Interesting study on culling.
Livestock Weekly
March 24, 2011
South Texas Buck Study Reveals Interesting Results On Culling
By Colleen Schreiber
SAN ANTONIO — For deer enthusiasts, particularly those doing the managing of the deer herd, deciding what to cull, when to cull, how to cull, or whether to cull at all is no simple task. Evaluating whether a culling program is helping accomplish the established goals is a whole different issue. Better yet, does culling really affect the genetics of that herd?
Those were some of the tough but pertinent questions that Dr. Mickey Hellickson, wildlife biologist and principal of Orion Wildlife Management Services, attempted to address during an educational seminar of the Texas Deer Association. The title of his presentation, "The true value of culling and its lack of effect on genetics" — gave away his thoughts on the subject. To get to the heart of the matter, Hellickson first identified three specific questions that had to be answered to sufficiently address the overall question about culling — does it work?
The questions he identified were: When does antler size peak? Are spikes inferior? What culling criteria should be used?
To address these specific questions, Hellickson used data from the South Texas buck capture project, initiated in 1998 by the Caesar Kleberg Wildlife Research Institute at Texas A&M-Kingsville, where Hellickson at the time was a research scientist. The study was conducted on five South Texas ranches.
Specific to the first question — when does antler size peak — researchers collected 4827 capture records from 3098 individual bucks over a 13-year period. About five percent of the unique bucks captured had a gross Boone and Crockett score above 150, two percent were above 160, and only half a percent scored above 170. Four out of 3098 bucks grossed above 180, two out of 3098 grossed above 190, and only one buck in 13 years involving nearly 5000 capture records gross scored above 200.
"That gives you an idea of how rare those really big native deer are in the wild," Hellickson told listeners. "In fact, the average gross score of the bucks captured in this study that were 5.5 years or older was 130."
Using buck capture records from known aged deer, (these are deer that were initially captured as either buck fawns or as yearling bucks that were released and then recaptured at 2.5, 3.5, 4.5 on out to 8.5 years of age), researchers determined that antler size peaks around 6.5 years of age. They also measured chest girth of these same bucks, and the data indicated that chest girth doesn’t peak until about 6.5 years of age and in many cases not until 7.5 years of age.
Hellickson reminded listeners that age is not the only factor that affects antler size. Spring rainfall, for example, is critical. This was demonstrated by more data gathered from the Faith Ranch in Dimmitt and Maverick counties. From 1985 to 1994, Stuart Stedman, Faith Ranch owner, kept track of the average gross B&C score for mature bucks, those 5.5 years of age or older, live captured on his ranch. During the dry spring of 1988 the average gross B&C score was 121 inches. However, during the wet spring of 1992, the average B&C score was 141 inches.
"Spring rain alone accounted for as much as a 20-inch shift in gross B&C score for mature bucks," said Hellickson, "and spring rain explained 70 percent of the year to year variability in antler size."
On the South Texas buck project, researchers also found a high correlation between spring rainfall, March through May, and the number of 160 inch or bigger bucks harvested the following fall on the King Ranch. Given that, for those interested in trophy buck management, Hellickson recommended harvesting bucks at 5.5 years of age during a wet spring for the simple reason that the chances of getting two good years in a row are slim and therefore antlers are not likely to be better the next year. When spring rainfall is normal or below normal, Hellickson recommended delaying harvest until bucks are at least 7.5 years of age.
The next question, are spikes inferior, is a question that is old as — well, it’s old. It’s certainly been debated for decades, and it’s still being debated.
To answer this question, Hellickson again turned to data collected from the South Texas buck capture study. Researchers calculated the average gross B&C score of yearling bucks with two to three antler points versus the average gross B&C score for yearling bucks with four or more antler points when those bucks were recaptured at 2.5, 3.5, 4.5 on out to 7.5 years of age.
In every age class, the bucks that were forked antlered as yearlings outscored the bucks that were spikes as yearlings. In the 4.5 age category the gross B&C score of the bucks that were spikes as yearlings ranged from 85 inches to 145 inches, with the average being 116 inches. However, the gross B&C score of the bucks that were forked as yearlings when recaptured at age 4.5 ranged from 90 to 160 with an average of 130. Looking at the data another way, 11 of the 15 bucks that had a gross B&C score under 110 were spikes as yearlings, Hellickson said, and 12 of the 13 bucks scoring above 140 were forked antlered yearlings.
In the 5.5 age category, the bucks that were spikes as yearlings had an average gross B&C score of 125 while the forked antlered yearlings at 5.5 years of age had an average B&C score of 144, though one buck scored 210 inches. Looking at the same data another way, 13 of the 16 lowest scoring 5.5 year-old bucks were spikes as yearlings while nine of the 10 highest scoring bucks at 5.5 years of age were forked antlered yearlings.
They also compared spike yearling antlers to yearling bucks with six or more antler points at the various age classifications. In the 5.5 years or older category, researchers never captured a buck that was a spike as a yearling that grossed above 160. In fact, Hellickson noted that two-thirds of the bucks that were spikes as yearlings never broke 130 at maturity. However, only 18 percent of the yearling bucks with six or more antlered points failed to break 130 at maturity and 36 percent of the yearling bucks with six or more points broke 160 at maturity.
"So are spikes inferior? Based on our data set, we say yes. These data show that yearling antler size is a good predictor of antler size at maturity."
He added that all bucks that were spikes as yearlings were grouped together. In other words, they did not try to determine if the bucks were spikes as yearlings for nutritional reasons or for genetic reasons.
"In my opinion, it doesn’t matter whether a buck is a spike for nutritional reasons or for genetic reasons," Hellickson stated. "I say that because in this study, in every case, spikes were inferior to the forked group.
"A few spikes raised in pens have turned into big deer at maturity, but it’s rare," he continued. "But, in the wild, in this study we never had a buck that was a spike as a yearling gross score above 155," he reiterated. "I think biologists should never let the exception be misconstrued to be the rule when it comes to spike buck harvest."
As for the third question, the South Texas buck capture project also provided researchers with some good data that enabled them to develop definitive culling criteria for landowners to use. To do this they compared the number of points and the gross B&C scores of the bucks that were recaptured at various stages of their life.
Researchers captured 16, 3.5 year-old bucks with seven or fewer antler points that were recaptured at age 5.5 or older. One of those 16, Hellickson said, had a gross B&C score above 140 at maturity, but none of the 3.5 year-old bucks with seven or fewer antler points that were recaptured as mature bucks broke 150.
They also captured 41, 3.5 year-old bucks that had eight antler points. Two of the 41 had a gross B&C score above 150 at maturity and one grossed above 160 at maturity.
There were 13, 3.5 year-old bucks with nine points. Two out of the 13 grossed above 150 at maturity and one grossed above 160.
Additionally, researchers captured 40, 3.5 year-old bucks with 10 or more antler points. When these bucks were recaptured at 5.5 years of age or older, seven out of 40 broke 160 and 15 out of 40 broke 150.
"The odds were a lot higher that a 3.5 year-old buck with 10 or more points would break 150 or 160 compared to a 3.5 year-old buck with seven or fewer points," Hellickson explained.
For bucks in the 4.5 age category, researchers followed the same protocol. Over the course of the study, 85 bucks captured at 4.5 year of age had eight points or fewer. When those bucks were recaptured at 5.5 years of age or older, none of them grossed over 150.
"That tells me that it’s pretty safe to cull bucks that have eight or fewer points at 4.5 years of age," Hellickson told listeners, "because those bucks are not likely to gross over 150 at maturity."
They also captured 35, 4.5 year-old bucks with nine points that they were able to recapture at 5.5 years of age or older. Two of the 35 ended up above 150; one out of 35 (three percent) ended up above 160, Hellickson said.
Additionally, 75 bucks captured at 4.5 years of age had 10 or more points. Of those 75 bucks recaptured at maturity, 20 grossed over 150 while eight of the 75 grossed above 160.
Hellickson became the wildlife biologist for the King Ranch in 1998, a position he held for 12 years. He used data from the South Texas buck capture project to develop a culling strategy for the King Ranch. The culling categories which were designed and implemented beginning in the fall of 2001 were as follows: any buck with at least one unbranched antler, any buck 3.5 years of age or older with seven or fewer total antler points, any buck 4.5 years of age or older with eight or fewer total antler points, and any buck 5.5 years of age or older with gross B&C score less than 130. Any buck that did not fall into one of those four categories qualified as a trophy.
After implementing the non-quota cull buck categories, the buck harvest on the King Ranch increased dramatically while the harvest of trophy bucks declined. In fact, before the culling criteria were implemented, only about 24 percent of the bucks harvested on the King Ranch qualified as culls. After the culling program was implemented, 87 percent qualified as culls.
He showed a graph of the percentage of trophy bucks, those that grossed over 160, harvested on the King Ranch from 1998 to 2008. In 1998, five percent of the trophy bucks grossed above 160. In 2008 that number had increased to 22 percent.
"You might think, ‘Wow, the culling program really worked; bucks got bigger over time,’ but I don’t think that’s the case here," Hellickson opined. "Instead, what happened is we reduced the trophy buck quota so the hunters became more selective in what they shot as trophy bucks. And because of the increased selection, a higher percentage of the trophy bucks killed gross scored above 160."
What the culling program really did, he told listeners, is provide for a lot more hunter recreation.
"We forced hunters to shoot fewer trophy bucks, but we gave them a lot more flexibility in harvesting cull and management type bucks."
Hellickson also told listeners that the culling criteria he implemented on the King Ranch could be considered "pretty conservative" for a South Texas ranch. On ranches that employ a more intensive management program, he suggested shifting the bar up a notch and culling yearling bucks with five or fewer points, 3.5 year-old bucks with eight or fewer points, 4.5 year-old bucks with nine or fewer points and, depending on harvest goals, perhaps consider culling 5.5 year-old bucks that gross score under 150.
So does culling work? To address this question, Hellickson turned to data gathered from the King Ranch culling study, which was being conducted simultaneously with the South Texas buck capture study. The culling criteria were established by TPWD based on results of penned studies from the Kerr Wildlife Management Area. The study was conducted on a 10,000-acre portion of the King Ranch. An adjacent 10,000 acres was designated as the control.
On the control area only five culls were removed over the course of the seven-year study. On the treatment area from 1999 to 2005 researchers removed 158 culls through gun harvest using culling criteria established by Texas Parks and Wildlife. That criteria included every yearling buck with fewer than six antler points and every 2.5 year-old or older buck with eight or fewer antler points, Hellickson said.
He showed a picture of a 2.5 year-old buck with a double drop tine that gross scored 128 captured on the treatment area during the first year of the study. That buck remained on the treatment area for the next five years while 125 inferior bucks were harvested from his neighborhood.
During the second year of the study the buck with the two drop tines was recaptured. At that time he had 17 points and gross scored 161. The following year he grossed 178; at age 5.5 he grossed 199. The buck was harvested the following year at 6.5 years of age. He grossed 190. The point Hellickson was making was that this particular buck offered researchers the perfect scenario to test their hypotheses.
Researchers kept track of the percentage of bucks captured by helicopter net gun on the two areas that still qualified as culls after the culling program was initiated.
"On the treatment area where we were selectively harvesting and removing all cull bucks you would expect the percentage of cull bucks captured at random to decline over time," Hellickson said. "However, after seven years of intensive culling, the percentage of bucks qualifying as culls on the two areas didn’t change. In fact, in the final year of harvest, 61 percent of the bucks captured at random on the treatment area qualified as culls and 61 percent captured at random on the control qualified as culls. We didn’t see any shift in the percentage of cull bucks between the two areas," Hellickson told listeners.
Additionally, at the end of the culling period they found no difference in the average gross B&C score of bucks on the treatment area versus the control.
Why, then, didn’t the culling program work on the 10,000-acre treatment area? One potential reason, Hellickson said, is that the culling criteria were less than ideal. Another potential problem, he said, was that the culling program was not flexible from year to year. For example, culling criteria did not change during a dry year versus a wet year. Additionally, both the treatment area and the control were low-fenced. Thus, researchers had a problem with bucks dispersing either from the treatment area to the control or vice versa.
They also found that some of the individual bucks that were recaptured multiple times changed their status as to whether or not they were considered culls. For example, during a wet year a buck had nine points, but if that same buck was recaptured later during a dry year, he might be considered a cull.
Still another possible explanation is that culling mistakes are made when gun harvest is employed.
"One of the worst mistakes one can make is to shoot a yearling buck that was mistaken for a seven point 2.5 year-old buck," Hellickson told listeners. "That’s why I don’t like culling the 2.5 year-old age class. Oftentimes the biggest yearlings look like small two year-olds and you don’t want to be shooting your biggest yearling bucks. Those are your future 160 or better bucks."
The final possible contributing factor as to why the culling study didn’t work has to do with individual buck breeding success. In an intensive DNA study, Dr. Randy DeYoung found that no matter the age or the size of the bucks, on average, bucks are only going to sire 1.5 fawns per year.
"So the very low buck breeding success likely contributed to the lack of results from the culling program."
To put the results in perspective he used what has become known as the "corral continuum" coined by Faith ranch owner Stuart Stedman. The idea is that the closer one moves toward a deer pen situation the more likely a culling program has a chance of success. The closer one moves to a free ranging, large acreage setting the less likely culling will be effective.
"On the King Ranch study we removed 43 percent of the culls that were available for harvest. We were only able to get eight percent of the culls removed before the breeding season. However, at the Kerr Wildlife Management Area deer pens, researchers removed 70 to 85 percent of the cull bucks annually and all were removed prior to the rut. In the latter case the pen data showed a huge improvement in antler size through selective breeding," commented Hellickson.
"That’s a very difficult thing to do on a ranch that’s very large," he continued, "because you’re talking about killing a whole lot of animals and doing it without making any mistakes and doing it all before the breeding season.
"The bottom line, then, is if you expect to see genetic change through culling, if you expect to see the kind of results that TPWD saw with their pen data, you have to have a small property and it must be high fenced. Those two things are mandatory," Hellickson opined.
Wrapping up, Hellickson reiterated that culling, in this particular study, did not increase antler size. Culling does, however, increase the opportunity for recreation, and increased recreational opportunity may translate into increased revenue. Additionally, in areas where deer density is at or near the maximum that the habitat will support, removing cull deer should have a positive nutritional effect on the remaining deer and that positive effect may translate into larger antlered bucks.
Finally, Hellickson said a culling program greatly reduces any chance of high grading.
"I think culling helps a lot to offset what we’ve done for decades, which was only harvest the biggest bucks we could find each year," he concluded.
In the Q&A Hellickson was asked to offer thoughts on doe harvest, and whether it was better to cull young does or mature does.
"My quick and short answer is if it’s an adult doe, shoot it," Hellickson responded. "I’ve heard a couple of opposing theories about the class of doe to target for harvest. My theory is if you have a high deer density and you need to remove deer, don’t worry about the age of the doe," he continued. "It’s difficult to age a doe on the hoof. You can tell the younger aged does, but telling a 2.5 year-old doe from a four or five year-old doe is difficult."
He was asked to expound on culling spikes in a dry versus a wet year. Though the South Texas buck capture project did not address this particular issue, Hellickson told listeners that it makes sense during a drouth year to slack off spike buck harvest because a large percentage, perhaps as many as 60 to 70 percent of the yearling bucks during a severe drouth, could be spikes. However, he added, such a decision is really ranch or manager-specific depending on one’s goals.
Livestock Weekly
March 24, 2011
South Texas Buck Study Reveals Interesting Results On Culling
By Colleen Schreiber
SAN ANTONIO — For deer enthusiasts, particularly those doing the managing of the deer herd, deciding what to cull, when to cull, how to cull, or whether to cull at all is no simple task. Evaluating whether a culling program is helping accomplish the established goals is a whole different issue. Better yet, does culling really affect the genetics of that herd?
Those were some of the tough but pertinent questions that Dr. Mickey Hellickson, wildlife biologist and principal of Orion Wildlife Management Services, attempted to address during an educational seminar of the Texas Deer Association. The title of his presentation, "The true value of culling and its lack of effect on genetics" — gave away his thoughts on the subject. To get to the heart of the matter, Hellickson first identified three specific questions that had to be answered to sufficiently address the overall question about culling — does it work?
The questions he identified were: When does antler size peak? Are spikes inferior? What culling criteria should be used?
To address these specific questions, Hellickson used data from the South Texas buck capture project, initiated in 1998 by the Caesar Kleberg Wildlife Research Institute at Texas A&M-Kingsville, where Hellickson at the time was a research scientist. The study was conducted on five South Texas ranches.
Specific to the first question — when does antler size peak — researchers collected 4827 capture records from 3098 individual bucks over a 13-year period. About five percent of the unique bucks captured had a gross Boone and Crockett score above 150, two percent were above 160, and only half a percent scored above 170. Four out of 3098 bucks grossed above 180, two out of 3098 grossed above 190, and only one buck in 13 years involving nearly 5000 capture records gross scored above 200.
"That gives you an idea of how rare those really big native deer are in the wild," Hellickson told listeners. "In fact, the average gross score of the bucks captured in this study that were 5.5 years or older was 130."
Using buck capture records from known aged deer, (these are deer that were initially captured as either buck fawns or as yearling bucks that were released and then recaptured at 2.5, 3.5, 4.5 on out to 8.5 years of age), researchers determined that antler size peaks around 6.5 years of age. They also measured chest girth of these same bucks, and the data indicated that chest girth doesn’t peak until about 6.5 years of age and in many cases not until 7.5 years of age.
Hellickson reminded listeners that age is not the only factor that affects antler size. Spring rainfall, for example, is critical. This was demonstrated by more data gathered from the Faith Ranch in Dimmitt and Maverick counties. From 1985 to 1994, Stuart Stedman, Faith Ranch owner, kept track of the average gross B&C score for mature bucks, those 5.5 years of age or older, live captured on his ranch. During the dry spring of 1988 the average gross B&C score was 121 inches. However, during the wet spring of 1992, the average B&C score was 141 inches.
"Spring rain alone accounted for as much as a 20-inch shift in gross B&C score for mature bucks," said Hellickson, "and spring rain explained 70 percent of the year to year variability in antler size."
On the South Texas buck project, researchers also found a high correlation between spring rainfall, March through May, and the number of 160 inch or bigger bucks harvested the following fall on the King Ranch. Given that, for those interested in trophy buck management, Hellickson recommended harvesting bucks at 5.5 years of age during a wet spring for the simple reason that the chances of getting two good years in a row are slim and therefore antlers are not likely to be better the next year. When spring rainfall is normal or below normal, Hellickson recommended delaying harvest until bucks are at least 7.5 years of age.
The next question, are spikes inferior, is a question that is old as — well, it’s old. It’s certainly been debated for decades, and it’s still being debated.
To answer this question, Hellickson again turned to data collected from the South Texas buck capture study. Researchers calculated the average gross B&C score of yearling bucks with two to three antler points versus the average gross B&C score for yearling bucks with four or more antler points when those bucks were recaptured at 2.5, 3.5, 4.5 on out to 7.5 years of age.
In every age class, the bucks that were forked antlered as yearlings outscored the bucks that were spikes as yearlings. In the 4.5 age category the gross B&C score of the bucks that were spikes as yearlings ranged from 85 inches to 145 inches, with the average being 116 inches. However, the gross B&C score of the bucks that were forked as yearlings when recaptured at age 4.5 ranged from 90 to 160 with an average of 130. Looking at the data another way, 11 of the 15 bucks that had a gross B&C score under 110 were spikes as yearlings, Hellickson said, and 12 of the 13 bucks scoring above 140 were forked antlered yearlings.
In the 5.5 age category, the bucks that were spikes as yearlings had an average gross B&C score of 125 while the forked antlered yearlings at 5.5 years of age had an average B&C score of 144, though one buck scored 210 inches. Looking at the same data another way, 13 of the 16 lowest scoring 5.5 year-old bucks were spikes as yearlings while nine of the 10 highest scoring bucks at 5.5 years of age were forked antlered yearlings.
They also compared spike yearling antlers to yearling bucks with six or more antler points at the various age classifications. In the 5.5 years or older category, researchers never captured a buck that was a spike as a yearling that grossed above 160. In fact, Hellickson noted that two-thirds of the bucks that were spikes as yearlings never broke 130 at maturity. However, only 18 percent of the yearling bucks with six or more antlered points failed to break 130 at maturity and 36 percent of the yearling bucks with six or more points broke 160 at maturity.
"So are spikes inferior? Based on our data set, we say yes. These data show that yearling antler size is a good predictor of antler size at maturity."
He added that all bucks that were spikes as yearlings were grouped together. In other words, they did not try to determine if the bucks were spikes as yearlings for nutritional reasons or for genetic reasons.
"In my opinion, it doesn’t matter whether a buck is a spike for nutritional reasons or for genetic reasons," Hellickson stated. "I say that because in this study, in every case, spikes were inferior to the forked group.
"A few spikes raised in pens have turned into big deer at maturity, but it’s rare," he continued. "But, in the wild, in this study we never had a buck that was a spike as a yearling gross score above 155," he reiterated. "I think biologists should never let the exception be misconstrued to be the rule when it comes to spike buck harvest."
As for the third question, the South Texas buck capture project also provided researchers with some good data that enabled them to develop definitive culling criteria for landowners to use. To do this they compared the number of points and the gross B&C scores of the bucks that were recaptured at various stages of their life.
Researchers captured 16, 3.5 year-old bucks with seven or fewer antler points that were recaptured at age 5.5 or older. One of those 16, Hellickson said, had a gross B&C score above 140 at maturity, but none of the 3.5 year-old bucks with seven or fewer antler points that were recaptured as mature bucks broke 150.
They also captured 41, 3.5 year-old bucks that had eight antler points. Two of the 41 had a gross B&C score above 150 at maturity and one grossed above 160 at maturity.
There were 13, 3.5 year-old bucks with nine points. Two out of the 13 grossed above 150 at maturity and one grossed above 160.
Additionally, researchers captured 40, 3.5 year-old bucks with 10 or more antler points. When these bucks were recaptured at 5.5 years of age or older, seven out of 40 broke 160 and 15 out of 40 broke 150.
"The odds were a lot higher that a 3.5 year-old buck with 10 or more points would break 150 or 160 compared to a 3.5 year-old buck with seven or fewer points," Hellickson explained.
For bucks in the 4.5 age category, researchers followed the same protocol. Over the course of the study, 85 bucks captured at 4.5 year of age had eight points or fewer. When those bucks were recaptured at 5.5 years of age or older, none of them grossed over 150.
"That tells me that it’s pretty safe to cull bucks that have eight or fewer points at 4.5 years of age," Hellickson told listeners, "because those bucks are not likely to gross over 150 at maturity."
They also captured 35, 4.5 year-old bucks with nine points that they were able to recapture at 5.5 years of age or older. Two of the 35 ended up above 150; one out of 35 (three percent) ended up above 160, Hellickson said.
Additionally, 75 bucks captured at 4.5 years of age had 10 or more points. Of those 75 bucks recaptured at maturity, 20 grossed over 150 while eight of the 75 grossed above 160.
Hellickson became the wildlife biologist for the King Ranch in 1998, a position he held for 12 years. He used data from the South Texas buck capture project to develop a culling strategy for the King Ranch. The culling categories which were designed and implemented beginning in the fall of 2001 were as follows: any buck with at least one unbranched antler, any buck 3.5 years of age or older with seven or fewer total antler points, any buck 4.5 years of age or older with eight or fewer total antler points, and any buck 5.5 years of age or older with gross B&C score less than 130. Any buck that did not fall into one of those four categories qualified as a trophy.
After implementing the non-quota cull buck categories, the buck harvest on the King Ranch increased dramatically while the harvest of trophy bucks declined. In fact, before the culling criteria were implemented, only about 24 percent of the bucks harvested on the King Ranch qualified as culls. After the culling program was implemented, 87 percent qualified as culls.
He showed a graph of the percentage of trophy bucks, those that grossed over 160, harvested on the King Ranch from 1998 to 2008. In 1998, five percent of the trophy bucks grossed above 160. In 2008 that number had increased to 22 percent.
"You might think, ‘Wow, the culling program really worked; bucks got bigger over time,’ but I don’t think that’s the case here," Hellickson opined. "Instead, what happened is we reduced the trophy buck quota so the hunters became more selective in what they shot as trophy bucks. And because of the increased selection, a higher percentage of the trophy bucks killed gross scored above 160."
What the culling program really did, he told listeners, is provide for a lot more hunter recreation.
"We forced hunters to shoot fewer trophy bucks, but we gave them a lot more flexibility in harvesting cull and management type bucks."
Hellickson also told listeners that the culling criteria he implemented on the King Ranch could be considered "pretty conservative" for a South Texas ranch. On ranches that employ a more intensive management program, he suggested shifting the bar up a notch and culling yearling bucks with five or fewer points, 3.5 year-old bucks with eight or fewer points, 4.5 year-old bucks with nine or fewer points and, depending on harvest goals, perhaps consider culling 5.5 year-old bucks that gross score under 150.
So does culling work? To address this question, Hellickson turned to data gathered from the King Ranch culling study, which was being conducted simultaneously with the South Texas buck capture study. The culling criteria were established by TPWD based on results of penned studies from the Kerr Wildlife Management Area. The study was conducted on a 10,000-acre portion of the King Ranch. An adjacent 10,000 acres was designated as the control.
On the control area only five culls were removed over the course of the seven-year study. On the treatment area from 1999 to 2005 researchers removed 158 culls through gun harvest using culling criteria established by Texas Parks and Wildlife. That criteria included every yearling buck with fewer than six antler points and every 2.5 year-old or older buck with eight or fewer antler points, Hellickson said.
He showed a picture of a 2.5 year-old buck with a double drop tine that gross scored 128 captured on the treatment area during the first year of the study. That buck remained on the treatment area for the next five years while 125 inferior bucks were harvested from his neighborhood.
During the second year of the study the buck with the two drop tines was recaptured. At that time he had 17 points and gross scored 161. The following year he grossed 178; at age 5.5 he grossed 199. The buck was harvested the following year at 6.5 years of age. He grossed 190. The point Hellickson was making was that this particular buck offered researchers the perfect scenario to test their hypotheses.
Researchers kept track of the percentage of bucks captured by helicopter net gun on the two areas that still qualified as culls after the culling program was initiated.
"On the treatment area where we were selectively harvesting and removing all cull bucks you would expect the percentage of cull bucks captured at random to decline over time," Hellickson said. "However, after seven years of intensive culling, the percentage of bucks qualifying as culls on the two areas didn’t change. In fact, in the final year of harvest, 61 percent of the bucks captured at random on the treatment area qualified as culls and 61 percent captured at random on the control qualified as culls. We didn’t see any shift in the percentage of cull bucks between the two areas," Hellickson told listeners.
Additionally, at the end of the culling period they found no difference in the average gross B&C score of bucks on the treatment area versus the control.
Why, then, didn’t the culling program work on the 10,000-acre treatment area? One potential reason, Hellickson said, is that the culling criteria were less than ideal. Another potential problem, he said, was that the culling program was not flexible from year to year. For example, culling criteria did not change during a dry year versus a wet year. Additionally, both the treatment area and the control were low-fenced. Thus, researchers had a problem with bucks dispersing either from the treatment area to the control or vice versa.
They also found that some of the individual bucks that were recaptured multiple times changed their status as to whether or not they were considered culls. For example, during a wet year a buck had nine points, but if that same buck was recaptured later during a dry year, he might be considered a cull.
Still another possible explanation is that culling mistakes are made when gun harvest is employed.
"One of the worst mistakes one can make is to shoot a yearling buck that was mistaken for a seven point 2.5 year-old buck," Hellickson told listeners. "That’s why I don’t like culling the 2.5 year-old age class. Oftentimes the biggest yearlings look like small two year-olds and you don’t want to be shooting your biggest yearling bucks. Those are your future 160 or better bucks."
The final possible contributing factor as to why the culling study didn’t work has to do with individual buck breeding success. In an intensive DNA study, Dr. Randy DeYoung found that no matter the age or the size of the bucks, on average, bucks are only going to sire 1.5 fawns per year.
"So the very low buck breeding success likely contributed to the lack of results from the culling program."
To put the results in perspective he used what has become known as the "corral continuum" coined by Faith ranch owner Stuart Stedman. The idea is that the closer one moves toward a deer pen situation the more likely a culling program has a chance of success. The closer one moves to a free ranging, large acreage setting the less likely culling will be effective.
"On the King Ranch study we removed 43 percent of the culls that were available for harvest. We were only able to get eight percent of the culls removed before the breeding season. However, at the Kerr Wildlife Management Area deer pens, researchers removed 70 to 85 percent of the cull bucks annually and all were removed prior to the rut. In the latter case the pen data showed a huge improvement in antler size through selective breeding," commented Hellickson.
"That’s a very difficult thing to do on a ranch that’s very large," he continued, "because you’re talking about killing a whole lot of animals and doing it without making any mistakes and doing it all before the breeding season.
"The bottom line, then, is if you expect to see genetic change through culling, if you expect to see the kind of results that TPWD saw with their pen data, you have to have a small property and it must be high fenced. Those two things are mandatory," Hellickson opined.
Wrapping up, Hellickson reiterated that culling, in this particular study, did not increase antler size. Culling does, however, increase the opportunity for recreation, and increased recreational opportunity may translate into increased revenue. Additionally, in areas where deer density is at or near the maximum that the habitat will support, removing cull deer should have a positive nutritional effect on the remaining deer and that positive effect may translate into larger antlered bucks.
Finally, Hellickson said a culling program greatly reduces any chance of high grading.
"I think culling helps a lot to offset what we’ve done for decades, which was only harvest the biggest bucks we could find each year," he concluded.
In the Q&A Hellickson was asked to offer thoughts on doe harvest, and whether it was better to cull young does or mature does.
"My quick and short answer is if it’s an adult doe, shoot it," Hellickson responded. "I’ve heard a couple of opposing theories about the class of doe to target for harvest. My theory is if you have a high deer density and you need to remove deer, don’t worry about the age of the doe," he continued. "It’s difficult to age a doe on the hoof. You can tell the younger aged does, but telling a 2.5 year-old doe from a four or five year-old doe is difficult."
He was asked to expound on culling spikes in a dry versus a wet year. Though the South Texas buck capture project did not address this particular issue, Hellickson told listeners that it makes sense during a drouth year to slack off spike buck harvest because a large percentage, perhaps as many as 60 to 70 percent of the yearling bucks during a severe drouth, could be spikes. However, he added, such a decision is really ranch or manager-specific depending on one’s goals.
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