Experimental Season Results

For eight hunting seasons (2013 to 2020) the Texas Parks and Wildlife Department (TPWD) tested an experimental buck pronghorn season in the Dalhart and Pampa areas. The experiment allowed landowners to control the harvest of buck pronghorn on their properties. This was different than the current statewide regulations where TPWD determines harvest quotas and issues permits directly to landowners using data from annual population surveys. During the eight hunting seasons, TPWD biologists collected data via mandatory check stations that required hunters to bring their harvested bucks to a check station within 24 hours of harvest as well as annual aerial surveys. These data were used to help evaluate impacts of the experiment on our pronghorn resource. Although the experimental area pronghorn population numbers and fawn reproduction mirrored those populations outside of the experimental areas (indicating no negative population level impacts), we documented some other effects.

Summary

Conducting this experiment has provided TPWD biologists with tremendous datasets of new information regarding the upward limits of pronghorn buck harvest. We would have never known these bounds without trying the experiment. In terms of pronghorn population sustainability, the experimental harvest strategy seemed to have no impact on local populations. However, the level of buck harvest intensity within the experimental areas had unnatural effects on sex ratios and buck age structure. Data suggest without using annual survey data to establish harvest recommendations and issuing permits for each property in landscapes and hunting pressure such as in the experimental areas, pronghorn buck age structure and sex ratios will continue to be adversely impacted.

Results for Buck Pronghorn in the Northern Panhandle

Harvest Intensity

On average, permit usage for buck pronghorn in the Panhandle is about 55%. This means that of 100 buck permits issued by TPWD to landowners each year, approximately 55 get used. These permits are allocated to landowners using data collected from aerial surveys each summer. The graph below signifies permit utilization (or harvest) in relation to the recommended buck harvest from TPWD based upon annual aerial survey data collected in the experimental areas. In the year prior to the initiation of the experimental concept (2012), permit utilization was 85% in the Dalhart area and much lower for the Pampa area with only 45% of the permits being used. In contrast, the average harvest rate during the experiment was significantly higher in each area.

experimental Areas actual harvest relative to recommended harvested chart

Sex Ratios

TPWD biologists use population sex ratios as another guide to harvest intensity. During the experiment, only bucks were harvested, so higher buck harvest rates have the potential to reduce buck numbers within those areas. This higher buck harvest can cause sex ratios to become abnormally skewed toward does. Sex ratios are illustrated in the chart below, which are estimated when TPWD biologists conduct aerial surveys in June/July each year. The 2011 and 2013 average sex ratio was estimated during the summers prior to initiating the experiment in the fall of 2013 (blue bars). The orange bars represent the average sex ratio from 2014 to 2020, seven years after the start of the experiment. In both experimental areas the sex ratio has increased with a more drastic rise in the Pampa area. The Panhandle category embodies all other herd units in the northern Panhandle not included in the experiment. These areas have a more limited harvest because TPWD determines harvest quotas and issues buck permits for surplus pronghorn. Because of this system sex ratios were more stable and natural in the areas outside of the experiment during the same timeframe.

sex ratios estimated by aerial surveys chart

Age Structure

Analyzing the age of harvested bucks provides additional information regarding buck harvest intensity. These data were derived from pulled incisors from harvested bucks that were brought to our check stations. A process called cementum annuli forensic aging was used to estimate ages of harvested bucks, similar to counting rings on a tree. The 2012 age data, the year prior to the experiment, were used as the benchmark for comparisons in each area to the average age during 2013 to 2020. In the Pampa and Dalhart areas, the average age of harvested bucks decreased by 0.7 and 1.0 year, respectively. This is a significant shift in the buck age structure and highlights a high buck harvest.

age structure of harvested bucks chart

Horn Growth

Other data collected by TPWD biologists at check stations included horn measurements from each buck brought to check stations. Biologists measured one horn, which comprised of 4 circumferences, horn length, and prong length. These measurements were collected to the nearest 1/8 inch. Again, ages were derived from incisors pulled from each buck measured. These data were then put into age categories such as 1.3 to 7.3 years old. The graph below portrays basic horn measurements by each age group. Peak horn development occurred within the 5.3 age class. However, unlike deer, on average pronghorn bucks achieve over 95% of their maximum horn development at 3.3 years of age. This provides some buffer in maintaining horn quality with higher harvest rates of bucks. Striving to harvest bucks 3.3 years of age or older will provide maximum opportunity, while keeping horn quality high.

horn measurements taken from harvested bucks chart