Cattle like grass first but will eat brush as a last resort. Deer like weeds first then fall back on browse or brush as a second choice. When I say brush, I mean woody plants like yaupon or trees like hackberry, elm and live oak, or vines like green briar, dewberries or even poison ivy.
Let’s concentrate on deer. Deer ALWAYS prefer native plants over anything you can plant or pour out of a sack. On good range with plenty of choice native forbs, acorns and browse, you can see it happen all the time. Deer will not eat corn. They are not hitting oat and wheat patches. The deer are not touching protein pellets or cotton seed in free choice feeders. They will walk past or over the above to pick up water oak, live oak and especially white oak acorns. With timely rains, forbs and clover will be popping out fresh and green and the deer will be concentrating on that. Hunting becomes poor when nature is at its best.
What happens when there are too many animals? Heavily consumed choice plants will eventually disappear. A leaf on western rag weed is bitten off the second it shows itself. When the small plant tries putting out another leaf that leaf is cut off as well. Eventually the plant dies. A dead plant has no chance of producing seed for the next generation. Over a few years what remains are only plants that a deer does not eat or plants that are very poor quality. The habitat is degraded.
Wildlife biologist and range scientists often call this, “Too many mouths.” Overgrazed cattle ranges will end up with only poor quality grasses and overgrazed deer ranges will end up with only poor quality woody plants. Sad but this happens fairly often. Probably the main reason is greed. A rancher sees 100 cows and wishes he had 150. A hunt manager estimates 200 deer on his ranch and wishes he had 400.
I keep straying. Let’s get back to deer. Keep in mind forbs and acorns are seasonal. Forbs are usually best during late winter and early spring. Acorns hit the ground in the fall and that may not be every year. The cushion or insurance policy all deer fall back on is browse. When the browse is degraded then you have clearly gone too far. It may be too late. Body size will be smaller, fawn crops smaller, antlers smaller, deer will get sick easier. The herd will be stressed.
One of the easiest indicators of too many mouths on a range is a browse line on the trees. This can be seen easiest in the Texas Hill Country where live oak is the dominate tree species. There will be a clear line across the landscape where all or nearly all brush leaves have been removed by browsing deer (it could be goats as well). That line shows you how high a deer can reach while feeding.
When anyone sees this it should be a loud alarm clock ringing in the managers head that he has looming problems. These photos are excellent examples of a ranch that has had its habitat degraded. The only cure is to remove more of the mouths (deer). Remember that the animal that competes for food the most with a deer is another deer.