deer, which have small stationary ranges.
The variation they saw in the hydrogen-deuterium ratio on the map matched the pattern seen in precipitation, while the higher proportion of carbon-13 in the east of the state were attributed to the presence of cornfields there.
The scientists then compared the cougar's claw with the maps.
With either just the hydrogen or the carbon information, it would have been impossible to trace the animal's route. But by overlaying the maps, and thereby narrowing down the possible locations for each time step, Henaux was able to infer that the cougar followed the Missouri or Elkhorn River from the Black Hills of South Dakota.
According to Hobson, most tracking has been done on a global or continental scale, determining where migratory birds overwinter, for example.
"The work with the cougar revealed that this could be at the state scale; I think that was an exciting breakthrough," he said.
Henaux said that the technique could be used with other large mammals-both as part of anti-poaching efforts and to help land managers plan where wildlife corridors should be set up.