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 aMore information on the telemetry part of the study, including capture techniques, immobilization, and more specifics about the collars can be found here (PDF).
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
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?).