Tuesday, January 15, 2013

Bighorn Sheep Follow Up

For those of you that might not have checked out the comments on my last post, I wanted highlight a comment from Jesse DeVoe on that post. Jesse is a graduate student at MSU as part of The Greater Yellowstone Area Mountain Ungulate Project. The ewe bighorn I had the photo of is one of the study animals in this project.

As Jesse explained, the two collars on the ewe serve different purposes and this is further explained in the following from the projects website
"The dual collaring strategy involves the deployment of both a GPS and VHF radio collar on a
single individual.  The advantage of GPS technology is that it provides fine-scale (precise)
spatial data at regular, relatively short, time intervals. Such data are optimal for addressing
questions of spatial ecology.  Spatial studies will provide insights into movement dynamics at the
scale of individuals important in defining discrete populations, identifying migration pathways
and corridors, and describing patterns of fidelity, dispersal, and metapopulation dynamics.  GPS technology is the most appropriate method for this effort as detailed spatial studies would requireintensive and extensive aerial surveys if VHF telemetry were used.  The unpredictability of flying weather and the inherent hazards of flying in mountainous terrain would limit both the
spatial and temporal resolution of the data and, thus, erode the potential ecological insights that
can be gained from such an effort.
The disadvantage, however, of GPS technology is that deployment on animals is limited to
approximately 1 to 2 years due to short battery life which limits their utility for collecting
demographic (survival, reproduction) data.  The VHF collars, on the other hand, have the
capacity for long term deployment (about 5-8 years) and are optimal for addressing questions of population dynamics. Understanding and estimating the basic vital rates of the populations, that is survival and reproduction of adults and survival and recruitment of young-of-the-year, is
important knowledge for managing and conserving populations. In ungulates, these
demographic processes are age-dependent and can vary from year-to-year depending on
variability in warm and cold season weather which, in turn, influences forage quantity, quality,
and availability. VHF telemetry is a simple, reliable, and economical tool for long term survival
and reproduction studies of individual animals. Thus, the combined instrumentation of GPS and
VHF collars on individuals will serve to integrate and maximize ecological insight in an efficient
 More information on the telemetry part of the study, including capture techniques, immobilization, and more specifics about the collars can be found here (PDF).

Judging from what I could find in this document, this individual is marked as either B or C based on the location of the white mark (duct tape) on the brown collar (you can see the stripe across the collar just behind this ewe's ear) and she is part of Upper Yellowstone study site (did I get this right Jesse and might you have any further info I could share on this particular ewe?).


MTWaggin said...

Hey that is pretty interesting. Amazing the things we can learn by just adding a collar to these animals. Wish I'd have seen them when I was down there (I tried to no avail) maybe I should have been asking the study group! :)

JK said...

Very interesting. Do the researchers use the VHF to find the individual and replace the GPS battery when it is going dead, or do they just let the GPS die and that individual drops out of that part of the study?

Jesse DeVoe said...

Hey John,

Where specifically did you see this collared ewe? She was definitely collared in mid-Feb last year, but our collar marking technique this time around wasn't the best (looks like the tape is coming off and may have come off another part of the collar...we're still perfecting that), so I'm not sure which one she is. (Though we don't have much information on her, since it only been less than a year of the study)

And to JK,
The GPS will collect spatial data for a couple years until its battery dies, then will fall off to be recovered, which is when the VHF is set to turn, so we can continue to find her for about 7 years before that battery dies. This will allow us to assess if she has reproduced, and see if her lamb survives the summers (and following winters). We will also use it to assess her survival.

John Carlson said...

Thanks for the info Jesse. This ewe was just off the north side of highway 89 about a mile northwest of Gardiner.