White-tailed deer

• 1. Introduction

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  When a white-tailed deer senses danger, it lifts its tail and flashes the white underside. The animal, known scientifically as Odocoileus virginianus, goes by the names whitetail and Virginia deer. It is a medium-sized deer native to both North and South America. No other hoofed plant-eater on the American mainland is spread across a wider area. Its habitats run from arid grasslands to the Amazon and Orinoco basins, and from the Llanos to the high terrain of the Andes. How does a single species fit so many landscapes? What do forests, farms, and roads look like once its numbers climb? And what does a deer carry with it into the places people live? The answers start with the map.

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• 2. Range and Subspecies

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  Texas holds an estimated 5.3 million white-tailed deer, more than any other U.S. state, Canadian province, or Latin American country. That tally covers wild animals and farmed herds raised for large antlers and for breeding. High numbers also live on the Edwards Plateau of Central Texas and in states such as Illinois, Iowa, Minnesota, Ohio, Pennsylvania, and Wisconsin. In parts of the east and south, the animal is common enough to be considered a nuisance.

  West of the Rocky Mountains the picture changes. The black-tailed deer fills the whitetail's niche in the Pacific Northwest, and the mule deer holds much of the country to the west. The westernmost whitetail population, the Columbian white-tailed deer, once ranged through mixed forests along the Willamette and Cowlitz River valleys of western Oregon and southwestern Washington. Its numbers are now much reduced, and the IUCN classifies it as near-threatened.

  Human land use has pushed the range in other directions. Farmland carved from country beside the Canadian Rockies, along with partial clear-cutting of conifers that left deciduous growth behind, carried the species as far northwest as the Yukon. Around the Great Lakes, farming also drove whitetails north and west, while local caribou, elk, and moose declined.

  Taxonomists have long argued over how many kinds of whitetail exist. Over the last century, some scientists described 30 to 40 subspecies, mostly from differences in body form. Genetic studies point to fewer. One current list names 38, of which 17 occur in North America. The Florida Key deer and the Columbian white-tailed deer are both listed as endangered under the U.S. Endangered Species Act.

  Several subspecies are named for tiny places. South Carolina has a Hunting Island deer, a Bulls Island deer, and a Hilton Head Island deer. Georgia has the Blackbeard Island deer, and Panama has the Isla Coiba deer. Margarita Island and Curaçao each have their own too.

  Farther south, subspecies stretch from Guatemala to Peru. That list is longer and shakier than the North American one. Overhunting and little protection have made these deer hard to study, and some areas no longer hold any deer at all.

  People have also carried whitetails abroad, mostly for sport hunting. They were released in New Zealand, in the Greater Antilles of Cuba, Jamaica, Hispaniola, and Puerto Rico, and in several European countries. In Nova Scotia, they killed off the native caribou through brainworm. On Prince Edward Island, they were eradicated.

  Europe saw whitetails from the second half of the 19th century. In 1884, one of the first European hunts took place at Opočno and Dobříš, in the Brdy Mountains area of what is now the Czech Republic. A Brdy population remains stable today.

  Finland's story began in 1935. Four animals, provided by Finnish Americans from Minnesota, founded a herd that spread through northern Scandinavia and southern Karelia. By 2020 it numbered some 109,000 deer, sometimes displacing native species. In the Andes, whitetails live above 13,000 feet, and they look different there.

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• 3. Coat, Eyes, Antlers

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  At the former Seneca Army Depot in Romulus, New York, stands the largest known concentration of white deer. These animals are entirely white except for the nose and hooves, and they are not albino. Strong conservation efforts have let them thrive inside the depot's boundaries.

  Most whitetails wear a reddish-brown coat in spring and summer, which turns grey-brown through fall and winter. Older deer tend to show longer snouts and grayer coats. Andean deer are larger than other tropical whitetails and have thick, slightly woolly-looking fur. They keep gray coats, apparently because of the cold at altitude, while lowland savanna deer keep reddish brown.

  Size follows Bergmann's rule and Allen's rule, growing larger farther from the equator. North American bucks usually weigh 150 to 300 lbs. Bucks over 400 lb have been recorded in the northernmost reaches, in Minnesota, Ontario, and Manitoba. In 1926, Carl J. Lenander Jr. took a buck near Tofte, Minnesota, that weighed 183 kg after field-dressing and was estimated at 232 kg alive.

  Does in North America usually weigh 40 to 90 kg. Deer from the tropics and the Florida Keys are far smaller, averaging 35 to 50 kg, and an occasional adult female weighs just 25 kg. Across all races, the average summer weight is 68 kg for adult males and 45 kg for adult females. In South America, only the marsh deer is larger.

  The eye of a whitetail has a horizontally slit pupil, which gives it good night vision and color vision by day. Whitetails process images faster than humans do, and they detect motion in dim light better. Their vision is dichromatic, with blue and yellow primaries, whereas humans normally see three primary colors. Oranges and reds therefore look dull to a deer, which is why hunter orange works as a safety color on caps and clothing.

  Males regrow their antlers every year, and growth begins in late spring under velvet, a tissue rich in blood vessels. About one in 10,000 females also grows antlers, usually in connection with freemartinism. Length and branching depend on nutrition, age, and genetics. Protein and calcium matter, and well-fed deer in some areas carry eight-point antlers as yearlings.

  Antlers are still a poor guide to a buck's age, because the local environment shapes them. Bucks without branching antlers are called spikes or spikehorns. Button bucks are different. They are male fawns, about six to nine months old in their first winter, with only skin-covered nobs on their heads.

  Typical antlers are symmetrical, with points growing straight up from the main beam. Atypical antlers are asymmetrical, with points projecting at any angle. The Boone and Crockett and Pope and Young scoring systems measure how much of a rack is asymmetrical, so a slightly uneven buck still scores as typical. A buck's inside spread can run from 3 to 25 in. Bucks shed their antlers once all the females have been bred, between late December and February.

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• 4. Predators and Flight

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  Gray wolves are the leading cause of deer mortality wherever they overlap with whitetails, from northern Minnesota, Wisconsin, and Michigan across most of Canada. Cougars, American alligators, jaguars, and humans rank among the most effective natural predators too. Jaguars hunt whitetails in the American southwest, Mexico, and Central and South America. Aside from humans, these hunters tend to pick off easily caught young or infirm deer, which is believed to improve a population's genetic stock. They can and do take healthy adults of any size.

  Bobcats, Canada lynx, grizzly and American black bears, wolverines, and coyote packs mostly go after fawns. Lynx, coyotes, and wolverines are most likely to take adults when harsh winter weather has weakened them. Scavengers, including New World vultures, raptors, red and gray foxes, and corvids, rely on deer as carrion.

  American crows and common ravens have been recorded pecking around the faces and eyes of fawns, though no success is reported. Golden and bald eagles occasionally capture fawns with their talons. In Illinois, a golden eagle was filmed failing to bring down a large mature deer.

  The methods differ by predator. Cougars and jaguars first knock a deer off balance with their forelegs, and felids then bite the throat to suffocate it. Bobcats and lynx jump astride the deer to deliver the killing bite. Canids and wolverines bite the limbs and flanks until the deer is hobbled and bleeds out. Alligators snatch deer that are drinking or crossing water and drag them under to drown.

  Most of these hunters ambush, though canids may chase a deer to exhaustion. A whitetail's answer is to breathe heavily, a behavior called blowing, which alerts other deer, and then to flee. It can sprint at 40 mi per hour and sustain 30 mi per hour over distance, among the fastest of all deer alongside the Eurasian roe deer. It can jump 9 ft high and 30 ft forward.

  The style of flight depends on the threat. When shot at, a deer runs at high speed with its tail down. When merely frightened, it hops in a zig-zag with its tail straight up. If it feels extremely threatened, it may charge, using antlers or, lacking those, its head.

  In eastern North America, most of the primary predators have been wiped out. A very small number of reintroduced, critically endangered red wolves live around North Carolina, along with a remnant population of Florida panthers, a cougar subspecies. Coyotes, with a rapidly expanding population, are often the only major nonhuman predator in the Eastern U.S., besides an occasional domestic dog.

  In north-central Pennsylvania, black bears were found to be nearly as common fawn predators as coyotes. Bobcats exploit deer mainly when smaller prey is scarce. Around the Great Lakes, the abundant deer have helped the wolf population recover.

  Some people have discussed bringing gray wolves and cougars back to parts of the eastern United States. The model was Yellowstone National Park, where reintroduced wolves checked a previously overpopulated elk herd. Heavy urban development and fear for livestock and human lives led communities and government services to reject the idea.

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• 5. Appetite and Forests

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  A grown whitetail can eat around 2000 lb of vegetable matter in a single year. A population of around 20 per square mile can start to destroy the forest in its foraging area. The menu includes shoots, leaves, prairie forbs, and grasses, cacti in deserts, plus acorns, fruit, and corn. Around farmyards, deer also eat hay and white clover.

  The whitetail is a ruminant with a four-chambered stomach, and each chamber has its own function. Food can be swallowed quickly and digested later in a safe patch of cover. The stomach hosts microbes that shift with the seasons as the diet changes. If the microbes for a particular food, such as hay, are missing, that food will not be digested.

  Through foregut fermentation, the partly digested food, called cud, is regurgitated and chewed again with saliva. Smaller particles absorb better, and saliva supplies liquid for the microbes, recirculates nitrogen and minerals, and buffers the acidity of the rumen. This system lets deer eat mushrooms, even ones toxic to humans, and poison ivy.

  Almost entirely herbivorous, whitetails will still snatch nesting songbirds, field mice, and birds trapped in mist nets when need arises. When they need more calcium or other minerals, they may chew the bones of dead animals, a habit called osteophagy.

  The foods deer prefer are rare in mature forest and are mostly found at edges, where different kinds of vegetation meet. Suburbs are full of edges. They offer safety from some predators, including hunters, along with rich food in home gardens, city parks, and open farmland, so deer thrive there.

  In parts of eastern North America, dense deer herds have sharply reduced plant biomass, including the density and height of forest wildflowers, tree seedlings, and shrubs. Browse-tolerant grasses and sedges and unpalatable ferns have often taken over. Changes to the forest understory have altered the makeup of bird communities in some areas.

  At intermediate densities, the effect can be positive. Deer feeding has been shown to raise the diversity of herbaceous plants in disturbed areas by cutting back dominant competitors. It may also speed the growth of important canopy trees, perhaps through added nutrients in the soil.

  In northeastern hardwood forests, deer change what grows back after clear-cuts and patch cuts. Without deer, annual herbs and woody plants give way to commercially valuable oak and maple, which tolerate shade and keep out cherry and American beech. Deer eating the early plants lets in light, and the stronger nutrient competitors invade. Oaks grow slowly and need several decades to build adequate roots, so cutting the canopy too soon magnifies the deer's influence.

  A study of eastern hemlock forests found that browsing by deer made three exotic plants spread faster than in deer-free areas. Their seedlings rose exponentially with deer density, while the most common native species fell exponentially, because deer preferentially ate the native plants. Canopy disturbance magnified both effects. Some have wondered whether deer could browse hemlock seedlings out of existence, but browsing is not considered the critical factor in blocking hemlock recovery at large scales.

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• 6. Scent, Sound, Rut

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  A newborn fawn calls to its mother with a high-pitched squeal known as a bleat. As the fawn grows, the bleat deepens until it becomes the guttural grunt of a mature deer. A doe makes maternal grunts when searching for her bedded fawns. Bucks grunt at a lower pitch, and that grunt deepens with age.

  Both sexes snort, a sound that often signals imminent threat. Mature bucks also produce a grunt-snort-wheeze pattern unique to each animal, asserting dominance, aggression, and hostility. Tail-flagging, the raising of the tail on detecting a threat, has a disputed purpose. It seems to signal predators more than to warn other deer.

  Whitetails carry many scent glands, and some secretions are strong enough for the human nose to detect. The four major ones are the preorbital, forehead, tarsal, and metatarsal glands. Research suggests that the preorbital secretions, long thought to be rubbed on branches, are not used that way. The forehead glands, between the antlers and eyes, deposit scent on branches that overhang scrapes. The metatarsal glands, on the outside of each hind leg, may release an alarm scent.

  The interdigital glands, between the hooves, give off a yellow waxy substance with an offensive odor. A deer that senses danger may stomp, leaving a heavy dose of that smell as a warning. The tarsal glands sit on the upper inside of each hind leg's hock. Throughout the year, deer rub-urinate: they squat so urine runs down the insides of the legs, over the tarsal glands. Secretions from the preputial and tarsal glands mix with urine and bacteria into a strong odor, and bucks do this more during breeding season.

  A rub is made when a buck strips bark from a small tree with his antlers, marking territory and polishing the antlers. A scrape is bare earth exposed by his front hooves, often in lines called scrape lines. He rub-urinates into scrapes, which usually lie under twigs marked with forehead-gland scent. Bucks do most of the marking, but does visit these sign-posts often. Bucks use them to learn which rivals are around, and does learn that a buck passes regularly.

  The breeding season, called the rut, starts in autumn, normally in late October or early November, triggered mainly by the declining length of daylight. Bucks spar to settle a dominance hierarchy. They try to mate with as many does as possible, and they rarely eat or rest, so they gradually lose condition. The rut is shorter at higher latitudes. When the temperature rises above 40 F, bucks travel much less in search of does, to avoid overheating or dehydrating. Competition matters too, and more males in an area means fiercer rivalry.

  Some does reach sexual maturity at six months, though the average is 18 months. Maturity depends on population density and food supply. Bucks are generally mature at 1.5 years and breed even where older bucks are plentiful.

  Fawns arrive in mid-to-late spring, usually in May or June, in litters of one to three. For the first four weeks, the mother hides them in vegetation and nurses them four to five times a day. This keeps scent levels low and predators away. After about a month, fawns follow her on foraging trips. They lose their spots during the first summer and weigh 20 to 35 kg by the first winter. Weaning usually comes after 8 to 10 weeks, though some mothers let fawns nurse for months. Males leave their mothers after a year, and females leave after two.

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• 7. Collapse and Rebound

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  By about 1930, the U.S. whitetail population was thought to number only about 300,000. Commercial exploitation and unregulated hunting had severely depressed deer across much of their range, after the species was hunted nearly to extinction in the late 1800s and very early 1900s. An outcry from hunters and conservation ecologists made commercial exploitation illegal and brought conservation programs and regulated hunting. By 2005, estimates put the U.S. population at around 30 million.

  North America has lost several million whitetails since 2000. As of 2017, the population was considered healthy and roughly equal to the pre-colonization level. The whitetail's closest cousins fared worse. Blacktail and mule deer populations were cut by more than half after peaking in 1960, and they have never regained their old numbers. Habitat loss to development and changes in logging have more than offset the loss of natural predators.

  Hunting of whitetails is old. In Mesoamerica, people hunted them from very early times. Rites to prepare for a hunt and celebrate a good one are still practiced there. Ancient hunters ask their gods for permission to hunt, and some deer rites take place in caves.

  Today the whitetail is probably the most hunted native big game species in the Americas. The top five states for hunter concentration are Pennsylvania, Rhode Island, New York, Wisconsin, and Ohio. The Northeast has twice the hunter density of the Midwest and Southeast and ten times that of the West. Venison is a lean protein, and where deer are plentiful, hunting can be a sustainable way to keep numbers in check.

  In suburbs, managers weigh lethal and nonlethal tools. Extended hunting is the most common in the U.S., and state agencies such as Maryland's set bag limits based on deer counts. For the 2015-2016 season, some areas allowed only antlerless deer, which encouraged culling of does. Sharpshooting by professional marksmen costs more but suits places unfit for public hunting, and it requires a plan submitted to the city. Trapping followed by euthanasia is controversial because of the stress on trapped deer.

  Nonlethal options include contraceptive injections, sterilization, and translocation. Critics say fertility control cannot supply meat, loses effect as open-field populations move, and does nothing for the present herd's grazing. Translocation is costly, stresses deer, risks their deaths, and could spread chronic wasting disease.

  The bills are large. The National Agricultural Statistics Service reported losses to field crops, nuts, fruits, and vegetables of near $765 million in 2001. Deer jump fences easily, and their fear of scare tactics fades quickly. Some crops, especially corn and orchard fruit, have become nearly impossible to grow in places without burdensome deterrents.

  Deer-vehicle collisions in the United States rose from 200,000 in 1980 to 500,000 in 1991. By 2009, the insurance industry estimated 2.4 million collisions over the previous two years, with damage above 7 billion dollars and 300 human deaths. Even so, annual deer mortality from collisions in a two-year Virginia study never passed 20% of the estimated herd. Fences and road under- or over-passes cut collisions but cost a great deal, and lower winter speed limits may be impractical.

  Deer farming has grown into a substantial livestock sector, supplying venison, velvet antlers, hides, and breeding stock. Breeding farms focus on genetics and stock sales, and hunting ranches raise animals for guided hunts. Strict rules require tall, reinforced fencing to keep farmed deer from mixing with wild ones.

  The deer also serves as a symbol. It is the state animal of Arkansas, Georgia, Illinois, Michigan, Mississippi, Nebraska, New Hampshire, Ohio, Pennsylvania, and South Carolina. A buck caps the coat of arms of Vermont and appears on its flag and in stained glass at the State House. It is the national animal of Honduras and Costa Rica and appears on the Costa Rican 1,000 colón note. The 1942 Disney film Bambi changed its hero from the novel's roe deer into a white-tailed deer.

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• 8. Disease and Warming

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  In 2019, confirmed and probable Lyme disease cases in the United States totaled about 35,000. White-tailed deer are the primary host for the adult black-legged tick, Ixodes scapularis, which transmits the Lyme bacterium to humans. The deer themselves cannot be infected by it. The white-footed mouse is the most significant reservoir of Borrelia burgdorferi. Lyme incidence appears to track deer density in the eastern United States, and it runs highest from Maine to Virginia and in Minnesota and Wisconsin.

  Deer also host ticks that transmit Rocky Mountain spotted fever, Rickettsia parkeri rickettsiosis, and human monotropic ehrlichiosis. More deer means more transmission of tick-borne diseases to people, livestock, and other deer.

  In 2021, blood samples gathered by USDA researchers showed that 40% of sampled white-tailed deer carried SARS-CoV-2 antibodies. The highest shares were 67% in Michigan and 44% in Pennsylvania. A later study by Penn State University and Iowa wildlife officials found that up to 80 percent of Iowa deer sampled between April 2020 and January 2021 had active infections. The National Veterinary Services Laboratory confirmed the results.

  The findings raised the possibility that deer had become a natural reservoir for the virus, a potential variant factory that could send new forms back to people. An Ohio State University study showed that humans had passed the virus to deer on at least six separate occasions, and the deer carried six mutations uncommon in humans at the time. Infected deer shed virus in nasal secretions and feces for five to six days. Behaviors such as nose nuzzling, polygamy, and shared salt licks aid its spread.

  Canadian researchers studying Ontario deer in November-December 2021 found an entirely new variant. It had also infected a person in close contact with local deer, potentially the first deer-to-human transmission.

  Climate change is reshaping the whitetail's world. Cold, harsh winters have long kept the species from moving north, so warming lets it advance. A study by Dawe and Boutin found that between 1980 and 2000 the presence of whitetails in Alberta, Canada, was driven mainly by climate. Another study, by Kennedy-Slaney, Bowman, Walpole, and Pond, found that if current CO2 emissions stayed the same, whitetails could survive farther north by 2100. In Alberta, gray wolf populations rose as the deer moved north.

  Warming also helps the pests. Hemorrhagic disease, epizootic hemorrhagic disease, and bluetongue viruses spread by biting midges, which thrive in hotter summers, longer droughts, and heavier rains. Insects that once died at the first snowfall may live longer. Ticks develop faster in heat, and 18 species of tick infest white-tailed deer in the United States alone.

  Deer are also common definitive hosts of the brainworm Parelaphostrongylus tenuis, called meningeal worm, and the giant liver fluke Fascioloides magna. A deer can carry an adult brainworm for years with little or no sign of illness. Moose and elk are dead-end hosts, where the parasite lodges in brain tissue, causes severe neurological disease, and leads to death or a higher chance of being killed by predators.

  As snow packs thin, deer move into places such as northern Minnesota, where winters were once too harsh for large herds, and they carry these parasites to winter-hardy moose. Deer density, climate, and temperature set the level of transmission. In northeastern Minnesota, the 1854 Treaty Authority monitors brainworm and liver fluke infection in deer, and it advises the Minnesota DNR on management decisions in the 1854 Ceded Territory.

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