Kerr WMA: Management Program
Phone: (830) 238-4483
2625 FM 1340
Hunt, TX 78024
Dates Open: Open year round, except closed for Special Permit hunts. The office is open 8am - 5pm, Monday - Friday.
When the Kerr WMA was purchased in 1950, the predominant overstory vegetation was mature Ashe juniper, commonly referred to as cedar. These dense mature stands prevented sunlight from reaching the lower growth stands of vegetation, namely grasses and forbs, and suppressed the growth of these plants. The deer herd at that time consisted of many small deer. A few golden-cheeked warblers may have existed on the Area, and presence of black-capped vireos was highly unlikely.
Historically, this Area was a mid-to-tall grassland savannah with brush and oaks confined to steep canyons and riparian zones. Large numbers of buffalo frequented the area along with pronghorn antelope, black bear, wolves, white-tailed deer, and wild turkeys. Fire and bison played integral roles in maintaining the grassland and prevented brush species from becoming established. That was a time when deer were few, but overall wildlife diversity was rich.
Today, the Kerr WMA is supporting the healthiest plant and animal communities in the Hill Country. Calf weights, white-tailed deer weights (all age classes), fawn survival, antler development, and occurrences of endangered species (golden-cheeked warblers, black-capped vireos, and Tobusch fishhook cactus) have increased under a holistic management program that has evolved over the past 50 years. This program involves brush control, rotational grazing, prescribed burning, deer harvest (whitetails and exotics), and cowbird trapping.
After an integral study, large acreages of mature Ashe juniper were removed from 1964 through 1966 by hand cutting for posts and by chaining. Some stands were left in rough draws, adobe hills, and other sites with a low potential for production to act as cover for wildlife, and a 530-acre parcel was left to act as a relic site and serve as nesting habitat for the golden-cheeked warbler. During this time the Endangered Species Act was not yet in effect nor was the golden-cheeked warbler endangered.
Kerr WMA biologists view livestock as a tool to manipulate and manage for improvement in wildlife habitat and plant diversity. The main role of grazing is to reduce the grass quantity, allowing sunlight to reach the lower growing forb species, which are important white-tailed deer foods. Movement and grazing of livestock in individual pastures is based on growing conditions and season, vegetation conditions of the pasture, soil site, and livestock performance. In grazing management it is very important to remove old decadent grass material, which can shade out new potential growth and prevent new seedlings from becoming established.
By 1979, it was becoming evident to Kerr WMA biologists that neither money nor manpower were going to be able to control the reinfestation of regrowth cedar. So they began experimenting with prescribed fires. Research on these early burns showed that cedars with a less than one inch basal diameter could be easily killed without much harm to the vegetative overstory of canopy trees.
Cattle are grazed immediately in burned pastures for a short period to utilize unburned patches of grass and prickly pear cactus. In one study, cattle following the prescribed fire had consumed 65% of the prickly pear population in the burned area. After a short graze period following the burn, the pasture is rested about 60 days and then grazed again.
Each year about 20% of the Area (800-1,000 acres) are set aside for late winter burns. The burn program has increased the production of grass, browse, and perennial forbs. Biologists have found that preferred deer browse such as redbud and flame leaf sumac increase with fire. White-tailed deer, which are not normally grass eaters, will also consume large quantities of grass in burned areas because it is in a young, tender, and very nutritious state.
Many burned areas have had spots where brush piles were burned and bare soil and ashes existed. Attractants such as salt, range cubes, and blocks have been placed on these bare sites, along with a few native plant seeds. Cattle concentrated on these sites and in a few years they are revegetated and the bare soil no longer exists. The same has been done with bare soil gullies and draws, with the idea being to establish vegetative cover and prevent soil erosion.
In summary, prescribed burning has improved the white-tailed deer habitat by reducing regrowth cedar, improved plants by promoting regeneration of certain browse species, and increased the palatability of more forage species for deer. Over the years, the burn program has helped increase plant quantity and quality and has added diversity to the habitat. Cattle readily use prescribed-burn areas and pastures are put back into the grazing system immediately following burns. This program has also been instrumental in providing nesting habitat for the black-capped vireo. Hill Country rangelands have developed and evolved with fire and grazing animals.
Harvest of surplus deer started in 1954 with a controlled buck-only hunt. Biologists soon realized the need to harvest deer of both sexes to reduce populations to levels at or slightly below carrying capacity. Either sex hunts have been conducted since 1958. The yearly number of hunters chosen to harvest surplus deer is based on the number of deer desired to be removed. Earlier studies conducted on the Kerr have shown that a deer density of one deer per 10 acres could be maintained without a major die-off. The removal of mature stands of Ashe juniper from 1964 through 1966 brought about improved habitat for deer and increased deer numbers.
Deer herd increases soon became a problem. Low fawn crops, major die-offs, small body weights, and inferior antlers were recorded prior to 1968 when deer populations were high and deer food supplies deteriorated on the Kerr. Unsuccessful attempts were made to reduce the deer population to approximately 550 deer on 5,500 acres. Large numbers of deer were removed from the area and short-term range improvement was observed following their removal. However, with ingress of deer from neighboring ranches, actual control of the deer herd was not realized.
In summer 1968, a 7 ½ foot deer-proof fence was constructed around 5,500 acres to stop the ingress from neighboring ranches. Heavy hunting pressure was applied for four years following the construction of the fence and, in 1972, the deer population was brought below the desired carrying capacity.
The endangered black-capped vireo and golden-cheeked warbler utilize the Kerr WMA during their breeding and nesting season, which occurs March through July. Brown-headed cowbirds are also frequently found. The female brown-headed cowbird will lay her eggs in other bird-species' nests and allow the other bird-species to incubate, hatch, and rear her young. Unfortunately, when this occurs in a black-capped vireo nest, young vireos very seldom survive. Studies have shown that up to 75% of the vireos' nests are predated by brown-headed cowbirds. This factor, along with shrinking nesting habitat, has led to low numbers of vireos during the past decade. Brown-headed cowbirds are often attracted to and feed in areas grazed by large herbivores such as cattle, horses, deer, and bison. The cowbird was originally called the "buffalo bird" and traveled with the bison herds before cattle arrived on the scene.
Initially, cattle were not grazed in areas during the vireos' prime nesting time. However, biologists found that cowbirds can be easily trapped and removed which means nesting success of vireos increases dramatically. In 1988 cows were grazed in the area just prior to nesting period, enabling biologists to trap more cowbirds. Nest parasitism dropped significantly. Biologists then developed a "mobile" cowbird trap, which could be moved with the cow herd.
An intensive three-year study has shown that nest parasitism has dropped to 12% in the main vireo nesting colony. Surveys of singing males show claimed territories have grown from 27 in 1986 to 422 in 2002.
Effects of Long-Term Rest
In 1954, a 96-acre deer and livestock grazing exclosure was established on the Kerr WMA. No livestock grazing has occurred in this exclosure for the past 42 years.
Does this long term rest from grazing animals allow maximum plant diversity and quantity which may have existed prior to European man's arrival? Not according to data gathered from the 42-year grazing exclosure. There was a positive response in the abundance and number of grasses and forbs found in the exclosure until the early '60s. The number of grass and forb species encountered on vegetative line transects have decreased from 47 species in 1960 (an all time high), to 14 species in 1989 (an all time low since 1960). These same transects have also shown that the amount of bare ground has increased significantly since 1962. Only one species of forb was encountered on these transects in 1989. This decrease in plant diversity and quantity can be credited to over-rest or a "do nothing" non-management program.
In contrast to the grazing exclosure, the remainder of the Kerr WMA has increased in plant diversity and quantity. The vegetative transects in the grazed and burned pastures have shown that the grass cover has increased dramatically during the last few years, resulting in less bare ground and soil exposure. These transects showed an all time high of documented grass cover in the history of the Kerr. Forbs and browse species have shown these same upward trends. In fact, nine new species of forbs have been found growing and documented on the area in 1990 and 1991, a welcomed addition to the 205 forbs, 79 browse, and 73 grass species that were already documented on the area's plant checklist.