Ground-based cameras show promise for measuring mule deer fawn ratios in certain areas of Idaho

For the past three years, Fish and Game staff in Southwest Idaho have been evaluating the effectiveness of remote cameras in Unit 32 to estimate mule deer herd composition, which is a key measure that helps wildlife managers understand recruitment and overall mule deer herd condition over time. The results so far have been promising: In each year of the project, these ground-based cameras in the Weiser-McCall mule deer population produced fawn ratios nearly identical to those from traditional aerial surveys, suggesting remote cameras could offer IDFG a reliable, lower-risk tool for monitoring certain deer populations.

IDFG conducts aerial surveys each December across southern Idaho to assess post-hunting season mule deer herd composition. These are relatively short surveys where we aim to count a sample of at least 1000 deer in each data analysis unit (DAU).  A DAU is comprised of multiple hunting units and represents the seasonal range for an interbreeding mule deer population.

One of the metrics we look at is the fawn:doe ratio, which is recorded as the number of fawns per 100 does. In the Weiser-McCall DAU, we observed a fawn ratio of 60 fawns:100 does last December (2025) which is near the long term average of 59 fawns:100 does since 2011. 

Aerial surveys are expensive, time consuming, weather dependent, involve risk to staff, and helicopter availability is low during that time of year. Because of this, IDFG is constantly evaluating other, potentially safer or more efficient ways to obtain deer composition data. 

Over the last decade, wildlife agencies have increasingly used remote cameras to monitor wildlife populations. Biologists in the Southeast and Southwest regions have used cameras to assess fawn and calf ratios respectively along migration routes to winter range.  We’ve been able to use radio-collar data to identify several mule deer migration routes along north-south ridgelines on the east side of Unit 32. During the last three years, staff have been evaluating sites to place cameras along these routes to sample part of the Weiser-McCall deer population.  

We located a narrow area on one of the north-south ridgelines where deer moved through quickly and didn’t appear to stop and mill around. This was important to reduce the chance that we would get multiple photographs of the same deer. In 2023, we placed 10 cameras on 10 game trails in this narrow area. Cameras were deployed in October and retrieved by late December to ensure we caught the majority of the migration. SD cards were processed back at the office where staff examined every photo to count and classify deer that passed by the camera. We used those counts to get our fawn:doe ratio.  

The first year was a learning experience. There were multiple cameras knocked down or sideways by rutting bulls and bucks. People pulled two cameras from their posts, opened them, and stole their SD cards.  Several game trails received very little deer traffic, and therefore few deer photos. In spite of all this, we managed to get 609 photos of deer and calculated a fawn:doe ratio of 61:100 which was very similar to the aerial estimate that year of 62:100.

We learned from the first year and, in 2024, set cameras only at the three best spots identified in 2023. We built gabions around the camera posts and placed cameras in security boxes to fix the issues we had with tampering and to protect cameras from animal rubbing. Again, the fawn:doe ratio from cameras (73:100, table 1) was remarkably similar to that obtained from the helicopter in 2024. 

The effort was repeated in 2025 using the same camera setup and locations. Once more, the fawn:doe ratio for the cameras was nearly identical to what was observed on the aerial survey, 59:100 vs 60:100. 

This method shows real promise for collecting fawn:doe ratios in certain areas. That said, it won’t ever fully replace the need to fly surveys. For instance, this level of detail in radio-collar data isn’t available for all deer populations in the state which makes identifying specific, narrow migration routes problematic. Additionally, not all wintering populations have migration routes that lend themselves to being photographed by only a few cameras. Nevertheless, it shows promise as a viable method in specific populations. IDFG will continue to investigate and improve methods to manage wildlife.