Science

Spoor Interpretation

Apart from identifying animal tracks and being able to follow a trail, trackers must also be able to interpret the animal's activities so that they can anticipate and predict its movements.

Lying, sitting and standing

The imprints made by an animal's body and by its legs folded underneath the body will indicate when an animal has been lying down. Where an animal has been lying down in grass, the grass will be flattened out in the shape of its body. The sitting position is usually revealed by the hind-limbs showing right up to the heels, with the imprints of the fore-feet in between and the tail showing behind. When standing, the feet are usually apart and pointing slightly outwards, especially the fore-feet.

Gaits

When footprints are neat and clear, showing all the fine detail that could possibly show, they usually indicate that the animal was standing stationary or moving slowly. When the animal was moving fast, the toes will have splayed, the feet may have slipped, sand may be kicked up and the footprint may be partly obliterated. The direction of movement and the length of the stride may be revealed by the depth and angle of the imprint, together with the direction in which the sand had been thrown. The length of the stride indicates the speed of the animal, while the positions of the tracks relative to each other reflect the animal's gait.

Page22Fig

Relative position of footprints for different gaits. The fore-foot tracks are indicated by black dots and the hind-foot tracks by white dots. Where the hind-foot track registers on the fore-foot track it is indicated by a half-black and half-white dot. Key: (a) slow walk (b) normal walk (c) trot (d) fast trot (e) trot with obliquely positioned footprints (e.g. foxes, jackals and some dogs) (f) transverse gallop (g) lateral gallop (h) transverse jump or bound (i) lateral jump or bound (j) half bound (k) jump with hind-feet tracks side by side (l) jump with hind-feet tracks registered in fore-feet tracks (m) stotting (n) bipedal hops. (After Bang and Dahlstrom, 1972)

Walking

When walking, each of the four feet is lifted and set down on the ground at a different time, each limb moving separately. The legs are moved in a definite order. The right fore-leg is followed by the left hind-leg, which is followed by the left fore-leg, which is followed by the right hind-leg, and so on. The hind-foot is always placed close to the point where the fore-foot was placed, so that its track is made a little behind, right over or just in front of the track of the fore-foot, depending on the speed the animal is walking. Where the fore-foot track is covered by that of the hind-foot, the tracks are said to register.

When the animal is walking slowly, the hind-foot track will be behind the fore-foot track, and when it is walking fast the hind-foot track will be in front of the fore-foot track. In the slow walk, only one foot is moved at a time, with three feet always on the ground. This is the normal walk of heavy animals such as Buffalo and rhinoceroses, while antelope move in this way while grazing.

In the normal and fast walk of most animals, two feet are in motion at the same time, each foot being followed by the next one when it is half way through its stride, and two feet are always on the ground.

In the running walk, the tempo is so fast that in some phases only a single foot is on the ground at a time. The running walk is not so speedy as the trot and few animals adopt it naturally, except the Elephant, whose only speedy gait this is.

Pacing

When pacing, the fore-leg and hind-leg of the same side move at the same time. At a walking speed, this gait is used by antelope like Springbok and Blesbok.

Trotting

When trotting, the diagonal feet are placed in pairs at the same time. For example, the right fore-foot and left hind-foot are lifted and set down at the same time, and then the left fore-foot and right hind-foot. With the slow trot, two feet are always on the ground; this is used by sluggish or clumsy animals such as tortoises and badgers. With the fast trot there is an interval of suspension, with no feet on the ground.

The trail is very similar to that produced by walking, but the stride is greater and the straddle less. The length of the stride is the distance between two successive tracks from the same foot, and the straddle is the distance, perpendicular to the direction of motion, between the left and right tracks. The faster an animal trots the greater is the stride and the smaller is the straddle, so that in a very fast trot the tracks of the right and left side almost lie on a single line. On firm ground the hind-foot usually strikes the ground in front of the track made by the fore-foot, and the faster the speed, the further in front it falls.

Some animals, like foxes, jackals and some dogs, leave a trotting trail in which both fore-foot tracks lie on one side and both hind-foot tracks on the other side. The trail appears as a row of obliquely positioned pairs of footprints, each of which consists of a fore-foot track with a hind-foot track placed obliquely forwards and to one side. This happens because the animal trots with its body positioned at an angle to the direction of travel so that the fore-legs are never in the way of the hind-legs. Now and again it may shift the rear part of its body to the other side.

Galloping

In the gallop there is a phase in which the animal is airborne. The four legs work in quick succession one after the other. The footfall sequence varies with the speed or kind of animal. In the transverse gallop, either one of the hind-feet is followed by the other and then by the diagonal fore-foot, followed by the other fore-foot. In the lateral gallop, either one of the hind-feet is followed by the other and then by the fore-foot on the same side, followed by the other fore-foot. An animal may lead with either front foot, or it may change from one to the other.

Page24Fig1

Walking: 1 The right hind-foot is placed in the track of the right fore-foot, which has just left the ground; when the right fore-foot is half-way through its stride, the left hind-foot leaves the ground, while the other two feet are on the ground. 2 The right fore-foot is placed on the ground, while the left hind-foot is half-way through its stride. 3 The left fore-foot leaves the ground just before the left hind-foot is placed in its tracks, while the animal is supported on the other two legs. 4 The left hind-foot is placed on the ground while the left fore-foot is moved forwards. 5 The right fore-foot is lifted, while the left hind-foot and right fore-foot are on the ground. The position as in No. 1, but with the opposite feet. The left fore-foot will be placed on the ground, followed by the right hind-foot, and so on. (After Bang and Dahlstrom, 1972)

Page25Fig1

Trotting: 1 With the left fore-foot and right hind-foot already off the ground, the animal takes off from the right fore-foot and left hind-foot. 2 While the animal is in the air, the left fore-foot and the right hind-leg are moved forwards. 3 The left fore-foot and the right hind-foot are placed on the ground simultaneously. The right hind-foot registers approximately in the track of the right fore-foot. 4 The animal is again in the air while the right fore-leg and left hind-leg now move forwards. 5 The right fore-foot and the left hind-foot are placed on the ground. The left hind-foot registers approximately in the track of the left fore-foot. (After Band and Dahlstrom, 1972)

Page25Fig2

Galloping: 1 The animal is supported on the fore-legs, but is shifting its weight from the left fore-leg to its right. The hind-legs are moving forwards. 2 In the take-off the weight of the animal is supported only on the right fore-foot. 3 The animal is in the air while the hind-legs move forwards. 4 The left hind-foot touches the ground, while the other legs move forwards. 5 The animal is supported on the right hind-leg and left fore-leg, but as the right fore-foot is placed on the ground, the hind-legs will move forwards as in No.1 . (After Bang and Dalhstrom, 1972)

Page25Fig2

Jumping: 1 The animal pushes off from the hind legs. 2 The animal is in the air with the fore-legs stretched out before landing. 3 The right fore-foot reaches the ground a fraction before the left fore-foot, after which the fore-feet leave the ground again. 4 The animal is in the air with all four legs tucked up under it. 5 The hind-legs reach the ground and start a new jump. (After Bang and Dahlstrom, 1972)

Bounding

As the speed of the gallop increases, the gait becomes more like a jump. The bound is a fast gait intermediate between a gallop and a jump, in which the take-off of the hind-limb lifts it from the ground and propels it into the air. Mammals with short legs or long, limper bodies use the hind-legs close together or even employ them as a unit to accomplish the half-bound or the bound, but the fore-feet are used separately. There are many possible transitions between a jump and a gallop so that it is not possible to define any sharp boundary between them.

Jumping or hopping

In jumping or hopping, the animal is momentarily airborne, taking off with both hind-legs so that it is projected forwards in an arc, and landing on the fore-legs, which usually hit the ground one a little in front of the other. The fore-legs carry the animal a short distance forwards, and then leave the ground again. The hind-legs then land a little in front of the fore-foot tracks.

A jumping trail consists of groups of four footprints. The two fore-foot tracks will lie close to each other, with one a little behind the other, and in front of them the hind-foot tracks will lie more or less side by side. In some animals one or both of the hind-feet may register with the tracks of the fore-feet. Jumping or hopping is the commonest gait of many small animals with powerful hind-legs, such as small rodents.

Stotting

Stotting is performed by animals such as Springbok and Oribi when they are under stress or being chased. The back is arched and the legs are held stiffly downwards as the animal leaps off the ground. It lands on all four legs simultaneously and then shoots up into the air again, repeating the movement several times.

Bipedal hop

In the bipedal hop, both hind-feet are used in unison, while the fore-feet are held close to the body. A long tail usually provides balance. This gait is used by mammals with powerful hind-legs and reduced fore-legs, such as the Springhare and the Bushbaby. In the trail, the tracks occur in pairs.

Bipedal walk and run

Bipedal walking, in which the hind-legs are used alternately, produces tracks in a zigzag or sometimes in a straight line. In running, the length of the stride is greater than in walking, but the straddle is less.

Actions

Apart from specific gaits, the various actions of the animal may also be indicated by the tracks.

Signs of digging may be characteristic of the species, such as the distinctive claw-marks made by the Springhare and the Antbear, or the narrow hole dug by the Bat-eared Fox. The type of food dug out, whether roots, bulbs or termites, may also indicate the animal involved. Animals like Baboons turn over rocks to look for insects, spiders or scorpions, and pull up clumps of grass and shake off the soil before eating them.

Feeding signs of specific animals will not only indicate what they were feeding on, but also how they were feeding. The methods of handling food may be characteristic of a species.

Grooming activities will be indicated by the position in which the animal was sitting to scratch itself. Signs of rolling on the ground may be evident where an animal had a dust bath or wallowed in mud. Animals like rhinoceroses rub themselves against logs, which often become well worn after repeated use.

Territorial male antelopes may demonstrate the presence of a threat by pawing and horning of shrubbery. Ground-horning in moist, soft ground may also be carried out by some antelope.

Virtually all conceivable actions leave distinctive markings, which may make it possible for the tracker to reconstruct the animal's activities.

Determining the age of spoor

One of the most difficult aspects of spoor interpretation is determining the age of spoor. Only a very experienced tracker can fix the age with reasonable accuracy, while absolute accuracy is probably impossible.

A reasonably accurate way of determining the age of spoor is possible if an animal was resting in the shade of a bush. The position of the marks on the ground where the animal was lying or standing indicates where the shade fell, and therefore what the position of the sun was, so it is possible to calculate from the movement of the sun when the animal rested.

If the tracks of a moving animal go under the west side of trees, the animal was catching the morning shade, while if they go under the east side, the afternoon shade, and if under either side, the animal was moving at midday.

When studying the ageing processes of spoor, a tracker can only make an intuitive estimate of the age. In some cases, where the ageing process is relatively rapid, it is possible to make a reasonably accurate estimate. However, because of the complexity of factors involved, accuracy is usually not possible, especially where the ageing processes are slow and variable.

Heat and humidity, which determine the rate at which moisture content is lost, may vary considerably depending on the time of the day, the prevailing weather conditions and the season. Spoor ages faster in the heat of the day than during the cooler part of the day or night. On a hot, dry day it will age faster than on a cool, humid day, so the rate of ageing may vary considerably from one season to another. Wind not only increases the rate at which moisture is lost, but also has an eroding effect. Tracks made in shade and shelter will also be less affected by the sun and wind.

The most accurate indications of spoor age are provided by signs that involve rapid moisture loss, since these signs change relatively rapidly in the early stages. Examples of such signs are saliva on the leaves or on the ground where the animal was feeding or licking for salt, fresh urine and droppings, and water that has been splashed on the ground next to waterholes or rivers.

In muddy ground, tracks may dry out in a very short time or may remain wet for a long time, depending on the moisture content of the ground and the weather conditions. Wet ground can be very misleading as any spoor remains visible and fresh-looking for a considerable time. Once dried out, footprints may retain their fresh, sharp appearance for a very long time, so it will be very difficult to make an accurate estimate of their age.

The rate at which the wind erodes a spoor is usually hard to estimate, because it may vary considerably depending on how strong and for how long the wind was blowing. Fresh footprints will have sharp edges which will be rounded off by the wind. Over time they will lose definition, and leaves, seeds and loose sand will gather in them. Leaf spoor, created by leaves rolling in the wind, may also be superimposed on the tracks.

The rate of discolouring of spoor is also difficult to estimate, since changes may be very subtle and the rate of change may be very slow. Fresh footprints expose the darker colour of the ground beneath the surface, which will gradually change to the colour of the ground on top as it is exposed to the sun. When stones and leaves are overturned, their darker undersides become exposed, and these will also gradually become lighter in colour.

Broken vegetation will discolour at the break, and the rate of change may differ for various types of vegetation as well as according to the prevailing weather conditions. To obtain an indication of the colour change, a new break should be made and compared with the old. Leaves may also be knocked down by a moving animal, or dropped by a feeding animal. These leaves are sometimes still green when they drop on the ground and will discolour as they dry out. Furthermore, one can sometimes determine when a flattened tuft of grass was stepped on by noting the amount of spring-back.

The activities of an animal may help provide an approximate estimate of the age of spoor if its habits are known. If an animal is either diurnal or nocturnal, the tracks would have been made either in the day or in the night. During the midday heat, an animal may rest up in a dense thicket, or at night it may sleep out in the open. Some animals go to waterholes or pans at specific times of the day, and move to their favoured ground according to a set routine.

On the basis of a detailed knowledge of the habits and movements of other animals, one can determine the relative age of a spoor from superimposed animal spoor. If the spoor of a nocturnal animal is superimposed on the quarry's spoor, the latter was probably made during the night or the previous day. Furthermore, if the quarry is diurnal, then its spoor would have been made the previous day. If the quarry's spoor is superimposed on a nocturnal animal's spoor, the former was probably made during the night or earlier that same day, and if the quarry is diurnal, it would have been made the same day. In the process of tracking the quarry, the spoor of several animals may be found superimposed on top of the quarry's spoor, or the quarry's spoor superimposed on the spoor of other animals, so that an upper and lower limit for the age of the quarry's, spoor can be determined.

Dew, mist and rain may also give an indication of the relative age of spoor. If dew has fallen on top of the spoor, the spoor was made during the night or the previous day, while spoor on top of dew would have been made earlier that same day. Dew dripping from branches may also form pock marks in spoor made during the night or early morning. Spoor through long grass, made before dew or rain, will be covered with drops. If it was made after dew or rain, the drops will be shed off. Again, if rain or mist has fallen since the track was made, there will be pock marks in the track. Conversely, if a track was made after rain or mist has fallen, there will be pock marks around but not inside it. Heavy ground fog will also smooth down spoor and leave pock marks under leafy branches.

Although superimposed animal spoor, dew, mist or rain do not enable one to determine the actual age of the spoor, they do indicate the chronological sequence of a series of events involving the animal. As more information is gathered, the tracker may revise his or her hypotheses to recreate a more detailed sequence of events, combining information on the animal's own activities with an understanding of when these occurred relative to other animals' activities.

Reconstruction of activities

To reconstruct an animal's activities, specific actions and movements must be seen in the context of the animal's whole environment at specific times and places.

Where an animal is moving at a steady pace in a specific direction, or following the easiest route along a well-defined path, and it is known that there is a waterhole ahead, one can predict that the animal is probably going to the waterhole. A browsing antelope will move slowly from bush to bush, usually in an upwind direction, so a tracker who knows its favourite food will he able to anticipate the next bush the antelope would have gone to.

The animal's relationships with other animals also influence its actions and reactions. If a walking or trotting animal stops to look at something, this will be indicated by the fore-feet being turned towards the direction the animal was looking. There may be signs of a confrontation between a territorial male antelope and an intruder, such as pawing marks and horning of shrubbery by the one, and signs of flight by the other, or signs of fighting between two serious competitors. Signs of a sudden stampede often indicate that the animals were fleeing from danger, and the tracks of a predator may be found close by. Or tracks will show where a predator stalked its prey, and rushed up to bring down the fleeing animal. The fleeing animal may have been crashing through bushes, and its skeletal remains are sometimes surrounded by signs of its last struggle, followed by signs of feeding predators with the spoor of scavengers superimposed on those of the predators.

Since tracks may be partly obliterated or difficult to see, trackers will only have fractional evidence, and their reconstruction of the animal's activities will have to be based on creative hypotheses. To interpret the spoor they must use their imagination to visualise what the animal would have been doing to create such markings. Such a reconstruction will contain more information than is evident from the spoor, and would therefore be partly factual and partly hypothetical. As new factual information is gathered in the process of tracking, hypotheses may have to be revised or replaced by better ones.

Detailed knowledge of an animal's habits, which may partly be based on hypothetical spoor interpretation, as well as knowledge of the environment, enables the tracker to extrapolate from incomplete evidence to recreate a complete account of the animal's activities. Spoor interpretation need not only be derived from evidence from the spoor itself, but also from activities implied by the spoor in the context of the environment and in the light of the tracker's knowledge of the animal's behaviour. A hypothetical reconstruction of the animal's activities usually enables the tracker to anticipate and predict the animal's movements.