DEER MANAGEMENT. Where Did They Come From? THE AMAZING REPRODUCTIVE CAPABILITY OF WHITE-TAILED DEER. 70 September 2010

Transcription

1 DEER MANAGEMENT Where Did They Come From? THE AMAZING REPRODUCTIVE CAPABILITY OF WHITE-TAILED DEER. 70 September

2 By Walt Hampton When I was a deer-crazy 10-year-old, I dreamed of rifles, red plaid and deer in the big woods. That year, 1964, Virginia boasted a deer kill of 31,179, 382 of which were taken in my home county of Grayson. In 2009, 4,938 deer were killed in Grayson County, and the Virginia total was 256,512. In fact, during the past 10 years, Virginia hunters have checked in more than 2.27 million legally killed whitetails. Other Southeastern states have experienced similar deer explosions. When I began working for the Virginia Game Department in 1978, a wise deer biologist said, There are almost always more deer out there than you think. As I worked from 1978 to 2004 first for the VGD and later for the U.S. Department of Defense with deer herds across the Southeast, I realized the true meaning of what that meant: Given the proper habitat and management elements, deer are capable of remarkable reproductive success. As hunters looking for recreation, meat and trophies, we take for granted that every pull of the trigger is making a management decision for deer, deciding what our residual population will be and how our actions affect deer biology. When mandatory deer-check stations in Virginia were established in 1947, and 4,019 deer were registered that season, no one would have believed that deer would one day reach current levels certainly not the level of nuisance and damage or the astronomical amount of money the deer hunting industry would generate. By 1930, the national population of white-tailed deer was estimated at 300,000 animals, victims of yearround market hunting and destruction of habitat. Today the population is about 30 million. Where did all these deer come from? BILL MARCHEL September

3 The Learning Curve We can review habitat changes through the years and get a good idea of how they facilitated the increase of deer populations. Also, we know how the birth of modern game management in the 1940s set many animals and birds on the road to recovery. However, the whitetail is still the same animal that roamed the forests when John Smith and Pocahontas dined on Virginia venison 400 years ago. The inherent biological reproductive capacity of the whitetail was in those animals, waiting for the right physical habitat circumstances to present themselves. Efforts to quantify the reproductive capacity of whitetails began in the first third of the 20th century. The most notable was the work done at the Edwin S. George Reserve in Michigan, where in 1928, six deer were introduced into a deer-free 2-square-mile fenced area. Six years later, the first census of the area revealed 160 whitetails. Dale McCullough s book The George Reserve Deer Herd: Population Ecology of a K- Selected Species examined that study and others, and attempted to bring deer reproductive capacity into focus. The book is still available from Blackburn Press georresdeerh.html and I strongly recommend it to anyone interested in whitetails. As hunters and managers we re concerned with our deer herds, especially where the animals have free access to properties where less or more intensive harvest and habitat management might occur. We worry about sustainable numbers of deer on our properties, their sex ratio and age, and what our neighbors are doing that might affect the residual population. State wildlife agencies have given the hunter/ landowner/manager tools, through lengthened seasons and increased bag limits, to make profound changes in deer density and population structures within the constraints of an overall population management goal. How the deer population reacts to practices is manifested in their reproduction. Basic Biology Generally, adult does average two fawns per birth, provided that sufficient quality and quantity of forage is available for the pregnant doe. Statistically, those fawns will typically be one male and one female. In good habitat, about one-third of female fawns will be reproductively active and capable of sustaining a pregnancy at 6 months old. The first pregnancy for a whitetail doe usually results in only one fawn, and the mortality rate of fawns is highest for first-year mothers, which have not perfected their maternal strategies. Conversely, adult does are excellent mothers, and the social behavior of forming maternal groups consisting of a mature doe and her female offspring of the previous two years is a considerable aid in facilitating fawn survival. As you can see from that description, it doesn t take long for the whitetail s reproductive potential to put a lot of hoofs on the ground, especially if food is abundant. In fact, an aggressive female-deer harvest strategy that keeps the population level less than the habitat carrying capacity can actually increase reproductive success by making more food available to individual female deer. I witnessed that phenomenon at Camp Peary, Va., where after several years of aggressive quality deer management reduction of the male harvest and increased female harvest the reproductive rate increased from an average of less than one fetus per doe to more than two fetuses per doe, based on examination of reproductive tracts of harvested does. The calculations for constructing a life table for whitetails are complicated by age and sex-specific mortality, relating to natural predation, disease, hunting and accidents. In the old anti-doe hunting days of population establishment, it was common to hear the old saw that killing a doe was, projected through nine years of her life, killing 18 deer. In reality, because of that deer s reproductive potential, killing one doe could mean the removal of several times that many deer during the same period, if you considered the reproductive potential of her offspring and their offspring during that time. Remember the original example from the George Reserve, from six deer to 160 in six years? Would the ratio be the same if the initial introduction had been 10 times that many deer, say from 60 to 1,600? Theoretically, given abundant food, the answer is a qualified yes. 72 September

4 September

5 How Many Deer Can We Have? Habitat quality and composition determine how many deer can live on a sustainable basis on an acreage. In simplest terms, carrying capacity is defined as the pounds of deer flesh an acreage can sustain and still replace the forage that s eaten each year. Those pounds of deer flesh can be manifested as lots of little deer or fewer, larger deer, but after the limit is reached, habitat starts to degrade. After deer exceed their carrying capacity, there might be a lag time before they begin to show physical evidence of the lower quality and quantity of food. Deer can bounce back quickly from degraded forage quality and quantity if proper corrective steps are taken. Habitat, however, might take many years to recover or can require drastic changes in vegetation to return the quality to original levels. Carrying capacity is independent of the sex ratio of the deer present. Although nutritional requirements for nursing does are higher than for those that aren t pregnant or nursing, deer typically consume 10 to 15 pounds of forage per deer per day. Deer density is usually measured in deer per square mile or deer per acre. If the 2009 kill in Grayson County, Va. 4,938 deer was 25 percent of the total deer population in the county (435 square miles), then the estimated pre-season deer population in the county was 19,752 deer, or about 45 deer per square mile, or 14 acres per deer. That includes acreage in roads, towns, rivers and streams, so the density on actual deer habitat would be somewhat higher. The density is not evenly distributed throughout the county. Some areas are loaded with deer, but others such as densely timbered national forest land are thinly populated. Walt Hampton One Step Forward... What does that mean for modern deer populations and hunters? Considering that deer are more intensely managed now than at any other time, it seems we have done our job too well. In widespread areas, deer have become a nuisance and potential danger to humans, via vehicle/deer interactions, and other animals and plants, through agricultural damage and habitat destruction. Urbanization has created no-hunting zones through wide areas, which have become deer factories. In fact, whitetails can be their own worst enemies where high deer densities facilitate the rapid spread of diseases such as CWD, blue tongue and hemorrhagic fever. As we find new and better ways to enhance deer habitat, creating more and better forage, we increase the potential population level an area can sustain. And as we keep the population less than that habitat carrying capacity through selective harvest, individual deer health improves, and reproductive rates increase. The simple version is, the more you shoot, the more you ll have to shoot. Controlling doe numbers must become an every-year thing. We can t just knock them back and think we ve accomplished population control. At some point in our harvest strategy, we reach a threshold where we must increase doe harvest as a percentage of the total kill to keep the overall population less than a certain level. In the early 1960s, when Virginia s deer population was beginning to expand, a female harvest of 40 percent of the total kill caused the population to crash. Since 2000, doe harvest as a percentage of the total kill has exceeded 40 percent every year, and the kill has continued to increase. In 2010, the percentage of does in the total kill was more than 48 percent. That, coupled with the worst winter in 25 years, will obviously affect the overall deer population. However, the reduction in breeding deer only means that those remaining will have more food, and healthier deer have more fawns. LON LAUBER/WINDIGO Point of No Return? States across whitetail country are finding it more difficult to meet doekill quotas. Most have removed daily bag limits on deer, letting a hunter fill all his tags in one day. In some years, weather, season length and limited recreation time seem to keep hunters out of the woods, and hunters are the mechanism states use to manage deer populations. As we intensely manage whitetail habitat and target deer to improve their quality, we influence their capacity for reproduction. When will we have to say, Enough is enough? Walt Hampton is D&DH s Southeast field editor. 74 September