(Idaho State) Beginning at the end of January and for the few weeks, wildlife biologists from several regions in southern Idaho will be flying a mule deer abundance survey on winter range in the Smoky-Boise DAU, which includes portions of Units 39, 45, 48, 49, 50, 52, 52A, and 53.
Two to three helicopters will be used because of the large area encompassed by this survey, which contains Idaho’s largest mule deer population and includes extensive big game winter range.
To put it simply, a Data Analysis Unit (DAU) represents the entire seasonal range for an interbreeding population of mule deer, including summer and winter range, and migratory routes. Idaho’s DAUs were developed with location data from mule deer fitted with GPS radio collars across the state.
What is an abundance survey?
An abundance survey counts deer within a specific DAU by flying a predetermined flight pattern across winter ranges within the mule deer DAU. Typically, these surveys are flown in a helicopter and are flown in a similar manner every 5-6 years so there’s a reliable comparison between the current and previous surveys
A typical abundance survey may take several weeks to complete and is usually flown between mid-January and early March to ensure deer are concentrated on low elevation winter ranges.
Not all deer are counted, for a variety of reasons. Thick vegetation can conceal animals from observation and the lack of snow cover can make deer more difficult to detect. In addition, animals on the move or in large groups are much easier to see than small groups of bedded animals. Because of this, Fish and Game has developed a “sightability model” which accounts for animals that are missed or hidden during the survey.
As an example, a survey might physically count 10,000 deer on a winter range, but the sightability model will correct the estimate for those deer not seen. The model could “correct” the population estimate by 10-20%, depending on the conditions (snow cover and vegetation) and animal behavior (group sizes and activity) at the time of the survey.
Give us a break with the acronyms – what’s a DAU?
While hunters tend to be more focused on specific hunting units – or even specific drainages – in the fall, biologists are looking at a larger population as a whole, and because of the migratory nature of mule deer, that extends beyond hunting unit boundaries.
Fish and Game collects its population data in the winter, when mule deer are congregated on winter range. Among the deer that disperse from winter range in the spring, different herds go to different summer ranges. Conversely, herds that occupy the same summer range may winter in separate areas.
By using these large DAUs as the sampling unit for mule deer management, biologists ensure that the data collected in the winter and the hunter harvest reports from the fall apply to the same herds. That is critical to developing appropriate management recommendations.
Why abundance surveys are important for mule deer management
As we mentioned earlier, abundance surveys aren’t an annual occurrence – they’re labor intensive, expensive, and the areas they cover are simply too expansive to fly every year, and there’s not enough aircraft and personnel to do it annually. Fortunately, they don’t need to be.
Based on decades of data gathered from herd composition surveys, abundance monitoring, survival monitoring and hunter harvest information, Fish and Game can model annual deer abundance between survey years in some mule deer populations. When the comprehensive abundance surveys do come around, however, they are critically important for refining and verifying Fish and Game’s population modeling.
Although helicopters can disturb wintering herds, it’s very short in duration, only occurs once, and does not affect their health or winter survival.