Black-tailed deer, scientifically known as Odocoileus hemionus, are a subspecies of mule deer that inhabit the Pacific coast of North America. Graceful and adaptable, they play a crucial role in their ecosystems. Understanding their diet and foraging habits is key to appreciating their ecological significance and managing their populations. This article delves into the specifics of what black-tailed deer eat, how they find their food, and how their feeding habits influence the environment.
Geographic Distribution and Subspecies
The black-tailed deer thrives along the Pacific coast, ranging from western California up through Alaska. Their prevalence extends through western Oregon, Washington, coastal and interior British Columbia, and into the Alaskan panhandle. Within this range, two primary subspecies are recognized: the Columbian black-tailed deer (O. h. columbianus) and the Sitka black-tailed deer (O. h. sitkensis). The Columbian black-tailed deer occupies regions from northern California to British Columbia, while the Sitka black-tailed deer is specifically adapted to the wet coastal rainforests of Southeast Alaska and coastal British Columbia.
Habitat Preferences
These deer are edge-adapted species, often found in areas where forests meet open meadows. They are particularly common on the edges of forests where there is adequate shelter and ample meadowland. This preference for edge habitats allows them to utilize the dense forest cover for hiding and the open areas for feeding, especially at dawn and dusk. They typically spend their entire lives in areas less than 7.8 square kilometres and do not migrate long distances, though mountain-dwelling deer may seek lower elevations in winter. Black-tailed deer are often found in clearings caused by forest fires or logging, as they prefer a mix of dense forest cover and open areas.
General Dietary Habits
Black-tailed deer are herbivores, and their diet varies depending on the season and the availability of food sources. As herbivores, black-tailed deer convert plant matter into a form that higher trophic levels in the food chain can consume. They are browsers, meaning they primarily feed on leaves, twigs, and shoots of trees and shrubs, as well as grasses and forbs. Their diet reflects their habitat, consisting of a wide variety of plants found in the coastal woodlands of the Pacific Northwest.
Seasonal Diet Variations
The diet of black-tailed deer changes significantly throughout the year, adapting to the changing availability of different plant species.
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Winter and Early Spring
During the winter and early spring, when many plants are dormant or covered in snow, black-tailed deer rely on evergreen vegetation. Key components of their diet during this time include Douglas fir, western red cedar, red huckleberry, salal, deer fern, and lichens growing on trees. These provide essential nutrients when other food sources are scarce.
Late Spring to Fall
As the weather warms and plants begin to grow, the diet of black-tailed deer expands to include a wider variety of vegetation. Late spring to fall, they consume grasses, blackberries, apples, fireweed, pearly everlasting, forbs, salmonberry, salal, and maple. These provide the deer with the energy needed for growth, reproduction, and building up fat reserves for the winter.
Specific Food Preferences
While black-tailed deer consume a wide range of plants, they do have some specific preferences. They are known to browse on western poison oak, despite its irritant content. This adaptability allows them to utilize a food source that many other animals avoid.
Foraging Techniques
Black-tailed deer are often spotted grazing in mountain meadows at dawn and dusk. They are selective foragers, carefully choosing the most nutritious and palatable plants available. Their foraging habits are influenced by the availability of food, the presence of predators, and the nutritional needs of the deer at different times of the year. Scouting (for scat, rubs, scrapes) and knowing their habits are key for harvesting a secretive blacktail in its dense habitat.
Impact on the Ecosystem
Black-tailed deer play a significant role in shaping the vegetation in their habitat through their browsing and feeding habits, influencing the composition and structure of plant communities. This, in turn, impacts the other species that depend on those plants. Healthy black-tailed deer populations indicate a balanced ecosystem because the availability of food plants and predator populations influence their numbers.
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Positive Impacts
Their carcasses also provide food for scavengers like wolverines, ravens, and magpies. By consuming plant matter, they help to cycle nutrients through the ecosystem, making them available to other organisms.
Negative Impacts
However, an overabundance of black-tailed deer can, at times, negatively impact ecosystems by over browsing and reducing plant diversity, which can harm some species. Overgrazing can lead to a decline in plant diversity and alter the structure of plant communities.
Predators and Their Influence
Black-tailed deer are telling of the balance in the ecosystem. If there is not enough vegetation, the deer population cannot survive, leaving predators hungry. If there are not enough predators, there may be too many deer, causing over-grazing. Several predators play a role in regulating black-tailed deer populations.
Current Predators
- Coyotes (Canis latrans) - Coyotes are a historic and current predator of black-tailed deer, though they mostly target the weak, young, or starving deer.
- Cougars (Puma concolor) - Cougars are the only other major predator of black-tailed deer currently present in their habitat.
- Bears (Ursus spp.) - Both black bears (Ursus americanus) and grizzly bears (Ursus arctos) are known to prey on Sitka black-tailed deer, though the impacts of this predation are unstudied.
- Golden eagles (Aquila chrysaetos) - Golden eagles are also a common predator of black-tailed deer.
Historical Predators
- Wolves (Canis lupus) - The grey wolf was a major historical predator of black-tailed deer throughout their range but has been absent from the region for over a century.
Reproduction and Fawn Survival
Reproduction is a key component driving deer population growth across deer and other ungulate species- most variation in year-to-year population growth is driven by differences in fawn survival among years, not differences in female survival or pregnancy rates. Sitka black-tailed deer typically have 1-2 fawns, conceived during their 2nd fall ad born when they are just turning 2 years old. Pregnancy rates are typically high, even in populations with less high-quality forage available, but twinning rates are lowered when food is scarce. Twinning rates are also lower for first-time mothers, who typically have a "singleton" instead.
Conception typically occurs mid-November, but if does do not conceive during their first estrus cycle (if they are first-time breeders, or if severe weather disrupts the rut), fawns may not be conceived until December or even, in rare cases, January. As a result, while the "peak" of fawn season occurs from late May through mid-June, fawns can be born later in the summer as well, all the way into August. These late-born fawns can do just fine in mild winters, but are much more likely to die in sever winters with deep snow and/or long cold spells. This is because they are lighter-weight and smaller, and cannot move through deep snow as well as larger, stronger fawns. We found that in a harsh snow winter, 85% of fawns did not survive until 1 year of age.
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Similarly, fawns that are born lightweight are more vulnerable to bear predation, although bears will also eat normal-weight fawns. Black bears on Prince of Wales Island eat ~40% of fawns over the course of the summer. Female deer with fawns face some tough trade-offs- they have some very high nutritional demands through late pregnancy and while they are lactating (in fact, lactation requires just as many calories per day as the end of pregnancy), but they also need to keep their fawns safe from black bears, and keep themselves safe from wolves and bears as well. As a result, we see them change their behavior through the spring, summer, and fall. As they become increasingly pregnant and birth nears, they go from not caring much about where black bears are on the landscape, to actively avoiding areas of high black bear occurrence. Once fawns are born, they continue to avoid black bears, but start to relax a bit as their fawns get older and allow more overlap with black bears in space. If their fawns die, they quickly return to no longer caring about black bears, instead focusing intensively on finding areas with lots of forage. Bear diets on Prince of Wales consist of 10-20% deer in springtime, which we think is mostly due to predation of fawns. Once deer reach adulthood, they face new challenges.
Human Interactions and Management
Black-tailed deer are an important game species, and their populations are managed to ensure sustainable hunting opportunities. Understanding their diet and foraging habits is crucial for effective management strategies. Scouting (for scat, rubs, scrapes) and knowing their habits are key for harvesting a secretive blacktail in its dense habitat. Scent control is important for hunting.
Adaptations
Black-tailed deer have several adaptations that allow them to thrive in their environment. Their smaller size and darker coloration compared to mule deer help them to blend in with the dense forests they inhabit. They also have excellent sight and smell. Their large ears can move independently of each other and pick up any unusual sounds that may signal danger. Deer communicate with the aid of scent and pheromones from several glands located on the lower legs. The metatarsal (outside of lower leg) produces an alarm scent, the tarsal (inside of hock) serves for mutual recognition and the interdigital (between the toes) leave a scent trail when deer travel.
Interesting Facts
- Columbian black-tailed deer have an average lifespan of 9-10 years in the wild and 17-20 years in captivity.
- Sitka black-tailed deer have an average lifespan of about 10 years, with some living up to 15 years.
- Black-Tailed deer are excellent swimmers.
- Blacktail deer may be the park's most graceful mammal. They are much smaller than Roosevelt elk, and may be seen just about anywhere within Olympic National Park, from subalpine forests and meadowlands down to river valleys.