Trophic Level II - The Herbivores Antelopes Page 22

  Summary

Ruminants that possess hollow horns, like a cow’s, are classed as bovids. Sheep, goats, antelopes and cattle are belong to the family bovidae. (Deer are ruminants but have antlers instead of horns and are not, therefore, bovids.) Worldwide, there are 120 species of bovids and of these, 84 are antelope. There are seventy-five species of bovids found in Africa including 72 different types of antelope. The other three species of bovids found on this continent are the barbary sheep, the ibex and the buffalo.

The Serengeti-Mara has 22 ruminant species, many of which are dealt with in this section.

Shared Characteristics

All bovids share several characteristics:

A) Horns:

All males have horns which consist of a hard, horny sheath which grows over an inner core of bone. Horns grow throughout the animal's life, but are often worn down through use. About three quarters of the species also have horned females. The horns of males are larger than those of females.

The females with the largest horns tend to belong to the most gregarious species. It is thought that this allows them to compete successfully with young males and other females for food. In general, forest dwelling antelopes have smaller horns and often the female lacks them entirely.

Males with horns the same size as the females’ will remain part of the herd, probably because they look like females. There is safety in this as they can live in larger herds where there is a lesser chance of being singled out by a predator. As their horns become larger than the female's, they leave and join bachelor groups.

B) Color:

Shades of brown are the most common colors for ruminants. There are only a few species that are almost white and a few that are predominately black. Sociable species, such as the wildebeest and topi, tend to have either bold markings (topi, Thomson’s gazelle) or they are a solid dark color (wildebeest, kongoni). These qualities make it easy for the antelopes to recognize members of their own species.

Some antelope have stripes that serve to break up their body shape in the bush. Bush buck are an example of this. Others are dull in color and match their surroundings for easy concealment (dikdik).

C) Scent Glands:

Scent glands are found on most ruminants. The complex chemical secretions produced by antelope convey information about the animal’s status, sex, and reproductive state. The most common and the most important glands are the interdigital glands and the preorbital glands. Secretions from the interdigital gland, located between the two toes of the hoof, leave a telltale scent that helps other antelope to follow its path. Preorbital glands are located below the eye. The animal maneuvers a twig or blade of grass so that the tip enters the gland. There, the plant is marked by a globule of black, tar-like "oil" that clearly announces the marker’s intention. This gland is well-developed in antelopes that maintain a territory; dikdiks, klipspringers, impala and Thomson’s gazelle.

Evolution - Form and Function

The antelope family is believed to have evolved from tiny forest dwelling ruminants. These animals lived in pairs and probably ranged over large areas. There was not enough food to support large herds in this environment. Within the Serengeti-Mara region, the dikdik’s existence is probably similar to the lives led by these ancestral antelopes.

As this family moved from being browsers on a few widely separated species of trees, to grazers on a superabundant source of food (grass), they evolved having larger bodies and living in bigger groups.

If these two scenarios are correct, it would be reasonable to expect that between small, forest dwelling antelopes (like dikdik) and large, gregarious ones (like wildebeest) there would be a variety of living arrangements to be seen. In the Serengeti-Mara, this is certainly the case. Bush dwelling impala are found in small herds, sometimes numbering up to 100 animals.

Other Differences

Other differences also exist. Grassland antelopes, besides existing in large herds, have also developed bodies designed for fleeing. They have straighter backs, long legs, large lungs and are generally designed for speed. Forest dwelling antelopes have hunched backs that make it easier to slide under bushes. They are built for quick rabbit-like takeoffs, sharp turns and sudden stops. They are hiders rather than runners.

Grazers tend to have large, wide mouths to take in large amounts of food. Browsers have narrow mouths that allow them to be selective in their choice of leaves and twigs. There are exceptions. The impala can be both a grazer and a browser and have a mouth that is adapted to both functions. Thomson's gazelles have narrow mouths because they select shoots that grow near the ground.

Forest dwellers are usually monogamous and very loyal to their mates (dikdik, klipspringer). Grassland antelope tend to have territorial males that try to corral groups of females for breeding (wildebeest, topi, impala, Thomson's and Grant's gazelles). Reed buck are different. A single male will have a territory overlapping the territory of one or two females.

Water, Water Everywhere (or Not)

Wildebeest must drink water on a regular basis. When long droughts and irregular rainfall create conditions where this is not possible, these animals are not found. Some antelope, however, are drought tolerant. Indeed, some species have almost never been seen to take a drink. They get their moisture from the leaves of plants.

Being drought tolerant means that the animals have to conserve body moisture as much as possible. Below is a list of some ways that Thomson’s gazelles, dikdik and Grant’s gazelles achieve this;

• Rest in shade during the hottest time of the day.
• Line up their bodies with the sun so that sunlight hits the least amount of body area as possible.
• Have a light colored coat to reflect sunlight.
• Feed during the coolest parts of the day.
• Get moisture from plants
• Concentrate urine and absorb moisture from droppings.
• Allow body temperature to rise by up to 6° C (10° F). The excess heat is stored and then slowly used during the cooler nights.
• Pants nasally (unlike a dog’s tongue panting). Nasal panting cools the blood without the loss of body moisture that "normal" panting costs.

Reproduction

African antelopes give birth to one offspring at a time. Twins do occur, but very rarely. Indeed, the only members of the African ungulate group to have several babies at a time are the swine (warthogs, bush pig and giant forest hog).

Gestation time for small to medium-sized antelopes is four to six months. Larger members take up to nine months to give birth.

The antelope of the Serengeti-Mara region have adapted their breeding cycles so that births occur when the food supply is greatest.

The females of the smaller species may breed before they are a year old. Among the species in the mid-size range, most conceive and deliver their first offspring by the time they are two years old. Large species begin to breed a year later.

Males usually first mate a year or two after the females.

Newborns

The young of antelope behave in one of two ways after they are born. They are either "lying-out" babies or they are "followers". Followers go with their mother as she travels or grazes. There is no attempt to conceal themselves when they rest. Followers include the young of wildebeest, topi and buffalo. Sometimes with wildebeest and topi, the mother will graze away from the young as they rest. To an untrained eye this may appear as lying-out behavior but it is not.

True lying-out behavior begins within three to six hours after birth. All baby antelope (and zebra) follow their mothers as soon as they get to their feet and nurse. The young of lying-out species then search for a place to hide. The ideal spot is in a depression and close to a vertical object (i.e., a tree or clump of long grass). Often, only one of these criteria can be met and sometimes neither.

Once the baby is lying-out, the mother will move away from it. Unless discovered by a predator, the calf will lie motionless until its mother returns to nurse it. She may move quite some distance away but she will not be out of sight for very long. When she returns, she does so in an indirect manner. When she is certain that it is safe, she gives a soft call and the calf pops up and goes to feed. Before feeding, the mother licks the baby’s genital and anal regions. licking stimulates it to defecate and also removes any droppings that may cling to the baby’s coat. When it lies down again, it will be virtually odor free.

With followers, a mother and young are never separated very long. Indeed, the calf is most reluctant to let its mother get more than thirty meters (yards) away.

The young of most antelope are often kept in nursery herds. Here, several females bring their babies together and allow them to associate. In some cases, such as eland, the nursery herd is more closely bonded than are the adults. Of the herding species, only Thomson’s gazelles and Grant’s gazelles do not have nursery groups.

Separation from their parent means certain death to all young. Mothers will not nurse any other offspring but their own.

Advantages of Being a Ruminant

Ruminants have several advantages over similar sized herbivores, such as the horses and zebras. They are:

• superior ability to convert cellulose (grass) into digestible carbohydrates
• breakdown of food accomplished by symbiotic microorganisms that digest cellulose by fermentation
• fermentation occurs before gastric digestion in rumen but in hindgut fermenters it occurs in the large intestine and cecum after passing through the stomach
• ruminants digest far more efficiently. Compare, for example, the coarseness of the donkey's droppings

Comparison of the Two Feeding Techniques

The rate of passage is the time it takes for each type to digest its food from the first mouthful of grass to the final disposal of the remaining waste as either dung or urine.

Cellulose Utilization is the amount of vegetation actually used. Ruminants get more out of their food but it takes them longer to gain the value, compared to the hindgut fermenters. In fact, hindgut fermenters are actually able to get more nutritional value than the ruminant over a period of time. This is of no advantage in good pastures but does give them an advantage in drier climates.

In other words, hindgut fermenters derive only 2/3 of the nutritional value that ruminants do BUT they do it in half the time, thus in the time it takes a cow to process her food the donkey gets 1 1/3times the nutritional value!

Rumination Process In Summary

• animal feeds until rumen is comfortably full
• briefly chews each mouthful
• settles down to chew cud (cud is the coarsest plant particles that float on the top of the semi-liquid rumen contents)
• regurgitated a mouthful at a time
• enlarged salivary glands secrete a buffered Ph solution that helps maintain rumen contents
• chewing increases the extraction of nutrients by increasing the surface area exposed to bacteria
• rhythmic contractions stir rumen
• material passes through the next three stomachs where it is absorbed
• a major drawback is that ruminant digestion takes up to four days from ingestion to excretion
• when the protein count falls to less than 6%, food cannot be processed fast enough to maintain weight. Starvation may occur if the animals do not find new sources of food.

Consequences of Body Size:

Ruminants are all over 3 kg (6.6 lb.) in weight (blue duiker size) because a relatively large body size allows them to take in and store the large quantity of food necessary for their bodies to function. The upper size limit for ruminants is 1000 kg (2200 lb.) (giraffe size). Beyond this, there is not enough food available to maintain a bigger body.

Ruminants can partially recycle urea whereas non-ruminants cannot. This is why some ruminants, such as the camel and the oryx, are able to live in true desert conditions and zebras cannot. (Author’s note: Camels are frequently seen in East Africa but they are domesticated animals. This book does not deal with domesticated animals.)

Ruminants appear to be better able to subdivide habitat usage than non-ruminants. This is why there are more species of ruminants. In the Serengeti-Mara ecosystem, the ruminants include wildebeest, topi, kongoni, eland, Cape buffalo, klipspringer, bohor reedbuck, impala, Thomson’s gazelle, Grant’s gazelle, Masai giraffe, Kirk’s dikdik and common duiker. The hindgut fermenters (non-ruminants) are far fewer in species and in populations. They include the common zebra, three species of hyrax, hippopotamus, black rhinoceros and the African elephant.

Behavior Associated with Rumination

All ruminants have similar habits. They include:

• Lying down by kneeling first and then lowering rear
• Standing by doing the reverse
• Lying on their brisket or standing while chewing cud
• Ruminants rarely lie on their sides and almost never roll on their back
• If they were to lie on their sides for a long period they would ingest rumen contents and suffocate.
• Dozing often but not sleeping soundly as hindgut fermenters do
• Resource Partitioning

The Serengeti is able to support a wide variety of ruminants and hindgut fermenters because each species have evolved different feeding habits.

Antelope Behavior Guide

Self Advertising

• Animal stands or lies in a conspicuous location or posture
• Usually alone and away from herd
• Territorial or dominant males
• Often associated with this are noises such as grunts, roaring or snorting

Scent Marking:

• Defecating in one spot to create a midden or mound of dung; most territorial antelopes perform this (Dikdik, bushbuck)
• Scent marking using the preorbital gland to leave a scent on a twig or blade of grass
• Some species will also scent mark others of their kind
• Object horning; thrashing the vegetation to show aggression; often this is directed at a rival.

Self-Adornment:

• Coating horns, face and shoulders with mud (topi, wildebeest, eland)
• Carrying vegetation around on the head (Grant's gazelle, wildebeest)
• 
  

Dominance displays:

Dominance displays are non-aggressive ways of indicating an animals status. They may be performed by either males or females.

• Erect posture: the animal holds its head higher than normal; resembles alert stance
• Animal stands broadside to an opponent; this shows of the mass of its body and its horns
• Animals face each other and stare at each other (rarely seen)
• Walking towards another animal and causing it to move away; Supplanting is usually signaled by a stiff, formal approach

Offensive Threat Displays

These displays convey that the displayer is willing to fight.

Medial-Horn Threat:

• Neck is held almost even with the back; the head is down so that the horns point

Kneeling Position:

• Performed by species that fight on their knees (wildebeest, kongoni and topi)

Low-horn Threat

• The head is lowered so that the horns are pointed at the opponent

High-horn Threat:

• Neck is raised but nose is angled towards ground

Angle-horn Threat:

• Horns are displayed while the animals stand parallel to each other

Staring: 

• Animals look at each other for a period of time

Chasing:

• Aggressor will chase off a rival; common among adults chasing off young males

Cavorting: 

• Jumping, twisting and other such antics designed to show off the health of the performer

Submissive Behaviors

Submissive behavior is seen when an animal wishes to avoid a confrontation or fight. These behaviors include:

• Head low, chin out posture

Lying-out:

• Resembles the hiding behavior of a young calf. This is often a way of escaping unwanted attention (i.e. usually sexual in nature). It is most often practiced by bush-dwelling species of antelope.

Kneeling:

• The animal kneels as if it is about to lie down.

Avoidance

• Animal simply avoids close contact with aggressor.

Displacement Behaviors

These are behaviors which are identical to normal behaviors but are performed in such a way as to reduce conflict and stress.

Displacement Grazing: 

• An animal will suddenly become busy with grazing in the middle of an aggressive interaction.

Displacement Grooming:

• An animal will begin to groom another when it wishes to relieve tension.

Displacement Alarm:

• An animal will suddenly snort a warning when it wishes to relieve tension. These are usually ignored by other members of the herd. Somehow they sense that it is not a real warning.

Social Behavior

Antelope will engage in a number of activities that function to maintain the social groupings. These include: sniffing each other's noses and social grooming where two animals will take turns nibbling each other's coats. Sometimes they will mark each other using their preorbital scent glands.

Courtship Behavior

During the breeding (or rutting) season, courtship behavior is often viewed. Below are some of the more commonly seen behaviors.

Males:

• Low stretch: Male approaches female with neck stretched out and head low; also used when herding females
• Flehem: Although both sexes will perform this, the male is more often observed. The animal smells and licks the female's urine. It is analyzed by a special organ in the roof of the mouth called the Jacobson's Organ. The visual signs include: curled upper lip, head held high and slowly turned from side to side. The animal usually stands still.
• Pursuit: Male follows female around
• Foreleg Lift: Male will appear to be kicking the female by lifting a foreleg and hitting her in the trunk of her body. Males will also do this to other males they dominate.

Females:

• Unusually playful or skittish behavior advertises estrus
• Stands for mounting when she is ready to mate

Response to Predators

• Alert Posture: Animal stares at the approaching or suspected predator's location. Often the entire herd will face the danger before deciding what to do. All antelope do this and it can provide a handy tool for safarists to locate predators.

• Stamping: An antelope, having spotted something suspicious, stamps its foot. All antelope do this too.

• Stotting/ Pronking: A stylized jump where the antelope jumps off the ground using all four legs at once. This is a very costly display to make since it demands more energy than flat out running. Scientists believe that its purpose is to advertise how fit the animal is. "Don't waste your time chasing me", might well be the message. Performed by topi and Thomson's gazelles.

• High Jumping: Impala and eland will both perform this when escaping a predator. The high jumps serve to confuse the predator and to advertise the health of the animal. They also serve to alert other animals of the danger.

• Lying-out: Some species, when confronted with an enemy, will lie-out in the same position that very young animals might do. The species which do this are those that live in cover.

• Standing in cover: Large antelopes that live in bush and heavily covered areas will stand still and try to blend in with the cover.

• Skulking: Some antelope species that live in heavy cover will try to sneak away unseen.

• Freezing: Some species will run away and then suddenly freeze, hoping the predator will lose them in the bush cover.

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Dave Taylor's African Safari - Book 3: Trophic Level II - The Herbivores (Standard Version)
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