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Article in Deer & Deer Hunting Magazine
The Facts and Truth About Culling Bucks
By: By John Ozoga
Culling is the selective removal of presumably inferior deer in order to improve the quality of the remaining population. Among whitetails, the culling harvest strategy generally involves targeting those bucks with inferior antlers for removal to improve overall antler quality of those left to do the breeding and for harvest at an older age.
In recent years, it seems hunters have become fanatical in their quest to kill monster bucks carrying trophy-sized antlers — at any cost.
The practice of culling bucks with small antlers as a management strategy originated in Texas during the 1980s. Presumed benefits of such harvesting were based upon penned deer research. These early studies indicated that removal of spike-antlered yearling bucks not only improved antler quality, but also improved inherent genetic traits for large antlers.
However, later studies challenged these findings. While conducting controlled breeding studies of deer from Northern as well as Southern regions, Mississippi researchers found no evidence that removal of yearling bucks with spike or few antler points improved antler quality. Instead, they argued that a yearling buck’s antlers were more influenced by birth date and nutrition than genetics.
Until recently, the culling debate has revolved primarily around studies using captive deer, held in unnaturally high densities and fed either high-quality or restricted diets. Such controversy now seems to surface at any regional meeting among hunters and wildlife professionals.
The Culling Debate
Study results on captive deer have produced recommendations ranging from removing all spike-antlered bucks (primarily yearlings) to complete protection of all yearling bucks regard- less of their antler traits.
Those favoring culling claim spike-antlered young bucks are genetically inferior, will never attain quality antlers typical of fork-antlered yearlings even when mature, and will contribute to perpetuation of such undesirable traits. In addition, they claim culling will help reduce deer density, thereby improv- ing herd nutrition, as well as remove small-antlered genes from the herd and improve future antler quality.
For example, research conducted by Mitchell Lockwood and his cohorts from the Texas Parks and Wildlife Department, indicated selective breeding by superior-antlered yearling bucks improves subsequent yearling antler scores. Lockwood and his group concluded the following: “Our findings clearly indicate that under constant suboptimal environmental conditions, phenotypic change in antler quality can be realized with intensive selective harvest of yearling males.”
Conversely, Harry Jacobson argues little or no improvement in future antler quality will result by culling based on yearling antler traits. Jacobson and Texas A&M geneticist Steven Lukefahr based their conclusions on the examination of 220 yearling bucks raised at research facilities in Mississippi. They found that the doe’s nurturing ability was far more important than genetics in determining the yearling buck’s antler points, spread, weight and beam length.
Although there have been relatively few studies conducted to evaluate the effects of culling on antler quality among free-ranging whitetails, findings from field studies tend to fuel the culling debate.
High-grading
In Mississippi, research headed up by Bronson Strickland found that protection of small-antlered young males — intended to more closely balance adult sex ratios — might inadvertently contribute to smaller than normal antlers in subsequent years in some areas.
More specifically, these researchers discovered that implementation of a 4-point minimum harvest rule resulted in a reduction in average antler size among 2.5- and 3.5-year-old bucks in subsequent years on certain areas. Hence, although the strategy may have increased the proportion of older bucks in the population, overall antler quality declined.
This unintended (high-grading) result added fuel to the culling controversy. However, it is important to recognize that antler genetics were not impacted in the process. Instead, antler size was smaller because of harvest restrictions that protected deer born late in the season. At the same time, many early born bucks grew 4-point or better antlers, hence they were eligible for harvest.
Smaller antlers in older bucks more likely can be explained by excessive harvest of young bucks with the largest antlers when they were yearlings.
It’s important to recognize that some bucks might have larger antlers than others at yearling age for many various reasons, such as being born early, being a single fawn raised by a maternally experienced doe, being disease free, or having been raised in exceptionally good habitat.
In the above-mentioned Mississippi study, investigators also found that results of the 4-point harvest strategy differed among the three regions studied. That is, antler quality among 2.5- and 3.5-year-old bucks declined only in the most fertile soil region after implementation of the 4-point harvest rule. They speculate that this could have occurred for two reasons: (1) inherent regional differences in soil fertility and (2) differences in the buck harvest intensity.
In the fertile Delta region, yearling antler development was not limited by forage quality and males expressed their potential for antler size. Therefore, given the 4-point harvest strategy, a large percent of the yearling cohorts could legally be harvested.
By comparison, relatively poor soils in the Upper and Lower Coastal Plain might have resulted in later fawn- ing dates as well as poorer physical (and antler) development. Given the environmental constraints, relatively few yearling bucks were legal targets.
According to the researchers, this could have resulted in “random” removal of yearlings and no decrease in cohort antler size in subsequent years.
The researchers suggest that deer in the rich-soil Delta region might have experienced high harvest rates (75 percent or more) of vulnerable males, which caused differences in antler size for pre- and post-regulation cohorts. Conversely, populations in the Upper and Lower Plain regions might have experienced low harvest rates, which yielded no effect. The best data indicate that yearling harvest rates of less than 50 percent are not likely to impact subsequent cohort antler char- acteristics.
Strickland and his group concluded the following: “Selective-harvest criteria (SHC) that protect small-antlered young bucks coupled with high harvest rates of young vulnerable males may negatively impact cohort antler size in subsequent years on some areas. Use of SHC that protects young males with small antlers should be viewed as a temporary solution to chronic age- structure problems.”
Antler Growth Patterns
Although their findings have been challenged, studies conducted by Ben Koreth and James Kroll in Texas showed that a white-tailed buck’s first set of antlers was a poor predictor of antler growth at maturity in wild deer populations. In other words, according to the authors, selective removal of small-antlered yearling bucks will not increase overall mature buck antler size.
Koerth and Kroll conducted their study on 12 ranches in Texas ranging from 2 to 23 square miles in size (11 of which were fenced), some of which employed supplemental feeding. Initially, they captured and marked male fawns and yearlings. In subsequent years, they attempted to recapture and examine as many of the marked animals as possible.
Yearling bucks were divided into two antler-point categories, those with 3 or fewer antler points and those with 4 or more antler points. Then, the researchers compared recaptured bucks in the two antler-point categories to determine differences in antler growth at 2.5 years, 3.5 years, 4.5 years and 5.5 or more years in age.
Bucks that started out with 3 or less antler points remained smaller in all measured antler traits at 2.5 years of age and in most antler traits at 3.5 years of age. However, by 4.5 years of age there were no differences in any antler measurements regardless of their year- ling antler-point category.
Although antler measurements increased for all males as they matured, small-antlered yearlings added antler mass at a faster rate in succeeding years, as compared to large-antlered yearlings. This resulted in no difference in antler size, regardless of their yearling antler size, by the time bucks grew their fourth set of antlers when 4.5-years-old.
Koreth and Kroll theorize there are different antler growth patterns in white-tailed bucks. One pattern is a high rate of antler growth for the first few years, followed by a slower rate each year thereafter. Another pattern is steady (incremental) growth throughout the productive life of the animal. A third pattern is slow antler growth at first, followed by an increased growth rate at some point in the animal’s life.
Theoretically, all three patterns end with roughly the same antler score at maturity. Hence, in their view, yearling antlers do not serve as a reliable predictor of antler growth potential, meaning selective removal of yearling bucks with small antlers is not likely to improve overall mature buck antler quality.
Some researchers have openly criticized the study by Koerth and Kroll, claiming methodology and data analy- sis were flawed and biased conclusions. Steve Demarias and Brian Strickland, in particular, have questioned the effect of culling small-antlered deer, failure to include study site as a random effect in their analysis, and for not using a repeated measures analysis structure.
The Latest
The latest findings by David Hewitt and a group of Texas A&M researchers might have finally answered this rather intriguing question: Do yearling antlers serve as a predictor of antler growth potential? These researchers used capture and harvest records from an impressive sample of 2,940 male white- tails on five study sites in Texas over a 10-year period to track antler development among bucks from yearling age to 5 years of age.
In their study, yearling deer with 3 or fewer antler points had antlers at maturity that were 32 centimeters smaller (on the Boone and Crockett scale) than deer with 4 or more antler points at yearling age.
According to Hewitt and his cohorts: “Our data show clearly that yearling male deer with small antlers have, on average, smaller antlers at maturity.” In their view, “The correlation between yearling and mature antler size was unequivocal.”
As expected, this latest study found that yearling body size was positively related to yearling antler size. This suggests that yearling deer with small antlers might have experienced poor nutrition early in life. However, the relationship between yearling antler size and body size became weaker at older age. As a result, this suggests that deer have some compensatory growth capability in body size or that factors other than early life nutrition have a greater influence on body size in older deer.
Since whitetails exhibit segregation of the adult sexes, this also implies that habitat designed to favor one sex might not necessarily favor the other. Obviously, nutritional conditions on the fawns natal range are critically impor- tant, as growth and development at a young age will impact the deer’s devel- opment throughout life. This does not mean antler genetics are unimportant. But this is a complex subject deserving far more discussion than allowed here.
Given their study findings, the authors concluded the following: “Because of a positive relationship between yearling and mature antler size, selective harvest of juvenile males can either increase or decrease the aver- age antler size of the cohort, depending upon harvest criteria.”
Management Implications
Personally, I don’t know if the research reported by Hewitt and his group will put an end to the yearling buck culling debate. I’ll reserve final judgment until I see a study of comparable proportions conducted on Northern whitetail range (which is highly unlikely in the near future), where fluctuating environmental pressures differ from those experienced on Southern range.
Meanwhile, I agree with the Hewitt et al. appraisal, as follows: “Managers using only antler size as a harvest criterion to protect young deer should recognize the potential to harvest young deer with large antlers, a harvest strategy that could increase the number of deer reaching older age classes but that may cause a decline in average antler size as the cohort ages. Conversely, selective harvest of the smallest male deer in a cohort may reduce the total number of deer reaching older age classes, but the average antler size of the cohort will be larger and, because of reduced resource competition, remaining deer may have improved growth and survival. Finally, antler size increases with age and therefore, managers seeking to harvest male deer with large antlers should delay harvest until deer are 5 or more years of age.”
The Facts and Truth About Culling Bucks
By: By John Ozoga
Culling is the selective removal of presumably inferior deer in order to improve the quality of the remaining population. Among whitetails, the culling harvest strategy generally involves targeting those bucks with inferior antlers for removal to improve overall antler quality of those left to do the breeding and for harvest at an older age.
In recent years, it seems hunters have become fanatical in their quest to kill monster bucks carrying trophy-sized antlers — at any cost.
The practice of culling bucks with small antlers as a management strategy originated in Texas during the 1980s. Presumed benefits of such harvesting were based upon penned deer research. These early studies indicated that removal of spike-antlered yearling bucks not only improved antler quality, but also improved inherent genetic traits for large antlers.
However, later studies challenged these findings. While conducting controlled breeding studies of deer from Northern as well as Southern regions, Mississippi researchers found no evidence that removal of yearling bucks with spike or few antler points improved antler quality. Instead, they argued that a yearling buck’s antlers were more influenced by birth date and nutrition than genetics.
Until recently, the culling debate has revolved primarily around studies using captive deer, held in unnaturally high densities and fed either high-quality or restricted diets. Such controversy now seems to surface at any regional meeting among hunters and wildlife professionals.
The Culling Debate
Study results on captive deer have produced recommendations ranging from removing all spike-antlered bucks (primarily yearlings) to complete protection of all yearling bucks regard- less of their antler traits.
Those favoring culling claim spike-antlered young bucks are genetically inferior, will never attain quality antlers typical of fork-antlered yearlings even when mature, and will contribute to perpetuation of such undesirable traits. In addition, they claim culling will help reduce deer density, thereby improv- ing herd nutrition, as well as remove small-antlered genes from the herd and improve future antler quality.
For example, research conducted by Mitchell Lockwood and his cohorts from the Texas Parks and Wildlife Department, indicated selective breeding by superior-antlered yearling bucks improves subsequent yearling antler scores. Lockwood and his group concluded the following: “Our findings clearly indicate that under constant suboptimal environmental conditions, phenotypic change in antler quality can be realized with intensive selective harvest of yearling males.”
Conversely, Harry Jacobson argues little or no improvement in future antler quality will result by culling based on yearling antler traits. Jacobson and Texas A&M geneticist Steven Lukefahr based their conclusions on the examination of 220 yearling bucks raised at research facilities in Mississippi. They found that the doe’s nurturing ability was far more important than genetics in determining the yearling buck’s antler points, spread, weight and beam length.
Although there have been relatively few studies conducted to evaluate the effects of culling on antler quality among free-ranging whitetails, findings from field studies tend to fuel the culling debate.
High-grading
In Mississippi, research headed up by Bronson Strickland found that protection of small-antlered young males — intended to more closely balance adult sex ratios — might inadvertently contribute to smaller than normal antlers in subsequent years in some areas.
More specifically, these researchers discovered that implementation of a 4-point minimum harvest rule resulted in a reduction in average antler size among 2.5- and 3.5-year-old bucks in subsequent years on certain areas. Hence, although the strategy may have increased the proportion of older bucks in the population, overall antler quality declined.
This unintended (high-grading) result added fuel to the culling controversy. However, it is important to recognize that antler genetics were not impacted in the process. Instead, antler size was smaller because of harvest restrictions that protected deer born late in the season. At the same time, many early born bucks grew 4-point or better antlers, hence they were eligible for harvest.
Smaller antlers in older bucks more likely can be explained by excessive harvest of young bucks with the largest antlers when they were yearlings.
It’s important to recognize that some bucks might have larger antlers than others at yearling age for many various reasons, such as being born early, being a single fawn raised by a maternally experienced doe, being disease free, or having been raised in exceptionally good habitat.
In the above-mentioned Mississippi study, investigators also found that results of the 4-point harvest strategy differed among the three regions studied. That is, antler quality among 2.5- and 3.5-year-old bucks declined only in the most fertile soil region after implementation of the 4-point harvest rule. They speculate that this could have occurred for two reasons: (1) inherent regional differences in soil fertility and (2) differences in the buck harvest intensity.
In the fertile Delta region, yearling antler development was not limited by forage quality and males expressed their potential for antler size. Therefore, given the 4-point harvest strategy, a large percent of the yearling cohorts could legally be harvested.
By comparison, relatively poor soils in the Upper and Lower Coastal Plain might have resulted in later fawn- ing dates as well as poorer physical (and antler) development. Given the environmental constraints, relatively few yearling bucks were legal targets.
According to the researchers, this could have resulted in “random” removal of yearlings and no decrease in cohort antler size in subsequent years.
The researchers suggest that deer in the rich-soil Delta region might have experienced high harvest rates (75 percent or more) of vulnerable males, which caused differences in antler size for pre- and post-regulation cohorts. Conversely, populations in the Upper and Lower Plain regions might have experienced low harvest rates, which yielded no effect. The best data indicate that yearling harvest rates of less than 50 percent are not likely to impact subsequent cohort antler char- acteristics.
Strickland and his group concluded the following: “Selective-harvest criteria (SHC) that protect small-antlered young bucks coupled with high harvest rates of young vulnerable males may negatively impact cohort antler size in subsequent years on some areas. Use of SHC that protects young males with small antlers should be viewed as a temporary solution to chronic age- structure problems.”
Antler Growth Patterns
Although their findings have been challenged, studies conducted by Ben Koreth and James Kroll in Texas showed that a white-tailed buck’s first set of antlers was a poor predictor of antler growth at maturity in wild deer populations. In other words, according to the authors, selective removal of small-antlered yearling bucks will not increase overall mature buck antler size.
Koerth and Kroll conducted their study on 12 ranches in Texas ranging from 2 to 23 square miles in size (11 of which were fenced), some of which employed supplemental feeding. Initially, they captured and marked male fawns and yearlings. In subsequent years, they attempted to recapture and examine as many of the marked animals as possible.
Yearling bucks were divided into two antler-point categories, those with 3 or fewer antler points and those with 4 or more antler points. Then, the researchers compared recaptured bucks in the two antler-point categories to determine differences in antler growth at 2.5 years, 3.5 years, 4.5 years and 5.5 or more years in age.
Bucks that started out with 3 or less antler points remained smaller in all measured antler traits at 2.5 years of age and in most antler traits at 3.5 years of age. However, by 4.5 years of age there were no differences in any antler measurements regardless of their year- ling antler-point category.
Although antler measurements increased for all males as they matured, small-antlered yearlings added antler mass at a faster rate in succeeding years, as compared to large-antlered yearlings. This resulted in no difference in antler size, regardless of their yearling antler size, by the time bucks grew their fourth set of antlers when 4.5-years-old.
Koreth and Kroll theorize there are different antler growth patterns in white-tailed bucks. One pattern is a high rate of antler growth for the first few years, followed by a slower rate each year thereafter. Another pattern is steady (incremental) growth throughout the productive life of the animal. A third pattern is slow antler growth at first, followed by an increased growth rate at some point in the animal’s life.
Theoretically, all three patterns end with roughly the same antler score at maturity. Hence, in their view, yearling antlers do not serve as a reliable predictor of antler growth potential, meaning selective removal of yearling bucks with small antlers is not likely to improve overall mature buck antler quality.
Some researchers have openly criticized the study by Koerth and Kroll, claiming methodology and data analy- sis were flawed and biased conclusions. Steve Demarias and Brian Strickland, in particular, have questioned the effect of culling small-antlered deer, failure to include study site as a random effect in their analysis, and for not using a repeated measures analysis structure.
The Latest
The latest findings by David Hewitt and a group of Texas A&M researchers might have finally answered this rather intriguing question: Do yearling antlers serve as a predictor of antler growth potential? These researchers used capture and harvest records from an impressive sample of 2,940 male white- tails on five study sites in Texas over a 10-year period to track antler development among bucks from yearling age to 5 years of age.
In their study, yearling deer with 3 or fewer antler points had antlers at maturity that were 32 centimeters smaller (on the Boone and Crockett scale) than deer with 4 or more antler points at yearling age.
According to Hewitt and his cohorts: “Our data show clearly that yearling male deer with small antlers have, on average, smaller antlers at maturity.” In their view, “The correlation between yearling and mature antler size was unequivocal.”
As expected, this latest study found that yearling body size was positively related to yearling antler size. This suggests that yearling deer with small antlers might have experienced poor nutrition early in life. However, the relationship between yearling antler size and body size became weaker at older age. As a result, this suggests that deer have some compensatory growth capability in body size or that factors other than early life nutrition have a greater influence on body size in older deer.
Since whitetails exhibit segregation of the adult sexes, this also implies that habitat designed to favor one sex might not necessarily favor the other. Obviously, nutritional conditions on the fawns natal range are critically impor- tant, as growth and development at a young age will impact the deer’s devel- opment throughout life. This does not mean antler genetics are unimportant. But this is a complex subject deserving far more discussion than allowed here.
Given their study findings, the authors concluded the following: “Because of a positive relationship between yearling and mature antler size, selective harvest of juvenile males can either increase or decrease the aver- age antler size of the cohort, depending upon harvest criteria.”
Management Implications
Personally, I don’t know if the research reported by Hewitt and his group will put an end to the yearling buck culling debate. I’ll reserve final judgment until I see a study of comparable proportions conducted on Northern whitetail range (which is highly unlikely in the near future), where fluctuating environmental pressures differ from those experienced on Southern range.
Meanwhile, I agree with the Hewitt et al. appraisal, as follows: “Managers using only antler size as a harvest criterion to protect young deer should recognize the potential to harvest young deer with large antlers, a harvest strategy that could increase the number of deer reaching older age classes but that may cause a decline in average antler size as the cohort ages. Conversely, selective harvest of the smallest male deer in a cohort may reduce the total number of deer reaching older age classes, but the average antler size of the cohort will be larger and, because of reduced resource competition, remaining deer may have improved growth and survival. Finally, antler size increases with age and therefore, managers seeking to harvest male deer with large antlers should delay harvest until deer are 5 or more years of age.”