Over the next several weeks wildlife biologists from Fish and Game’s Magic Valley Region will be flying surveys for mule deer and elk across many of the region’s game management units. The purpose of these surveys is gather abundance and herd composition information that help game managers understand population numbers and trends.
Area residents may see the survey helicopter flying low over the landscape over the next several weeks.
Wildlife biologists survey big game populations using helicopters
Herd composition surveys for deer will happen in the Bennett and Picabo hills and Jasper Flats north of Picabo, as well as in the Sublett, Black Pine and Jim Sage mountains and the South Hills.
Abundance surveys for elk will be conducted in the Pioneer Mountains and for mule deer in the Sublett and Black Pine mountains of southern Idaho.
In late December and early January helicopter operations will also be used to place radio collars on mule deer and elk using a net gun to capture the animals. This information is used to estimate winter survival and document seasonal movements.
Logistics of surveys
Many assume that Fish and Game conducts deer and elk surveys in every unit, every year. While this may seem logical, there are many different factors that influence how often population counts can occur across the state.
A population survey takes a significant amount of personnel time and resources to complete. Combine these costs with very high hourly costs to fly helicopters, upwards of $1,000/hour, and the combined costs can easily exceed the annual budget allocated for population monitoring.
Add ever-changing weather and snow conditions to the mix, and what is thought of as a straight-forward task can become extremely difficult to complete.
Herd composition survey
Mule deer herd composition surveys are performed annually in many Data Analysis Units (DAUs) across the state. A DAU, or Zone for elk, is comprised of multiple game management units. These surveys are typically flown in early December to estimate fawn:doe and buck:doe ratios. Early winter fawn:doe ratios is a measure of fawn productivity for the first six months of life, and is an important component to model and estimate deer populations into the future. Likewise, calf:cow and bull:cow ratios are gathered for elk.
View across the landscape from a helicopter during a big game winter survey
Herd composition surveys cover areas representative of deer distribution in a given area and classify enough animals to accurately estimate composition. A composition survey of 750 or 1,000 deer is fairly typical in most DAUs and is considered a large enough sample size to accurately estimate the composition of the entire population.
A herd composition survey may take up to two days.
While the primary purpose of a composition survey is to acquire reliable fawn:doe ratios, buck:doe ratios are also obtained at the same time. However, because bucks are in smaller groups and occupy different areas on the landscape than does and fawns, buck:doe ratios are inherently conservative and typically underestimate buck numbers.
Abundance surveys
An abundance survey counts deer or elk within a specific DAU or elk Zone by flying a grid across winter ranges within the DAU or elk Zone. Typically, these surveys are flown with a helicopter every 4-5 years.
A typical abundance survey may take several weeks to complete, and are typically flown between mid-January and early March to ensure deer and elk are concentrated on low elevation winter ranges.
Not all deer or elk are observed during an aerial abundance survey. There are a number of reasons why. Thick vegetation can conceal animals from observation and the lack of snow cover can make deer and elk more difficult to detect. In addition, animals on the move or in large groups are much easier to observe than small groups of bedded animals. Because of this, Fish and Game has developed a “sightability model” which corrects the count to include animals not observed during 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.
Many western states have now adopted Idaho’s survey protocols and sightability models to estimate their own big game populations.
For more information about big game management contact any Fish and Game Regional Office.