The Deer Who Share Our Gardens
Those of us who garden in southern and eastern New England realize that deer have become common, even in the more built-up suburbs. Deer/car collisions are definitely on the rise, as we all read in the newspapers. Damage to landscape plantings is a constant complaint now. The population of Whitetail Deer has reached an unprecedented level in recent years. There are more deer in New England now than there were in the primeval forests before the European settlers arrived. There are many more than in the 18th and 19th centuries when most of southern New England was open, cultivated land and the Whitetail was almost extirpated. Our suburban landscape with its expensive plantings of ornamental shrubs, with its surrounding second-growth woods and abandoned farms growing up into forest, are perfect deer territory. Deer are not grazing animals who eat soft, grassy plants but ruminant browsers who feed on woody materials. While they are big animals, they cannot browse on anything much above six feet, so they cannot prosper in deep mature woods with a dense canopy and no understory. They need low, shrubby growth or young trees. They need your rhododendrons and kalmias, your prize stewartias, workhorse yews, fruitful blueberries, and rare Japanese maples!
The Whitetail Deer, Odocoileus virginianus, is a member of the family Cervidae, hoofed, ruminant, antlered mammals including elk, moose, and caribou. They are big animals, much larger than any of the other animals found in our yards, except for the occasional adolescent bull moose that wanders into eastern Massachusetts. A full-grown male Whitetail deer can weigh over 300 pounds, the females up to 250. They are a soft, reddish brown in the summer and a muted grey-brown in the winter, with white bellies, throats, nose bands, eye rings and the underside of the tail. The tail is flashed up in flight, a bright white `flag', to alert other deer to danger and to help fawns follow their mothers. (This `hightailing' is why walkers in the fall woods should not use white tissues or wear white gloves or scarves.) Deer give a whistling snort when disturbed and often stamp their feet as a warning of danger. They can run 35 mph with a beautiful springy stride, but they prefer to bolt for nearby cover where they instantly vanish from sight. They are strong swimmers and lakes and rivers are no barrier for them. They are beautifully camouflaged and wary to the point of secretiveness; we live in the midst of them and only rarely see them when we stumble across one of their habitual routes or catch them in the car headlights.
Deer gather in herds only in the late Fall and Winter when the animals form small groups and share winter `yards', protected bedding areas usually among dense evergreens. The bucks are solitary the rest of the year; the females stay with their current fawns (born in spring) and sometimes their previous year's offspring. Mating takes place in the fall, with a 6 to 7 month gestation. First year does produce one fawn, but thereafter they will throw twins or triplets. The spotted fawns are able to run moments after birth and surprisingly odorless for their first few weeks; they hide motionless and all but invisible from predators unable to smell them.
Males grow racks of antlers up to 33 inches; contrary to oft-repeated statements, the size of the rack is determined by the quality of the buck's food supply and his health, not his age, which is calculated accurately only by tooth wear. Lengthening daylight stimulates hormones which trigger antler growth. As they grow, they are rubbery tissue full of blood vessels which feed the growing soft bone; they are covered with fine hair called `velvet'. In early fall the blood stops flowing and the calcareous, bony matter dries into hard horn; the male rubs off the now peeling skin on small shrubs and saplings to mark territory. One can sometimes find these small trees with scratched and shredded bark near ground level. Bucks are now in rut and can be dangerous, all caution abandoned in a high testosterone search for does in heat and in defense of their mating territory. A buck will mate with any ready female he can keep from other males; there is no permanent pairing, just an enthusiastic coupling and then separation. Antlers are shed after the mating season, usually both racks within a few days of each other. Humans rarely find discarded antlers because other animals immediately avail themselves of the calcium in them; they are more porous than regular bone and easily gnawed.
A deer skull reveals a great deal about their eating habits. On the bottom jaw they have large, sharp front cutting teeth and then a surprising area of blank jaw. At the back are massive molars with sharp points on the grinding surface, very different than the broad, flat grinding molars of grazing animals like cattle and sheep. The upper jaw has a horny, tough gum in the front with no teeth at all; the rest of it matches the lower jaw. Deer cut and tear off woody shoots, using their sharp incisors against that thickened upper gum (think of anvil style pruners) and jerking their heads to tear off what they have not severed. They chew the browse only enough to swallow the twigs, not into their true stomachs but into a separate rumen where the woody material is stored. Most browsing takes place around dawn and sunset as the animals move quickly and warily around. The rest of the time the animals rest and chew their cud with those sharp back molars; cud are small packets of undigested food regurgitated from the rumen into the mouth. When the woody food is fully crushed and moistened, the food is swallowed into the true stomach, a complex organ with many chambers where microorganisms break down the cellulose, a remarkable accomplishment. (Remember that most animals that `eat' woody plants actually digest only the nutrient-rich cambium layer and bark, not the pith underneath.) Diet varies somewhat with the season; deer will eat fungi, acorns, grass and soft plants along with twigs and leaves when they are available in warm seasons and the buds and twigs of woody shrubs and trees when there is nothing else. Their scat varies with diet; they produce their familiar hard, dark oblong pellets when their diet is woody, and cylindrical, even massed scat when they are eating soft, fresh vegetation.
Deer stomachs are also equipped with a complex variety of enzymes which allow the deer to break down moderate quantities of toxins in the plants they eat. As many homeowners have ruefully learned, rhododendrons, laurels and yew bushes, which are all poisonous, are favorite browse for deer. The deer do not eat great quantities of any one kind of plant in a single feeding and thereby avoid poisoning; their digestive systems can handle several different plant toxins at once, but not a great quantity of any one toxin. This is a remarkable evolutionary adaptation to a less-than-abundant food source in mature forest.
We now have many more deer than at any period in New England history. We have eliminated their predators and maximized their brushy food supply so that their population is growing rapidly. Cars and dog packs are now their greatest threats, but they can hardly be considered as methods of population control. If society agrees that the population of Whitetails must be reduced, then we probably will have to rely more on hunting to keep the numbers down, although we can't safely allow hunting in populous areas, no matter how many deer our suburbs hide. Moreover, the conventional hunting style of taking antlered bucks actually has little overall effect on the population, since any male will mate with any and every available female. Even a first year buck, only six months old, will mate if no older male drives him off. A substantial reduction of males in the population will have almost no effect on the number of fawns in the Spring. We have created an increasing problem for which there seems to be no easy solution. We should expect more deer/car collisions and more cries of outrage and frustration from gardeners contemplating the ruin of favorite plants. The Whitetails may be unseen in our yards, but they will not be unnoticed!