Spotted Coats: Deer's Warning Sign

A deer with a spotted coat is usually a young deer, known as a fawn. They are born with a dark red coat that helps them merge with the forest floor, also covered in brown and green hues. The white spots on their coat reflect the sun's rays to keep them cool in hot weather and help them remain hidden from predators. The spots also allow the mother to identify her fawn from afar. As the fawn grows, its behaviour and diet change, and it becomes more active and explores its surroundings, so it no longer needs to rely on its camouflage. The spots usually disappear between three and four months of age, and the coat becomes a uniform reddish-brown colour.

Fawns' spots help them camouflage

Fawns, or baby deer, are born with approximately 300 white spots on their backs and flanks. These spots are arranged in two lateral lines along the spine, from the ears to the tail, with the rest distributed randomly on the body.

The spots are not just decorative—they serve a critical function as a form of camouflage. The spots mimic patches of sunlight that shine through trees and other plants, blending in with the varied hues of the forest floor. This helps fawns stay hidden from predators such as bears, coyotes, and bobcats.

In addition to their spots, fawns have other ways of staying hidden from predators. For the first few weeks of a fawn's life, its mother will only reappear to feed it or lead it to a new shelter. The mother's absence helps to mitigate the risk of attracting predators to her more easily detectable scent.

Fawns also have the ability to reduce their heart rate by up to three times when they sense danger, making them almost undetectable to predators.

By the time fawns are around three to four months old, they lose their spots and are able to escape predators by running away rather than hiding.

The spots also help fawns regulate their body temperature

The white spots on a deer's coat help the animal regulate its body temperature. In hot weather, the white spots reflect the sun's rays and keep the deer cool. In colder temperatures, the dark areas of the coat absorb heat and help keep the deer warm. This mechanism is part of the deer's coat design, which serves both as a means of thermoregulation and camouflage.

The thermoregulatory function of the deer's coat is evident in the different characteristics of the summer and winter coats. The summer coat, which appears reddish due to thin, reddish-brown hair, allows deer to cope with heat stress. This coat is only around 0.04 to 0.18 inches deep, facilitating maximum heat loss. On the other hand, the winter coat is made up of longer, brownish-grey hair and is about 5 to 6 times deeper than the summer coat. The depth of the winter coat is critical for the deer's survival, as the deeper coat traps more insulating air, providing protection from the cold.

The colour of the deer's coat also plays a role in thermoregulation. The coat colour tends to be darker in forested areas, where there is less direct sunlight, and lighter in agricultural areas, where deer are exposed to more sunlight. This variation in colour helps the deer regulate its body temperature depending on the amount of sunlight it receives.

The spots on a deer's coat, particularly in fawns, serve multiple purposes. In addition to thermoregulation, the spots provide camouflage, breaking up the outline of the deer's body and making it harder for predators to spot. The spots also mimic sunlight rays filtering through leaves and tree branches, further helping the deer stay hidden. Moreover, the unique spot pattern allows the mother deer to identify and recognise her fawn from a distance.

Piebald deer are deer with a spotting pattern

Piebaldism is a rare genetic mutation that causes random patches of skin to lack the specialized pigment cells that give deer hair its colour. The word "piebald" comes from the magpie's black and white plumage and "bald" in the obsolete sense, meaning "streaked with white". This mutation is different from albinism, where the deer has the pigment cells but lacks the gene to produce colour, resulting in a completely white deer with pink eyes, nose, and hooves. Piebald deer can have varying amounts of white hair, with some being almost pure white except for small patches of regular brown hair, while others have mostly brown hair with patches of white.

Piebald deer are born with a rare genetic condition that can cause skeletal deformities, ranging from mild to severe. Some of the genes that cause changes in coat colour also control other physical traits, and as a result, some piebald deer are born with physical abnormalities such as crooked legs, hooves, and spine, a shortened face, a humped nose, and dwarfism. Adult piebald deer that are seen by hunters usually have milder forms of the condition, as deer born with severe deformities often only live for a few hours or days.

Piebaldism is a recessive genetic trait, and both parents must carry the recessive gene for there to be a chance of producing piebald fawns. It is possible for a piebald doe to reproduce and bear normal fawns, and a normal doe can give birth to both normal and piebald fawns in the same litter. Piebald deer are extremely rare, with less than two percent of all white-tailed deer being piebald, and some researchers claiming this number to be less than 0.02 percent.

Deer coats change colour depending on the time of year

The summer coat is thin, helping deer cope with heat stress. The winter coat, on the other hand, is made up of two layers. The outer guard hairs are hollow, stiff, and about 2 inches longer than the undercoat. The inner layer is soft and dense, providing insulation from cold weather and snow.

The colour of a deer's coat also varies depending on its habitat. In forested areas, deer coats tend to be darker, while in agricultural areas with more direct sunlight exposure, their coats are lighter.

The coat colour of deer serves two main purposes: thermoregulation and camouflage. The white spots on a fawn's coat, for example, help to regulate its body temperature. The white spots reflect the sun's rays, keeping the fawn cool in hot weather. Conversely, the dark areas of the coat absorb heat, providing warmth during colder months.

The spots on a fawn's coat also act as camouflage, breaking up the outline of their body and making it harder for predators to spot them. The spots mimic sunlight rays filtering through leaves and tree branches, further helping the fawn remain hidden in the forest. As the fawn matures, its coat gradually loses these spots, becoming a more uniform reddish-brown colour.

Deer moulting is affected by photoperiod

During the spring and summer months, when the days are longer, deer moult their thicker winter coats to grow a thinner, reddish summer coat. This process is controlled by the photoperiod and usually begins on the head of the deer, progressing downwards until the hind legs shed their winter coat last. The entire moulting process occurs within a few weeks, but the timing and rate can vary depending on the deer's health condition. Generally, healthier deer tend to moult earlier and faster than those in poor condition.

As the days grow shorter in the autumn, deer start moulting their reddish summer coat, which turns into a faded grey or brown colour. This moulting process is triggered by hormonal changes in response to the changing seasons. The new winter coat, which starts growing around this time, is made up of two layers: an outer layer of hollow, stiff guard hairs that are about 2 inches longer than the undercoat, and a soft, dense inner layer that insulates the deer from the cold weather and snow.

The photoperiod not only affects the timing of moulting but also influences the coat colour. Deer coats tend to be darker in forested areas, where there is less direct sunlight, and lighter in agricultural areas, where they are exposed to more sunlight. This variation in coat colour helps with thermoregulation and camouflage, ensuring the deer's survival in different environments.

While moulting in deer is primarily influenced by photoperiod and hormonal changes, other factors such as diet and behaviour can also play a role. As deer grow and their behaviour and diet change, the loss of spots on their coat can occur. Additionally, the growth of antlers in male deer is another physical change that coincides with the change in fur coloration.

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