Research shown effective for management, less so for science
Helicopter deer surveys are a popular way for hunters and landowners to keep track of their deer and are a cost-effective way to do so on large properties. An issue with the surveys is that they are a single point estimate, and statistically the results don’t meet the rigors of science without some treatment. Hunters, though, care most about whether they can rely on the results on their ranch.
At the recent Caesar Kleberg Wildlife Research Institute Deer Research Meeting, Dr. Aaron Foley presented the results of a scientific investigation on the accuracy of helicopter surveys to capture ratio data for deer herds. The examination found estimates of buck:doe and doe:fawn ratios were accurate for deer management, but not as reliable for buck:mature buck ratios.
A helicopter survey is flown at a relatively low level to flush deer, and the crew count and classify deer as they are observed. The data gathered are used to estimate ratios within herds, commonly buck:doe ratios and doe:fawn ratios. In some more intensive management programs, surveyers also try to classify bucks further into young bucks and older, mature bucks in order to estimate the recruitment into the trophy class. Survey flights are conducted along flight transects with the goal of observing between 25 and 50 percent of the habitat in the area.
Using survey data from the King Ranch in South Texas, Foley and his researchers examined survey data for statistical variance in the three ratio groups to determine how much effort is necessary to provide research level data and management level data. To be considered scientific enough for research publication, the data from the counts must fall within no more than 25-percent variance, while for data on ratios to be useful for management purposes, they must have no more than 50-percent variance.
Looking at doe:fawn ratios, the scientists found only 31 percent of the surveys were accurate enough to meet the research threshold, but 90 percent of the surveys were accurate enough for management purposes. Buck:doe ratio analysis showed 36 percent of the surveys adequate for research, but an astounding 99 percent were accurate for management use.
Using these numbers, they also looked at the number of unique observations necessary to monitor the ratio within the herd. A unique observation is an individual sighting at a single point, whether that is a single deer or a herd or family group. They found that a survey must have between 45 and 60 unique observations to meet the standard for management, but between 210 and 230 unique observations to be research-grade data.
For this reason, most of the young buck:mature buck data failed to be useful at any level. Finding 45-60 bucks in a survey is difficult, finding 210-230 is almost impossible.
Foley pointed out that environmental conditions can also alter the accuracy of survey data. During drought years, surveys may need to be more intensive because the individual sightings may be lower. Landowners may be tempted to increase the number of survey lines to obtain a higher number of observations, but run the risk of double-counting, which makes the data unusable.
Surveys are frequently flown in September to meet the management planning of landowners and hunters.
