gwave47 wrote:Peakhugger, I would even challenge that map. I just can't believe that there would be a population in Yellowstone and South West Montana, then another population beginning north of Helena, but nothing in between. I just find it hard to believe that there aren't grizzlies between Helena and Bozeman, when they are just north and south of these areas. Wouldn't the two populations slowly migrate towards each other until they fill in the gap.
This is a fair question. I can tell you at this point, FWP has no confirmed resident
grizzlies north and west of the Tobacco Roots and south of MacDonald Pass. There are rare reports of sightings of transient
griz in the gap, including at least 2 positively confirmed grizzlies in the Butte area in the last 5 years, one north and the other west. (There's another possible corridor in the Big Belts/Bridgers that I don't have any info on.) There are a few possible explanations for this absence:
1. Grizzlies are slowly colonizing these areas, but have yet to close the gap
2. The habitat isn't as ideal, either in quality or volume (resource limiting)
3. Human presence is greater with fewer quiet places for grizzlies to exist (griz behaviorally avoid this area)
I would personally favor #1. This stems from reports over the years of more griz sighted south of the NCDE and north of the GYE. Griz may just be recolonizing these areas slowly, possibly as a function of increased dispersal due to increasing pop densities in the NCDE and GYE. But there are likely truths in #2 and #3 as well. The habitat, particularly in terms of human influence and road density, may not be able to support "high" population densities of grizzlies. It's also a lot drier, which from my limited observations doesn't support as many berries or other preferred griz foods (the Boulder Batholith between Helena and Butte is particularly dry and sandy). See the references below for more info.
FYI: here's one example of estimated habitat suitability for griz in the northern Rockies (developed from Craighead Institute data):
Note the lack of good, continuous habitat between the NCDE and GYE. However, also note the expanse of suitable, but nearly unoccupied habitat in the Bitterroot/Idaho. Hopefully grizzlies will recolonize that area with resident bears soon. The first confirmed bear
in that area was shot in 2007.
A small sample of literature for the ecology nerds like myself:
Kendall, K. C., Stetz, J. B., Boulanger, J., Macleod, A. C., Paetkau, D. and White, G. C. (2009) Demography and Genetic Structure of a Recovering Grizzly Bear Population. The Journal of Wildlife Management, 73:3–16.
Mace, R. D., Waller, J. S., Manley, T. L., Ake, K. and Wittinger, W. T. (1999) Landscape Evaluation of Grizzly Bear Habitat in Western Montana. Conservation Biology, 13:367–377.
Mattson, D. J. and T. Merrill. (2004) A model-based appraisal of habitat conditions for grizzly bears in the Cabinet-Yaak region of Montana and Idaho. Ursus 15 Workshop Supplement:76-89.
Nielsen, S.E., G. McDermid, G. B. Stenhouse, and M. S. Boyce. (2010) Dynamic wildlife habitat models: Seasonal foods and mortality risk predict occupancy-abundance and habitat selection in grizzly bears. Biological Conservation 143:1623-1634
Schwartz, C.C., M.A. Haroldson, and K. West, editors. (2010) Yellowstone grizzly bear investigations: annual report of the Interagency Grizzly Bear Study Team, 2010. U.S. Geological Survey, Bozeman, MT.