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Dissecting Dispersal

Written by Tabitha Graves, SoGES 2013-2014 Sustainability Leadership Fellow and David H. Smith Post-Doctoral Conservation Research Fellow in the  Department of Fish, Wildlife and Conservation Biology

Have you ever wondered whether animals face the same tough choices as a teenager leaving home for the first time? I do! I study grizzly bears and I am very interested in dispersal, the process of moving away from the place of birth to a new place. I wonder about how bears will wind their way through snow-capped mountains, cross roads, and wander along steams, and whether they will make their home surrounded by wilderness or next to a subdivision. Learning the answer to this will help us plan where we should put our homes and roads.

 

This two-year old bear, has to answer three key questions:

  1. Should I leave home?
  2. Where should I go?
  3. What route should I take?

It turns out to be pretty difficult to catch and track young bears. So, I thought, ‘Maybe, just maybe, we can learn about dispersal if we only know where bears are born and where they end up.’ My collaborator, Kate Kendall, collected hair from bears for 13 years in northwestern Montana. The hair has DNA, which I used to make a grizzly bear family tree. I know, cool, right? I love my job!

Here are a few boughs of the family tree I created (parents at the top, great- grandcubs at the bottom).  A few exciting details:  Bear 1 (female) has at least 3 daughters, 1 grandson, and 2 great-grandcubs.  Bear 4 (male) has at least 5 offspring, 1 grandcub, and 2 great-grandcubs. This gets even more fun when we look at where we caught the hair. For example, we caught the hair from bear 2 along with bear 35 and 38 at the same location. Do you think these two bears had not yet dispersed?

Now, by using the mom’s location as the origin and the young’s location as the end of the dispersal, along with a statistical model I developed, I can answer questions about the way people and habitat influence where these young bears will go! For instance: 1) Do bears move further when they come from places with a big family? 2) Are young bears likely to find a new home amidst lots of wet meadow vegetation? and 3)  Will grizzly bears cross a huge highway while they are leaving home?    

The answers I find can be used to manage land and people in ways that will keep bear populations big and connected. The methods I am developing are useful for understanding movement and dispersal for other species, like kinkajou, too. Now! I can’t wait to find out what bears do when they leave home.

*The grizzly bear data I am using was collected by U.S. Geological Survey researcher Kate Kendall between 1999 and 2012, in collaboration with 5 national forests managed by the U.S. Forest Service, the U.S. Fish and Wildlife Service, Montana Fish, Wildlife, and Parks, the Blackfeet Nation, and the Salish and Kootenai tribes, and many more.   I greatly appreciate everyone’s assistance with collection of this rich data.

The photo above shows a young grizzly bear in a spring rainstorm in Glacier National Park who is walking away from her mom who was clearly pre-occupied with mating. Perhaps this may be the very moment it began to disperse.

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