American Bison

Taxonomy

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Artiodactyla

Family: Bovidae

Genus: Bison

Species: American bison

Evolution 

The American Bison, has several recognized subspecies.

Bison bison bison (Plains Bison)

Bison bison athabascae (Wood Bison)

The American Bison species has been in existence for thousands of years. Fossil records indicate that bison have roamed North America for at least 10,000 years.

The closest living relative to the American Bison is the European Bison (Bison bonasus). Both species belong to the same genus, Bison, and share a common ancestry.

the three ancestors of the American Bison 

Bison antiquus: This species was larger than the current American Bison and lived during the Pleistocene epoch. It is said to be the direct ancestor of the modern bison.

Bison latifrons: Another ancestor of the American Bison, Bison latifrons, also lived during the Pleistocene epoch. It had large, long horns and was bigger then the Bison antiquus.

Bison occidentalis: This species is considered an ancestor to both Bison antiquus and the modern American Bison. Bison occidentalis lived during the late Pleistocene epoch and is thought to have evolved into Bison antiquus.

Physical Description:

The American Bison has a massive and stocky build with a hump on its shoulders and a large head.

It has a shaggy, dark brown coat that appears lighter on the underside.

The fur on its head and shoulders is long and thick, forming a beard and a cape-like appearance.

Both males and females have curved, sharp horns that can grow up to 2 feet long.

Their front hooves are broad and strong, it has adapted for digging through snow in search of food.

Key Characteristics:

American Bison are herbivores, primarily grazing on grasses and sedges.

They are social animals and usually live in herds, with a dominant male  leading the group.

Bison are well-adapted to survive harsh climates, including extreme cold and heat.

They have an amazing sense of smell and hearing, helping them detect predators.

Bison are known for their agility and can run at speeds of up to 35 miles per hour.

Size:

American Bison are one of the largest land mammals in North America.

Height at the shoulder: 5 to 6.5 feet \

length: 7 to 11.5 feet

Height at the hump: up to 6 feet 

Weight:

Adult males (bulls): 900 to 2,200 pounds 

Adult females (cows): 600 to 1,000 pounds

Life Span:

In the wild, American Bison typically live for around 15 to 20 years. However, in captivity, they can live up to 25 years or more.

Differences between Males and Females:

Size: Adult males are larger and weigh more than females.

Horns: Both males and females have horns, but those of males tend to be larger and thicker, while females horns are slightly smaller.

Hump: Bulls have a more prominent hump on their shoulders compared to cows.

Behavior: Bulls often engage in sparring and dominance displays during mating season to establish hierarchy and mating rights.

Description of Habitat 

Rainfall:

The specific amount of rainfall can vary depending on the region, but bison typically inhabit areas with moderate to high rainfall, ranging from roughly 20 to 40 inches per year. They can also adapt to drier environments by seeking water sources like rivers, lakes, or ponds.

Plants:

American Bison graze on various types of grasses and sedges that dominate their habitat. They are feed on coarse and fibrous vegetation, including species such as buffalo grass, blue grama grass, western wheatgrass, and switchgrass. They also consume other plants like herbs and shrubs.

Animals:

The habitat of the American Bison supports a diverse range of wildlife. Some common animals found in their habitat include pronghorn antelope, white-tailed deer, mule deer, elk, coyotes, wolves, prairie dogs, ground squirrels, rabbits, birds such as grouse and sparrows, and various reptiles and amphibians.

Temperature:

The American Bison adapts to varying temperatures. They can withstand extreme cold and heat. In their historic range, temperatures can range from below freezing in winter to hot summers. The specific temperature range varies depending on the region where they are found.

Terrain:

DISTRIBUTION 

American Bison inhabit a variety of terrains, including grasslands, prairies, meadows, and open woodlands. Their habitat often consists of vast, expansive areas with a mixture of open spaces for grazing and areas with cover for protection and shelter, such as hills, valleys, and low-lying areas near water sources.

The American Bison, historically, had a wide distribution across North America. However, due to human activities such as hunting and habitat loss, their range has significantly diminished. Especially during the 1800’s

Continents Found:

The American Bison is native to North America and historically inhabited various regions within the continent. They were found in areas spanning from Canada, through the United States, and into northern Mexico. Today, their distribution is limited to specific regions within North America.

Invasive at All:

The American Bison is not considered an invasive species. They are native to North America and have evolved within the ecosystems of the continent for thousands of years. Human activity, including the introduction of non-native species and alteration of landscapes, can sometimes disrupt the balance of ecosystems and impact native species, including the American Bison.

Diet:

 Like previously stated American Bison primarily graze on grasses and sedges, which make up the majority of their diet. They also consume other plant material such as herbs, shrubs, and even tree bark when necessary.

Feeding Frequency:

Bison are ruminant animals, they have a specialized digestive system that allows them to extract nutrients from plant material. They have a relatively low metabolic rate and can extract nutrients from a single meal for an extended period. Bison typically have a lower feeding frequency compared to some other herbivores. They can go for long periods without eating and often spend a significant portion of their day grazing to fulfill their nutritional needs.

Obtaining Food:

American Bison primarily obtain their food by grazing on grasses and sedges. They use their large, muscular tongue and strong jaws to tear off and consume the vegetation. They feed on grass by using their wide, flat teeth to efficiently break down the plant material.

Special Foods:

While grasses and sedges form the bulk of their diet, American Bison do not have any specific special foods that are exclusive to their diet. During certain seasons or in response to environmental conditions, they may consume a wider variety of plants, including different grass species, herbs, or shrubs. They also adapt their feeding patterns to available food sources and can modify their diet based on local plant availability and nutritional requirements.

Group Structure:

Bison typically live in herds, which can vary in size depending on factors such as habitat availability, food resources, and reproductive dynamics. Herds can range from a few individuals to larger groups consisting of dozens or even hundreds of individuals. The dynamics of herds can change over time as individuals join or leave the group.

Roles within the Community:

A bison herd, there are generally no distinct roles or hierarchy among individuals. During certain periods, such as the mating season, dominant individuals, particularly males, may establish dominance and mating rights through displays of strength and aggression.

Male or Female Led Groups:

Bison herds do not have a specific male or female leader. However, during the mating season, dominant bulls may temporarily lead and defend a group of females, known as a harem, for mating purposes. Outside of the mating season, herds generally do not have a clear leader, and decisions, such as movement and foraging, are made collectively or influenced by environmental factors.

Individuals within the Group:

A typical bison herd consists of individuals of varying ages and sexes. This includes adult males , adult females, and their offspring . Young males may form bachelor groups or associate with the herd until they reach sexual maturity and compete for mating opportunities.

Interactions:

Bison interact with each other through various behaviors, which can include vocalizations, body posturing, and physical contact. They communicate using low-frequency vocalizations, such as grunts, bellows, and snorts. Aggressive interactions, such as head-butting or pushing, may occur during dominance disputes or when defending territories or resources.

Reproduction:

Mating Frequency:

Bison mate once a year during the mating season, also known as the rut. They do not engage in multiple matings throughout the year.

Number of Mates:

Male bison, known as bulls, can mate with multiple females during the mating season. Dominant bulls may form harems, which are groups of females that they guard and mate with exclusively during the rut.

Time of Year for Mating:

The mating season for American Bison occurs in late summer or early fall. The timing can vary depending on factors such as geographic location and climate. During this period, bulls compete for mating opportunities with females, engaging in displays of strength and aggression.

Mating Rituals:

Mating rituals among American Bison involve various behaviors to establish dominance and attract mates. Dominant bulls often engage in displays of dominance, such as head-butting, wallowing in dust or mud, and loud vocalizations. They may also use their horns and size to intimidate rivals and establish their position within the herd.

Number of Offspring:

The gestation period for bison is around 9 months. Females typically give birth to a single calf at a time, although occasionally, twins may be born. After birth, the mother cares for and nurses the calf, which remains dependent on her for several months.

Unique Characteristics of Mating:

One unique characteristic of bison mating is the formation of harems. Dominant bulls gather a group of females, excluding other males from mating with them during the rut. Bulls compete with each other for the chance to establish and defend a harem. The mating rituals can be intense, with bulls showcasing their strength and prowess to assert dominance

Development:

Birth: Calves are born after a gestation period of approximately 9 months. At birth, calves are relatively small, weighing around 40 to 50 pound and are able to stand and walk within a short period of time.

Juvenile Stage: After birth, the calf enters the juvenile stage. Which lasts for a few months to a year, the calf remains dependent on its mother for nourishment and protection. 

Subadult Stage: As the bison matures, it enters the subadult stage. This stage occurs between the juvenile and adult stages and is marked by continued growth and development. Subadults start to exhibit more independence and may begin forming associations with other individuals within the herd.

Sexual Maturity: American Bison reach sexual maturity at different ages depending on various factors such as nutrition and environmental conditions. Generally, females can reach sexual maturity at around 2-3 years of age, while males may reach sexual maturity between 3 and 5 years of age.

Activities and Environment of Stages:

During the early stages of development, calves primarily engage in activities such as nursing, exploring their surroundings, and learning from their mother and other herd members. They gradually start to graze on grass and learn social behaviors within the herd.

As bison grow older, they become more involved in foraging for food, engaging in social interactions, and learning from their experiences within the herd. They spend a significant portion of their time grazing, resting, and moving collectively as a herd.

Dominance and Mating: During the mating season, dominant bulls compete for the opportunity to mate with females, establishing harems and engaging in displays of strength and aggression. Females typically select mates based on the displays and dominance of the bulls.

Difference between the two is already stated previously 

Predation: Historically, bison faced predation from large predators such as wolves and bears. Predation can result in the death of both young and adult bison. it's important to note that the historic predators of bison have been significantly reduced in numbers due to human activities, resulting in a decrease in predation pressure.

Sexual Competition: During the mating season, male bison engage in intense competition for mating rights and dominance. This can lead to aggressive encounters between males, which can result in injuries or even death.

Disease: Bison are susceptible to various diseases and infections, some of which can be fatal. Infectious diseases, such as brucellosis or bovine tuberculosis, can affect bison populations. Additionally, outbreaks of respiratory or gastrointestinal illnesses can impact individuals within a herd.

Harsh Environmental Conditions: Extreme weather events, such as severe winter storms or droughts, can pose challenges to bison survival. Harsh winter conditions can limit food availability, leading to starvation, while droughts can result in water scarcity and dehydration.

Human Interactions: Historically, bison were hunted extensively for their hides, meat, and other resources, which significantly impacted their populations. Although hunting pressure has been regulated in modern times, human activities, such as collisions with vehicles or habitat destruction, can still contribute to bison mortality.

Accidents and Injuries: Bison may face accidental injuries or deaths due to incidents such as falls, collisions, or getting trapped in natural or human-made hazards.

Old Age and Natural Causes: As with most organisms, bison also face mortality due to old age and natural causes. Older individuals may succumb to age-related health issues or simply die of natural causes

Intra-Species Competition 

Food: Bison may compete for access to grazing areas, particularly during periods of limited food availability or in areas with high bison densities. This competition can result in individuals seeking out the most nutritious or abundant forage.

Mating Opportunities: During the breeding season, male bison compete with each other for access to females. Dominant bulls establish harems and guard the females against other males, engaging in aggressive behaviors to assert dominance and secure mating rights.Inter-Species Competition 

Grazing Competition: Bison may compete with other grazing herbivores, such as elk or pronghorn, for access to food resources within shared habitats. This competition can arise when multiple species rely on similar vegetation for sustenance.

Water and Space: Bison may compete with other large herbivores or wildlife species for access to water sources, especially during periods of drought or in areas with limited water availability. They can also compete for space or habitat areas suitable for grazing, resting, and raising calves.

Affect of Invasive Species:

The presence of invasive species can impact the competition dynamics and resources available to American Bison. Invasive plant species, for example, can alter the composition and availability of the vegetation that bison rely on for grazing. If invasive plants outcompete native species, it may reduce the availability of suitable forage for bison.

Invasive predators can also affect the behavior and distribution of bison, altering their interactions with other species and their access to resources. the impact of invasive species on bison can vary depending on the specific invasive species involved and the ecological context of the habitat.

Efforts in wildlife management and conservation aim to control the effects of competition and invasive species by implementing strategies to maintain suitable habitats, manage populations, and restore ecological balance within bison habitats.

IUCN Rating: Near Threatened

Population: The population of American Bison has significantly declined from its historic numbers. By the late 1800s, their population was reduced to a few hundred individuals due to overhunting and habitat loss. Conservation efforts and captive breeding programs have led to population recovery. As of 2021, the estimated population of wild American Bison in North America was around 31,000 individuals. This number does not include bison in captive or semi-captive populations.

Population Trend: The population trend of American Bison has been increasing over the past century, thanks to conservation efforts and reintroduction programs. Efforts have been made to restore bison populations in their historic ranges and establish protected areas. While the population trend is generally positive, it is important to continue monitoring and managing the populations to ensure long-term sustainability.

Impact of Humans:

Humans have impacted American Bison through overhunting, habitat loss, disease transmission, and genetic bottleneck due to population decline.

Potential Future Impacts:

Future impacts may include habitat loss, climate change effects, disease, invasive species, and human-wildlife conflicts.

Interaction with Humans:

Humans have interacted with American Bison for thousands of years, with European settlers initiating extensive hunting and exploitation.

Efforts to Minimize Impacts:

Efforts to minimize impacts include conservation programs, protected areas, sustainable management, and collaborative partnerships among stakeholders.