The population of white-tailed deer in Central Texas has rapidly grown over the last century due to a number of factors—including a decline in natural predators such as mountain lions and wolves, suppression of the blow fly screw-worm parasite by cattle ranchers, and a ban for several decades on the hunting of does. Another important reason for the population increase is urbanization. Residential developments provide a variety of edible and accessible plants, with some homeowners even supplementing this food supply with salt blocks, corn, and pellets.
The deer population on the Balcones Canyonlands Preserve exceeds the carrying capacity of the ecosystem, which is the maximum number of deer the ecosystem can support without degradation of habitat. Passing this upper limit leads to increased competition for limited food resources, causing starvation and disease in the deer population. These large populations of starving deer will begin to browse on plants they normally would avoid—a problem known as overbrowsing.
The most common sign of deer overpopulation is the browse line, where all vegetation from about five feet high down to the ground is stripped of leaves. Although the mature oak and juniper trees are often tall enough to escape extensive browsing, overbrowsing still has a devastating effect on golden-cheeked warbler habitat because it removes all seedlings and saplings that could eventually develop into mature trees. Overbrowsing also removes other understory vegetation (shrubs, grasses, and wildflowers) that is essential for preventing soil erosion, protecting water quality, and providing habitat for a large range of animals, including the endangered black-capped vireo.
The most cost effective solution available for deer overpopulation is lethal, humane culling by professionals, which replaces the ecological role of the now-absent top carnivores. Wild mammal contraceptives are being researched for possible future use, but currently are not practical or effective on a large scale and have not been approved for use in Texas. The meat produced by culling is required by state law to be used beneficially and is usually donated to food banks and similar charities. Last year, the City of Austin donated over 6,000 pounds of venison through the Hunters for the Hungry program to the Capital Area Food Bank — a non-profit organization providing food to hungry people across Central Texas.