Stable Isotopes And Cougar Dispersal Patterns

Mammals

Cougar populations in Midwestern North America have been recolonizing some of their former ranges in recent decades, however the dispersal routes taken from established populations by these animals are unknown. Insight into these patterns and movements is of the utmost importance in facilitating cougar conservation and management. Most confirmed cougar sightings in the Midwest are young males suggesting that juveniles are likely displaced from established populations and set off to find their own territory to avoid inbreeding and competition for resources. The use of isoscapes as a tool in animal migration research has not just been valuable in a range of animals but also show potential in the area of archaeological human origin studies, as demonstrated by Laffoon (2017).

Alexis et al (2012) developed an isoscape method for determining the probable origins of bats within hibernacula. This approach can be used to estimate both annual and seasonal flight distances of cave dwelling species but also to provide insight into foraging and migratory patterns and strategies within bat populations, it could also become a tool in monitoring diseases such as white-nose syndrome which is currently devastating bat populations of North America and Canada. “Cave dwelling bats primarily escape seasonal fluxes in resource availability through hibernation, but the natural rarity of suitable hibernacula may prompt annual migrations between seasonal roosts.

Methods

Four dispersing cougars were studied by Hénaux et al (2011), two of which died in vehicle collisions, and two which had been shot. Stable hydrogen and carbon isotope values were studied along their claws. Working backwards from their final locations, the most likely dispersal route of each animal was predicted by comparing carbon and hydrogen values within the claws to regional and large-scale isoscapes in prey species. Cougar claws continuously grow resulting in a temporal dietary time series record. Deer tissues were used to access local variations.

Laffoon et al (2017), applied and compared two approaches for utilizing Sr and O analyses and associated isoscapes for human geoprovenance purposes in dental enamel of both modern and archaeological samples in the Circum-Caribbean. Isoscape approaches require tissues of known origin, which for bats requires sampling within the molt period, this can then be used to determine the geographic origins of a hibernating bat population. Alexis et al (2012) deployed this approach for little brown bat populations in three mines in Western Michigan.

Results

Two of the cougars had previously been captured and radio marked which allowed researchers to confirm results obtained from their isoscape studies and they confirmed that these were indeed accurate to locations already confirmed. Because this tissue is metabolically inert after synthesis claws or other material collected several years ago from accidents or hunted animals could still be useful for isotopic analysis and aid in identifying routes or areas of importance.

One problem with studying the claws was that the oldest information found at the tip is constantly been worn away which does not always make it possible to identify the animals original location, however when combined with another method results can be more conclusive. The study did allow the team to correctly identify the journeys of these animals however it does not give any information about changes in speed and direction.

Following their study Hénaux et al (2011) encouraged managers to “extend regional isoscapes based on sedentary prey species as they prove to be valuable tools in the tracking of long distance migration”. Similar studies in archaeological research have been lacking to date owing in part to the absence of relevant (bioavailable) large-scale strontium isoscapes for most regions of the world. , but have potential for future applications.

All of the geographic assignment methods described in these studies are only as reliable as the underlying isoscapes upon which they are based, therefore the overall success of these geoprovenance methods would be most readily and effectively advanced by improving the underlying isoscapes. The accuracy and precision of geographic assignments may be further improved by better understanding of the relationships between environmental and biological isotope variation, continued development and refinement of relevant isoscapes, and the eventual incorporation of a broader array of isotope proxy data”.

Being able to identify connectivity between animals is crucial for conservation and management decisions and plans demonstrated here in particular among regional bat hibernacula enabling resource managers to consider hibernacula closures, culling select populations and for understanding metapopulation dynamics among regions.