DEER: CHARACTERISTICS, SUBSPECIES, REPRODUCTION, FEEDING - BIOLOGY - 2025

The deer or deer are placental mammals that make up the family Cervidae. The main characteristic of this clade are the antlers; These bony structures are present in all deer except the Chinese water deer (Hydropotes inermis inermis).

Another characteristic of antlers is that only the males have them, except in the case of the species of the genus Rangifer, where both sexes have antlers. These grow from pedicels, located on the frontal bone. In addition, they are covered with a special fabric called velvet, which is highly vascularized and innervated.

Deer. Source: USDA photo by Scott Bauer

The Cervidae family is very extensive, with a total of twenty-three genera and forty-seven species, which are grouped into three large subfamilies: Hydropotinae, and Capreolinae.

Evolution

Pampas deer (Ozotoceros bezoarticus) Sources: Scott Presnell / Public domain

According to research, the ancestors of the deer lived in the Eocene and lacked antlers, but had fangs. Experts suggest that the evolution of the Cervidae family occurred in stages and lasted for around 30 million years.

Eocene epoch

Ruminants, ancestors of the Cervidae, are believed to have evolved from Diacodexis, which lived between 50 and 55 million years ago in North America and Eurasia.

Its body was around 50 centimeters long and it had a long tail. On each limb it had five fingers, with the peculiarity that the third and fourth were elongated.

Oligocene epoch

In the second half of the Oligocene, the European Eumeryx and the North American Leptomeryx appeared. The latter had the appearance of bovids, but their teeth were similar to that of modern deer.

Miocene epoch

Fossil records suggest that the first members of the superfamily Cervidae lived in the Miocene, in Eurasia. According to research, the first deer with antlers are Dicrocerus, Heteroprox and Euprox.

In this period, the Tethys Ocean disappeared, giving way to vast grasslands. This provided the deer with abundant highly nutritious vegetation, allowing it to flourish and colonize other areas.

Pliocene epoch

Bretzia was one of the three known genera (Bretzia, Eocoileus, Odocoileus) as one of the evolutionary radiation of cervids that occurred in the Pliocene. This happened after the initial immigration from Asia to North America, during the Miocene-Pliocene boundary.

Bretzia was similar in size to mule deer (O. hemionus), but had differences in postcranial skeleton, teeth, and antler and skull morphology.

As for the pedicles of the antlers, they are further apart than in most cervids. In this genus, the antlers have a webbed structure. Deer arrived in South America in the late Pliocene, as part of the Great American Exchange, through the Isthmus of Panama.

Pleistocene epoch

Large antler deer evolved in the early Pleistocene. In this sense, the genus Eucladoceros were comparable, in size, to modern elk. One of the genera that included large species was Megaloceros, which lived in Eurasia in the late Pleistocene.

characteristics

Chinese water deer (Hydropotes inermis inermis). Source: William Warby / Public domain

In general, the members of the Cervidae family have a compact body and a short tail. Its limbs are long and muscular, suitable for the rocky and woody terrain where it lives.

In relation to the skull, deer are characterized by lacking a sagittal crest and by having a postorbital bar. The vast majority have a facial gland, located near the eye.

It contains a substance called pheromone, which can be used to mark the territory. Males secrete this strong essence when they are irritated or excited.

These mammals have excellent night vision. This is because they have a tapetum lucidum, which is a membranous layer located between the optic nerve and the retina. Its function is similar to that of a mirror, since it reflects the light rays that fall on it.

Thus, the available luminosity increases so that the photoreceptors can better capture the environment. In this way, vision in low-light conditions, such as at night in the woods, improves significantly.

- Size

Deer exhibit wide variation in physical dimensions. Also, males are generally larger than females.

The smallest deer is the southern pudú (Puda puda), reaching a height of 36 to 41 centimeters and a weight that ranges from 7 to 10 kilograms. The largest species is the moose (Alce alce), which could measure up to 2.6 meters tall and weigh up to 820 kilograms.

- teeth

The vast majority of deer have 32 teeth. However, reindeer have 34 teeth. The characteristics of the upper canines vary, depending on the species.

Thus, in the Chinese water deer, muntjac deer, and tufted deer, these teeth are elongated, forming sharp tusks. In contrast, other cervids lack canines or are vestigial.

As for the cheek teeth, they have growing enamel ridges, which allow grinding the plant material they consume. Cervids do not have upper incisors, but they do have a hard palate.

The front part of the upper jaw is covered by a hardened tissue, against which the canines and lower incisors are occluded.

- Fur

The fur has a coloration that varies between brown and red. However, the tufted deer has chocolate brown hair and the elk has grayish hair. Also, some species have white spots, such as fallow deer, chital and sika.

Deer have two molts a year. Thus, the red and fine fur that the red deer has during the summer is gradually replaced until in autumn it has a dense and grayish-brown color.

- Antlers

All species of deer have antlers, with the exception of the Chinese water deer (Hydropotes inermis inermis). Also, all males have antlers, except the reindeer.

These structures grow from pedicels, which are bony supports located on the sides of the frontal bone. Initially, the antlers emerge as soft tissues, known as velvet antlers.

Then, these are progressively hardened, due to a process of mineralization and blockage of the blood vessels. Thus, they become hard bone horns.

The velvet, or skin covering, is rich in blood vessels and nerve endings. At the moment that the antlers reach their maximum size, the velvet dies and is shed as the animal rubs them against the vegetation.

The sutures responsible for holding the antlers to the deer head are decalcified annually. This causes the antlers to fall off, usually in late fall or early winter.

Before long, they begin to grow again. In this stage, the expanding bone is covered with a thin layer of skin, which performs a protective function.

Shapes

Because growth is not limited to the base, as in horns, antlers have growth patterns specific to each species. Thus, they can vary from having a simple spike shape, as in the case of muntjacs, to being large and branched structures, as occurs in elk.

Regarding this aspect, some antlers are webbed, while those of the pudu are simple quills. Others have a series of teeth, which emerge upward, from a curved main beam.

In relation to size, the common fallow deer (Gama gama) and reindeer have the heaviest and largest antlers, while the tufted deer have the smallest. As for the lightest, in relation to their body mass, the pudu has them.

Utility

In deer, antlers are one of the most prominent male secondary sexual characteristics. Among its main functions is to guarantee reproductive success and to be a combat element between males.

The antlers are correlated with the hierarchy that the cervid occupies within the group. In this sense, the heavier they are, the higher the position of the animal within the group. Also, experts point out that a male with large antlers tends to be more dominant and aggressive than the rest of the males.

On the other hand, the moose that inhabit Yellowstone National Park, use antlers to protect themselves against the attack of wolves.

Taxonomy and subspecies

Red deer. Source: Tim Felce (Airwolfhound) / Public domain

-Animal Kingdom.

-Subreino: Bilateria

-Filum: Cordate.

-Subfilum: Vertebrate.

-Infrafilum: Gnathostomata.

-Superclass: Tetrapoda.

-Class: Mammal.

-Subclass: Theria.

-Infraclass: Eutheria.

-Order: Artiodactyla.

-Family: Cervidae.

-Subfamily: Capreolinae.

Genres: Moose, Rangifer, Blastocerus, Pudu, Capreolus, Ozotoceros, Hippocamelus, Odocoileus, Mazama.

-Subfamily: Cervinae.

Genres: Cervus, Rusa, Dama, Rucervus, Elaphodus, Przewalskium, Elaphurus, Muntiacus.

-Subfamily: Hydropotinae.

Genus: Hydropotes.

Habitat and distribution

Pudú (Pudu mephistolephis). Source: Eider Joselito Chaves / Public domain

- Distribution

Cervids are widely distributed on all continents, except in Antarctica, Australia, and in much of Africa, where only the Barbary deer subspecies (Cervus elaphus barbarus) exists, north of Tunisia and Algeria.

North America

The largest concentration of deer in North America is in Canada, the Columbia Mountains, and the Rocky Mountains. There are a number of national parks in the British Columbia region, including Mount Revelstoke National Park, Yoho National Park, Glacier National Park, and Kootenay National Park.

In Montana and Alberta, deer inhabit Banff National Park, Glacier National Park, and Jasper National Park.

Eurasia

The Eurasian continent, including the Indian subcontinent, has the largest deer populations in the world. Some species that have traditionally been associated with Europe, such as the red deer, fallow deer and corozos, currently also live in Asia Minor, in Iran and in the Caucasus mountains.

In Europe, cervids are found in the Scottish Highlands, the wetlands between Hungary, Austria and the Czech Republic, and in the Austrian Alps, among others.

Furthermore, they are found in some national reserves, such as the Doñana National Park (Spain), the Białowieża National Park (Poland), the Veluwe in the Netherlands and the Ardennes (Belgium).

In Asia, deer are distributed in coniferous mountain forests, mixed deciduous forests and the taiga, which borders Manchuria (China), North Korea and Ussuri (Russia). The Asian caribou live in the northern fringes of these regions, along the entire Russian-Chinese border.

- Habitat

Deer inhabit diverse ecosystems, ranging from the tundra of Greenland and Canada to the rainforests of India. Thus, they inhabit deciduous forests, meadows, wetlands, arid scrub and alpine areas.

Some species prefer ecotones, in transitional areas between shrubs and forests and between savannas and grasslands. Other cervids live almost exclusively in grasslands, mountains, humid savannas, swamps, and in riparian corridors surrounded by deserts.

Small species of deer and pudúes from South and Central America, in addition to the muntjacs from Asia, generally inhabit dense forests, avoiding open spaces.

Likewise, various deer are circumpolarly distributed, both in Eurasia and North America. For example, the caribou lives in the taiga and the Arctic tundra.

In the habitats of the mountain slopes, they live both in forests and in subalpine dry forests. The forest caribou is found in a more restricted range, between the subalpine meadows and the alpine tundras.

As for the elk, they range in the lowlands of the river valley. White-tailed deer have expanded their range to the bottoms of river valleys and foothills of the Rocky Mountains in Canada.

State of conservation

Moose (Alces alces). Source: Donna Dewhurst / Public domain

Within the extensive family Cervidae, there are numerous species in danger of extinction, because their populations are threatened by various factors, thus causing their decline.

A total of 56 deer have been listed by the IUCN as at risk of extinction. Among these, one is extinct, Rucervus schomburgki, and another, Elaphurus davidianus, no longer lives in wild conditions.

Within the group of least concern, 3 are slightly threatened, 16 are vulnerable, 7 are in danger and 2 are in a critical state of extinction. Within the group, 10 cervids do not have sufficient data for their evaluation.

- Threats and actions

The main threats to deer include their hunting and competition with other animals for food resources. Another factor that affects these mammals is the loss of their habitat, due to the felling of trees and the use of land for agriculture.

Likewise, climate change causes some species to leave their home ranges and move towards the poles. An example of this is the moose, located in the north central United States.

A demographic study carried out in the 1980s reveals a decrease in its southern population, in response to the increase in temperature in that region.

The various threatened species are protected in nature reserves and national parks. In addition, 25 cervids in danger of extinction are included in Appendix I of CITES.

Reproduction

Puberty in deer occurs around 16 months of age and after this stage, they exhibit seasonal polyester. As for the estrous cycle, it can vary between 17 and 22 days, depending on the species.

This can continue to appear cyclically for up to six months, in the event that the female has not been fertilized. The vast majority of deer are polygamous, however, some species are monogamous, such as the European roe deer.

In some species, males may mate with females whose territories are within their own. Also, these could move between herds, in search of females in heat.

For their part, the females form small groups, called harems, which are protected by the males. They exercise their dominance over the harem, challenging rival males.

Courtship behavior in cervids is characterized by the closeness between the pair, with licking and sniffing of the ano-genital area. Also, the male tends to chase the female and be aggressive towards other males. The length of gestation varies according to the species, however, it has an average of 7 months.

Seasonal mating

Members of the Cervidae family are seasonal breeders. Variations related to rainfall, temperature and the length of the day influence the mating season.

In those climates where the changes in the seasons are extreme, the length of the day is used to time the mating period.

Experts point out that deer respond reproductively better on short days than long ones. This means that estrous behaviors begin to show in late September and October and not during the summer season.

Seasonality in the male

Mating is controlled by melatonin levels. This is a modified hormone, which is released by the pineal gland. In seasons where there are fewer hours of light per day, testosterone levels increase.

This could influence the volume and pH of seminal fluid, as well as the motility and concentration of the sperm. Due to this, in the period when the male is more sexually aroused, the quality of the semen is much higher.

Seasonality in the female

Heat in females is triggered by the decrease in the photoperiod. In this sense, the pineal gland produces melatonin, in response to the low light of the environment.

Seasonal changes in fertility are associated with the secretion of luteinizing hormone-releasing hormone (LHRH) from the hypothalamus. In turn, this hormone influences the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary.

Feeding

Deer are herbivorous animals that feed primarily on leaves. These select the most digestible parts of the plant, such as young leaves, fresh herbs, fruits, flowers, lichens, and fresh herbs.

This is why they are considered concentrated selectors, since they have a tendency to choose the most nutritious parts of plants. However, some species are classified as intermediate.

This feeding behavior is contrary to that of cattle and sheep, who consume large amounts of low quality fibrous feed.

The dietary requirement of cervids includes a large amount of minerals, such as phosphate and calcium, which contribute to the growth of antlers. This is why some species such as red deer that live on the island of Rum, do not only eat vegetables.

Within their diet they usually consume the offspring of some seabirds and their eggs. Specialists point out that this may be due to the mammal's need to recover mineral elements that plants do not contain.

Factors

Deer feeding is mixed, between browsing and grazing. In addition, it depends on the seasons and the habitat where it is found. Thus, during winter and spring, their diet is made up of 75% herbaceous. In autumn and summer, increase the consumption of fruits and woody plants.

Furthermore, in cervids, food intake is influenced by the nutritional value of the forage, the photoperiod and the stage of the reproductive cycle.

Likewise, body condition also undergoes variations related to changes in the seasons. In late summer, a deer body stores a large proportion of fat. This will be used by the males during their fall routine.

As for females, they use fat stores gradually in winter and early spring. This allows them to maintain an adequate body condition in the first two trimesters of pregnancy, when food resources are limited in the environment.

On the other hand, the reduction in appetite suffered by deer in winter and autumn helps to avoid the energy expenditure caused by the unproductive search for food sources at those times of the year.

Behavior

Cervids are generally classified as twilight animals, although some species are usually active for much of the day. These animals tend to become more aggressive in situations of food shortage and during the mating season.

Aggressive males, larger in size and with larger horns, tend to dominate the rest of the males. This guarantees them access to the females in heat during the breeding season. In the fighting between males and males, they can use their antlers.

Also, they could walk around each other, surrounding each other, while vocalizing a high-pitched moan or low growl. Deer often lift body hair, by contracting the retractor pili muscle, making it appear larger.

In the mating season, males use their forelimbs to scrape the ground, thus announcing their presence and willingness to mate. Occasionally they may urinate or deposit their stool on the scraped area.

Regarding the social organization of cervids, it is variable and could be influenced by the season. Although the vast majority of species form small groups, to feed they could be grouped in large herds. Once the objective is achieved, they disperse.

References

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4. Stefany Gomez (2018). Cervidae: deer, elk, and moose. Recovered from cvm.msu.edu.
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