Last month we discussed the 2012 hemorrhagic disease (HD) outbreak [July; Page 24]. This month we will explain how HD and other factors affect deer populations in Missouri. A deer population increases or decreases based on the difference in birth (fecundity) and death (mortality) rates, which are often influenced by regulations, forage availability (i.e., acorns), predator abundance, and disease outbreaks.
Antler Point Restriction
The primary goal of the antler point restriction (APR) was to lower deer densities by increasing doe harvest, not to increase buck age structure. The two might seem unrelated, but often hunters resort to harvesting a doe when they have to pass on young bucks that do not meet the APR. The increased doe harvest yields lower deer densities over time, but also increases buck age structure, as younger bucks are often protected from harvest by the APR. Since the APR has been shown to decrease deer density, at this time it is not biologically or socially acceptable to expand the APR statewide, as deer populations in many southern counties are currently at or below desirable levels and unable to sustain increased doe harvest.
After the APR is implemented, doe and button-buck harvests tend to increase and antlered-buck harvest decreases as hunters fill permits with antlerless deer when unable to harvest a legal buck. As a result, buck survival increases, allowing them to mature into older age classes. As more bucks are recruited into older age classes, buck harvest again increases after the initial implementation of the APR. Additionally, over time, doe harvest is predicted to decrease as deer populations are reduced and does compose a smaller proportion of the population.
Antlerless Permits and Season
The intended purpose of antlerless permits and season is to allow hunters the flexibility to manage deer populations and address deer issues, while providing additional hunting opportunity. However, there is a misperception that when “any number” of antlerless permits are available the population can sustain high doe harvest. A harvest of approximately 20–25 percent of the adult doe population will keep the population stable, any more and the population will decrease, and any less will lead to population increases (see A Deer Harvest Scenario).
Acorn production can have a substantial effect on deer populations in forest-dominated areas, like southern Missouri. In heavily forested (more than 50 percent) landscapes, acorns compose the majority of a deer’s fall and winter diet. However, in poor acorn crop years, like 2012, deer have to search farther and more frequently for food, often leading them to concentrated food sources such as agriculture, early successional areas, and open areas with high forb abundance. Deer sightings increase and their vulnerability to harvest increases substantially, causing higher deer harvests in forest-dominated areas during acorn “bust” years. However, the opposite occurs in years of good acorn abundance by causing deer to become more evenly distributed with shorter daily movements, thus decreasing sightings and harvest. Areas not dominated by hardwoods, like northern Missouri, experience less acorn production effects, which results in a consistent harvest vulnerability more reflective of actual population trends.
Hemorrhagic disease (HD) can cause local deer populations to decline, but often have minimal long-term, large-scale effects. The causes of HD outbreaks are localized and not completely understood. For example, during 2012, Osage County had the highest reports of deer mortality, but the majority of the reports were limited one area, with the remainder of the county minimally affected.
Hemorrhagic disease outbreaks in Missouri are often sporadic (rarely occurring in consecutive years) and severe, while in southeastern states they are frequent (every 2–3 years) and mild. Missouri experienced significant HD outbreaks previously in 1988, 1998, and 2007; however, the 2012 outbreak appears to be the most widespread and intense on record in Missouri. Unfortunately, there is no way to quickly determine the HD–related mortality within affected areas. Also, the reports that we received are only a small proportion of the mortality that actually occurred as many go unreported.
Ultimately, the population response to an HD outbreak is related to the amount of mortality and growth rate of the population. As mentioned previously, growth of the population is related to births and deaths. If a population has more does than bucks, it will have a higher growth rate than a population of similar total size, but with equal numbers of bucks and does. Additionally, harvest rate greatly influences how a population responds to an HD outbreak. For example, an area where less than 20–25 percent of the adult does are being harvested consistently will recover quicker than a population with doe harvest greater than 20–25 percent. As a result, deer populations vary across the state and will respond in different ways to the recent HD outbreak. Ultimately, the populations with low growth rates coupled with high harvest rates are of greatest concern.
During the past few years there has been increasing concern regarding the effect of predators, specifically coyotes, on deer populations. While there have been several coyote predation studies in the southeastern U.S., those results are not applicable in Missouri because coyote populations have historically been present in Missouri, but are relatively new to the southeast. Additionally, recent investigations suggest that southeastern coyotes differ in behavior and appearance from their Midwestern counterparts. While admittedly outdated, research in Missouri has shown that deer make up a small portion of a coyote’s diet and much of that appears to be the result of scavenging on deer and not killing. Regardless, significant increases or decreases in carnivore populations can influence deer mortality rates, especially of fawns.
Missouri Deer Management Mission Statement
The mission of the deer program is to use science-based wildlife management to maintain biologically and socially balanced deer populations that provide quality recreational opportunities and minimize human-deer conflicts.
Statewide population trends are misleading when discussing localized deer population dynamics. Therefore, localized or regional information is more indicative of actual deer population trends observed by hunters and the public. However, there can be considerable variation within a region or even a county. Therefore, regional information should be considered as a starting point when evaluating local deer populations.
There is great variation among deer populations within the Central Region. Parts of Audrain, Boone, Callaway, Cooper, Howard, and Saline counties have experienced population declines in the past decade as a result of multiple hemorrhagic disease outbreaks (2007, 2010, and 2012) and high doe harvest. The poor acorn crop boosted the 2012 deer harvest in Cole, Camden, Gasconade, Maries, Miller, Morgan, and Osage counties, increasing by 12 percent from 2011 and 6 percent greater than the 10-year average. It is expected that localized areas will have smaller deer populations over the next several years. As a result, a reduction in doe harvest permits in some Central Region counties is necessary to overcome population declines.
Kansas City Region
Harvest in the Kansas City Region in 2012 was down 6 percent from 2011, which follows a general trend of reduced harvest across the rural areas of the Kansas City Region over the past decade. Counties with the greatest decrease in the 2012 harvest compared to the 10-year average were Platte, Bates, and Pettis, while Benton County increased. A large portion of the region was hit hard by hemorrhagic disease in 2012, with Benton and Henry counties having the most reported cases within the region. In rural areas affected by hemorrhagic disease, it may be necessary to reduce doe harvest to allow deer populations to recover.
Deer populations in the Northeast Region have been slowly decreasing over the last several years; however, some areas still have high deer populations. Several areas within the Northeast Region experienced significant hemorrhagic disease mortality, which likely contributed to the 6-percent decrease in deer harvest from 2011. In general, deer populations in many parts of the Northeast Region have been stable to slightly increasing, including Adair, Lewis, Putnam, Sullivan, Clark, and Schuyler counties. Some counties have experienced declines with the most dramatic being in Monroe, Randolph, and Shelby. However, the 2012 hemorrhagic disease outbreak will result in some localized reductions in deer populations. Localized decreases in doe harvest, without regulation changes, should be sufficient to allow recovery of populations reduced by hemorrhagic disease mortality.
There has been a steady reduction in the deer population and harvest over the past decade in the Northwest Region with harvest in 2012 decreasing by 10 percent from the 10-year average. Declining harvest is a reflection of lower deer populations across many counties, including Atchison, Caldwell, Carroll, Clinton, Daviess, Nodaway, and Ray. Large concentrations of deer are far less common today than in the early 2000s in many of these areas. In areas that were heavily affected by hemorrhagic disease in 2012, a reduction in doe harvest is likely warranted to aid population recovery. However, a few counties, including Worth and Mercer, continue to have strong deer populations. Additionally, changes in land use within the region are reducing the amount of available habitat, which may be contributing to localized reductions in deer density.
Deer populations in the Ozark Region have been slowly increasing over the past decade as a result of continued conservative regulations on antlerless harvest. A slowly increasing population and poor acorn abundance is reflected by a 22-percent increase in deer harvest from 2011 to 2012. Ozark counties with the greatest deer harvest increase compared to the 10-year average harvest were Pulaski, Shannon, Carter, Howell, and Ripley. Both 2010 and 2011 had relatively good acorn crops, which, as previously mentioned, made them less vulnerable to harvest, allowing populations to increase. The past years of good acorn production also provided much-needed nutrition, potentially resulting in greater fawn production, which helps boost populations. Increased deer populations across the Ozarks are well accepted as deer populations remain below biological and social carrying capacity.
Deer populations in the Southeast Region have been slowly increasing over the past decade, which is reflected in harvest trends. Slowly increasing populations and a poor acorn crop resulted in a 22-percent increase in deer harvest from 2011 to 2012. The previous two years experienced good acorn production, made deer less vulnerable to harvest, and increased fawn production. Populations are expected to continue slowly increasing, as regulations remain restrictive. Increased deer populations across the Southeast Region are well accepted because, in most locations, populations remain below desirable levels. Additionally, the Southeast Region appears to be the only Missouri region to escape significant deer mortality due to hemorrhagic disease in 2012.
St. Louis Region
Outside of the urban areas, the St. Louis Region deer populations have been stable or slowly increasing over the past several years. Deer harvest in the St. Louis Region in 2012 increased 18 percent from 2011. The increased harvest can be partially attributed to the poor acorn crop in the southern parts of the region, especially in Washington, Franklin, and Jefferson counties. The St. Louis Region did experience moderate hemorrhagic disease mortality in 2012, but was not as severely affected in comparison to other regions across the state.
Deer populations in most of the Southwest Region have been slowly increasing since a reduction in the availability of antlerless permits was instituted in 2008. In 2012, poor acorn production resulted in more deer sightings by hunters, resulting in an increased harvest. Thus, harvest in the Southwest Region was up 12 percent from 2011, but may be more reflective of a poor acorn production rather than the slowly increasing population. The greatest harvest increase during 2012 compared to the 10-year average occurred in Stone, Dallas, Greene, and Laclede counties. Like many other parts of the state, the Southwest Region was hit hard by hemorrhagic disease in 2012. With the increased harvest and hemorrhagic mortality, we expect some areas to have reduced deer populations over the next few years. In local areas where population declines are apparent, landowners and hunters should consider harvesting fewer does in 2013.
A Deer Harvest Scenario
The following is an example of how to determine the appropriate number of does to harvest to increase, maintain, or decrease a deer population that is estimated at approximately 31 deer per square mile.31 deer per square mile 35 percent of the population are fawns
- Approximately 11 fawns per square mile65 percent of the population are adults
- Approximately 20 adults per square mile1: 2 Adult sex ratio (buck : doe):
- Approximately 7 bucks per square mile
- Approximately 13 does per square mile
- Increase population:10–15 percent, or two or fewer adult does per square mile
- Stabilize population: 20–25 percent, or three adult does per square mile
- Decrease population:30–35 percent, or four or more adult does per square mile