Caesar Kleberg Wildlife Research Institute

Project Participants
David G. Hewitt, Randy W. DeYoung, Charles DeYoung, Tim Fulbright, Fred Bryant, Mickey Hellickson, Ken Gee, Karl V. Miller, TPWD, QDMA, NRCS

Students
Aaron Foley, John Lewis, Evan McCoy, Jason Sumners, Dean Wiemers

In 1998, the Deer Research Program at the Institute initiated a project with the objective of evaluating a culling strategy that attempted to increase antler size in white-tailed deer by removing bucks with small antlers.  This project involved the capture of bucks in treatment and control pastures on the King Ranch.  During this time, the King Ranch site was added to the South Texas Buck Capture Project, increasing that project’s ability to assess factors affecting deer antler size and refine deer aging techniques.  As a result, researchers have been able to conduct several other projects on the King Ranch, including, survival and dispersal of yearling bucks, survival and movements of trap, transport, and transplant (TTT) deer, factors affecting habitat use of deer, factors influencing buck breeding success, and breeding behavior of male and female deer relative to age class.

To date, 4 graduate students under the direction of 5 deer research scientists from the Institute collaborate with King Ranch biologists to determine which research projects are relevant to the needs of wildlife managers today.  Additionally, the Institute and King Ranch cooperate with Texas Parks and Wildlife Department, Quality Deer Management, and USDA – Natural Resource Conservation Service.

Progress Reports

Completed Research

Molecular Evaluation of the White-tailed Deer (Odocoileus virginianus) Mating System
Randy W. DeYoung, Stephen Demarais, Kenneth L. Gee, Rodney L. Honeycutt, Mickey W. Hellickson, and Robert A. Gonzales

We used genetic-based paternity assignments from 3 diverse populations of white-tailed deer (Odocoileus virginianus) to evaluate the long-held assumption that male reproductive success in this species is highly skewed toward a small number of mature, dominant individuals. The study populations represented a range of adult sex ratios and male age structures. Male reproductive success was distributed among a large number of males in all populations, with no evidence for highly skewed access to mating for any individual male. Surprisingly, physically immature males (1.5 and 2.5 years of age) collectively fathered 30–33% of offspring in all populations, even where mature males were present. Ecological and behavioral variables appear to constrain the ability of individual males to monopolize access to females, resulting in a wider distribution of reproductive success than expected based on previous ecological and behavioral studies of white-tailed deer. Qualitative differences in the distribution of male reproductive success among study sites suggested that demographic attributes such as adult sex ratio and male age structure might influence the degree of competition for mates. Further study incorporating known-age cohorts or integrating movements and behavior is necessary for understanding the affects of population demographics as well as the physical and behavioral attributes that confer reproductive success in diverse populations of white-tailed deer.

Survival and Movement of TTT Deer
(published in Southeastern Association of Fish and Wildlife Agencies)
Aaron M. Foley, David G. Hewitt, Randy W. DeYoung, Karl V. Miller, Mick W. Hellickson, Scott Mitchell, Mitch A. Lockwood, and Brent Pierce

In south Texas, white-tailed deer (Odocoileus virginianus) translocations have become a common technique for non-lethal means of deer removal with the recent implementation of a Trap, Transport, and Transplant (TTT) permit program.  However, the effectiveness of TTT as a management tool has not been evaluated.  We monitored survival, movements, and body condition of 49 white-tailed deer from 2 translocations on 2 2,000-ha south Texas properties, 1 of which was partially enclosed by a 2.5-m net-wire fence.  Annual survival was lower in the partially fenced property (63%) compared to the unfenced property (74%), but overall survival was similar to survival rates of native south Texas deer reported in previous studies (ca. 71-72%).  As expected, more deer left the unfenced property (60%) than the partially enclosed property (15%).  Cumulatively, 41% of deer survived and remained on the release area after 1 year.  Young (1.5-3.5 years old) translocated males had below average antler gain, body condition scores and rump fat measurements 6-8 months post-release compared to resident males.  Results of this study indicate that reasonable survival rates can be achieved, but released deer may not remain in the vicinity of the release site and tend to have below-average body condition 6-8 months after release compared to native deer.  The results of this study provide managers a basis for evaluating translocations as a tool to achieve management goals.

Dispersal by Yearling Male White-tailed Deer and Implications for Management
(published in the Journal of Wildlife Management)
J. Evan McCoy, David G. Hewitt, and Fred C. Bryant

The scale at which populations use the landscape influences ecological processes and management decisions.Dispersal and home-range size define the scale of landscape use for many large-mammal species. We measured dispersal and home-range size of yearling male white-tailed deer (Odocoileus virginianus) in southern Texas,and compared our results to values from the literature to understand the implications of dispersal in management of deer populations. We used radiotelemetry to monitor 22 yearling deer on one study site from October 1998 to October 1999, and 27 yearling deer on a second study site from October 1999 to October 2000. On the 2 study sites,68% and 44% of yearling deer established new areas of use 4.4 ± 1.0 km and 8.2 ± 4.3 km, respectively, from the center of their autumn home range. Yearling males with spike antlers (2 points) were less likely to disperse than yearlings with fork antlers (>2 points) on 1 study site. Computer simulation showed that the scale at which deer use the landscape is large compared to property sizes in southern Texas and probably in other areas of the white-tailed deer’s range. Differences in scale between land ownership patterns and landscape use by deer may result in a failure to meet management objectives and conflict among managers. High harvest rates for male deer occur in part because deer movements are large relative to property size, creating a “tragedy of the commons.” Cooperative management groups are beneficial if all landowners in an area agree on management objectives. Otherwise,deerproof fences often are erected to reduce conflicts among property owners.

Breeding Behavior of Male and Female White-tailed Deer Relative to Age Class
 Jason A. Sumners, Randy W. DeYoung, Rodney L. Honeycutt, Stephen Demarais, Mickey W. Hellickson, Kenneth L. Gee, and Robert A. Gonzales

Although the breeding system of white-tailed deer is commonly described as a dominance-based hierarchy, recent studies have documented the breeding success of all age classes of bucks in white-tailed deer. It has been suggested that the breeding success of young bucks is the result of exclusively mating with young does, while older bucks concentrate their efforts on mature does, presumably because these does are more experienced and more likely to recruit one or more fawns. Additionally, older does may not tolerate mating attempts of younger bucks, preferring to mate with dominant bucks. The occurrence of multiple paternity in many white-tailed deer populations indicates that female choice may play an important role in determining the distribution of buck breeding success.

We are sampling litters of fawns and assigning paternity using a panel of genetic markers. Our preliminary results indicate that yearling bucks successfully mate with does of all ages. The mean age of female mates was 5.1, 4.8, and 5.0 for 1.5, 2.5, and 3.5+ year-old bucks, respectively. Additionally, we documented 2 incidents of multiple paternity involving yearling bucks.

The breeding success of young bucks may be restricted to the peak of the breeding season when the most does are in estrous and mature bucks cannot monopolize access to all does. The lack of an association between buck age and doe age is more evidence that overall male-to-male competition may not play an important role in gaining access to does. This ongoing research should provide further insights into breeding behavior and success of while-tailed deer.

In Progress

Factors Influencing Male White-tailed Deer Breeding Success (preliminary)
Aaron M. Foley, Randy W. DeYoung, David G. Hewitt, Mick A. Hellickson, Karl V. Miller and Ken Gee

Previous studies have made it clear that it is difficult to predict which male white-tailed deer are breeding.  One way to better understand which males may be successfully breeding is to examine possible breeding strategies employed by individual males.  Movement patterns, body condition as measured by body fat content, testosterone levels and stress levels are possible factors explaining which males are successful breeders. 
 This study is being conducted on a portion of the King Ranch.  Each autumn, 16-21 males are captured via helicopter net-gunning and fitted with GPS radio-collars which will collect locations every 15-20 minutes until March of the following year.  Age, rump fat measurements, and antler size will be recorded for each male captured.  Furthermore, fecal samples and DNA sample will be obtained from each individual.  About 30-50 fawns will be captured each year and DNA techniques will be used to determine how many, if any, fawns were sired by the collared males. 

Analyzing movement patterns, testosterone and stress levels, and body fat measurements in conjunction with breeding success will help us better understand the breeding system of male white-tailed deer among age classes.  To date, we do not have enough parentage assignments to assess how movements, testosterone and stress levels, and body condition affects breeding success however some movement data has been analyzed.  More information can be found at (insert link).

Population Estimates and Age-Specific Survival of Deer in South Texas
John S. Lewis, David G. Hewitt, John Boulanger, Mickey W. Hellickson, and Fred C. Bryant

Accurately estimating the size of white-tailed deer populations is important to wildlife managers because they help guide management objectives and harvest strategies. Helicopter surveys typically used in South Texas tend to underestimate the number of individuals in a population. We wanted to compare helicopter survey data to estimates of population size using mark-recapture data from 5 ranches participating in the South Texas Buck Capture Project. Additionally, we will examine age-specific survival of deer on these ranches.

Traditional survival analysis performed using both radio-collared individuals or marked individuals that are resighted during helicopter surveys limit the ability of the researcher to determine age-specific survival because of small sample sizes stemming from the expense of radio collars and helicopter flights. We predict deer survival will be positively correlated with deer age and condition. However, harvest strategies such as culling of smaller antlered deer within an age class may create an interaction between antler size and age such that survival for larger-antlered bucks is greater than smaller-antlered individuals within each age class.

In the future, white-tailed deer survival and population estimates will be examined with rainfall data to determine the predictive power of precipitation on fluctuations in population size and survival. We will also investigate the interaction between deer age, antler size, and survival under harvest regimes commonly used in South Texas.

Aging Bias and New Criteria for Aging South Texas White-tailed Deer
John S. Lewis, David G. Hewitt, Mickey W. Hellickson, and Fred C. Bryant

Aging white-tailed deer by tooth replacement and wear (TRW) began with Severinghaus’ paper published in 1949. Since then, many have criticized its utility and determined it to be ineffective for aging older deer. One critic stated that deer could only be placed accurately into 3 age classes: fawn, 1.5, and 2.5+ yr old. By using a large set of known-age mandibles collected from harvested deer marked during the South Texas Buck Capture Project, we wanted to independently evaluate the TRW method by identifying its biases and developing new criteria that allow scientists and managers to more accurately age deer harvested in South Texas.

In general, biologists using the Severinghaus method tend to over-age younger deer and under-age older deer. A test of TRW accuracy for 5.5–8.5+ yr olds ranged from 18 to 33%. We propose 5 separate classes based on TRW patterns from our known-age mandibles: fawn, 1.5, 2.5, 3.5–5.5, and 6.5+. To test this hypothesis, we used an independent set of 75 known-age mandibles that ranged from 2.5–9.5 yrs old. Twenty Texas Parks and Wildlife Department biologists placed these into the 3 older age categories with 72, 73, and 68% accuracy for 2.5, 3.5–5.5, and 6.5+ yr old deer, respectively.

These results are a valuable improvement from the Severinghaus TRW method and previous methods that lump all 2.5+ deer into one category. We believe the division of mature deer into these age categories is biologically useful because our data indicate peak antler growth occurs at 6.5 yrs.

Prior Antler Development as a Predictor of Future Antler Size
John S. Lewis, Mickey W. Hellickson, David G. Hewitt, and Fred C. Bryant

Trophy deer management often involves controlling numbers of both bucks and does. Because the objective of trophy deer management is to produce larger-antlered bucks, many wildlife managers wish to remove the portion of the buck population with the least potential for large antler size. This traditionally includes removing spike-antlered yearling bucks and smaller-antlered older individuals; however, there are little data available to support one culling system over another.

We present trends in antler development comparing gross Boone & Crockett score (GBC) of individuals captured early in life to the same individuals captured at a later date using data from the South Texas Buck Capture Project.
Data from bucks captured from 1998–2007 indicate 3% of spike-antlered yearling bucks scored >150 GBC, while 33% of fork-antlered yearlings scored >150 at 5.5+ years old. Of 3.5 year old deer with ≤ 8 points, only 8% scored >150 GBC, compared to 37% for those with 9 or more points. For 4.5 year old bucks with ≤9 points, 5% scored >150 GBC, whereas 24% of bucks with 10 or more points scored >150.

These criteria might be useful in trophy management of white-tailed deer where the manager can control harvest intensity and selection. Caution is advised for managers of properties where stakeholder interest is in harvesting more deer—not larger deer, or where deer densities or sex ratios do not require removal of bucks.

Repeatability of Antler Characteristics in South Texas
Aaron M. Foley, John S. Lewis, Randy W. DeYoung, Steven D. Lukefahr, Mick W. Hellickson, and David G. Hewitt

A common deer management practice is to cull male deer with spike antlers (i.e. unbranched antlers) and older males with small antlers in hopes that the remaining males will pass on their genes and subsequent offspring will have antlers with desirable characteristics.  Hereditability can only be measured from a population that has a pedigree (i.e. captive situation).  Repeatability is another approach to measure hereditability because repeatability sets the upper limit of hereditability.  A pedigree is not needed to estimate repeatability thus, can be applied to a free-ranging population.
Researchers at CKWRI have records for >4,000 captures of male white-tailed deer during the last decade from 5 ranches in southern Texas, providing opportunity of obtaining repeated measurements of antler characteristics from the same individual.

Measuring repeatability of antler characteristics in a free-ranging population can give us an idea of how repeatable certain antler traits which can provide an estimation of what to expect in respect to next years’ antler size.  For instance, main beam length, number of points, and spread are often used as a criterion for buck harvest.  Establishing repeatability for those antler characteristics may provide insight whether those criterions are useful.  Furthermore, repeatability can also express the extent of environmental influence on antler size.  This is especially important in South Texas, where rainfall varies from year to year.

Habitat Selection and Spatial Partitioning of Male White-tailed Deer in Response to Brush Management
Dean W. Wiemers, Timothy E. Fulbright, Alfonso Ortega-Santos, Allen Rasmussen, David G. Hewitt, Beau D. Hester, and Mickey Hellickson

White-tailed deer preferentially seek areas dominated by herbaceous plants for feeding and use brush for screening and thermal cover.  Deer densities commonly increase in brush-dominated habitats following mechanical clearing to create openings.  This increased use has been attributed in part to greater forb abundance in cleared areas compared to brush-dominated areas.  Our overall objective is to test the hypothesis that habitat selection in male white-tailed deer is driven by thermoregulatory behavior at some upper temperature threshold; whereas, below that threshold habitat selection is driven by forage quality and availability.  A prediction based on this hypothesis is that screening cover is unimportant in habitat selection.  Additional objectives are to determine if 1) male white-tailed deer alter home ranges to forage in recently disturbed patches;  2) intensity of use of disturbed patches declines with time after disturbance; and 3) disturbance alters movement and foraging patterns of deer, and plant community and soil preferences.

About 600 acres within a 1100 acre area will be rootplowed in strips located on the Laureles Division of the King Ranch during summer 2008.  To determine habitat that is selected, 14 male white-tailed deer will be captured and outfitted with global positioning system (GPS) collars.  The GPS collars will be programmed to estimate the deer’s location every 30 minutes for 10 months.  Vegetation biomass, nutritional quality, and screening cover will be estimated in the spring and summer.   Black globe thermometers will be used to estimate operative temperatures in male white-tailed deer within each plant community and in disturbed areas. Results of this research may provide resource managers important habitat characteristics selected and helpful selection of brush management practices that will be beneficial.