Predicting origin and migration route of cougars using stable isotope gradient in claws

Background/Question/Methods

Recolonization of midwestern North America by cougars (Puma concolor) provides an opportunity to study dispersal pathways from established western populations. Determining the migration routes of these top predators is of critical importance to implement efficient management plans. But, because of logistic problems linked to long-term monitoring of these secretive animals, dispersal corridors remain unknown. Recently, biologists have employed stable isotope analyses of specific animal tissues as a powerful approach to determine an animal's previous locations and hence, infer origin and long-distance dispersal. To determine the origin and migration route of a cougar road-killed in eastern Nebraska, we intersected hydrogen (dD) and carbon (d¹³C) isotopic values along one of its claw with base maps of D and ¹³C for Nebraska. The claw is a tissue metabolically inert after synthesis but that grows continuously, integrating site-specific dietary information over a suitable temporal scale to assess the migratory path of large carnivores. We obtained the isotopic base maps by measuring the concentration of these isotopes in lymph nodes of white-tailed deer (Odocoileus virginianus), the cougar's main prey species.

Results/Conclusions

Deer lymph nodes produced a west-east dD gradient that matches the known deuterium pattern in precipitation. The carbon isotopic gradient reveals higher d¹³C values in eastern Nebraska than in the Great Plains, a results of the higher importance of corn (C₄ plant) than herbaceous plants (C₃ plants) in white-tailed deer diet in eastern Nebraska. The variation in dD values within the claw suggests an initial period spent in South Dakota's Black Hills, followed by a recent long-distance migration. The multiple isotope analysis reveals that this cougar travelled east through southern South Dakota or northern Nebraska, before following the Missouri and/or Elkhorn rivers through northeastern Nebraska. Our study highlights the potential of analyzing claw isotopic gradients to track movements of large predators; stable isotope analyses do not have problems of detection probability or tag loss met with time-consuming capture-recapture or telemetry methods. We suggest that our technique could allow ecologists to study large-scale movements of other large carnivores.