Last update: November 24, 2010 11:26:36 AM E-mail Print

 

Impala “Rooibok”

Aepyceros melampus  (Lichtenstein, 1812)

 

Deon Furstenburg

ARC-Range & Forage Institute

Grootfontein

 


Impala surely has become the most abundant of all game species on private land.  For many a game farmer and rancher impala has become the survival aid of his game business.  It is also the most important prey animal to larger predators, often being managed for this exact reason –  acting as a buffer in preventing more valuable species from falling to prey.  Impala has always being important in keeping the venison pot cooking in the kitchen and the biltong tray stagged.  In the south western regions its place is taken by the springbok filling a similar production niche.  The name impala comes from the Zulu name iMpala.  In Tswana it is called phala.  It was first described by the German zoologist Lichtenstein, who saw the animal in 1805 some 50 km south west of Kuruman at Khosis.  This site record later came to be the most south-western distribution ever being documented.  The water courses to the north-east of Kuruman seem to have been well inhabited by impala up to the early 1900's.

 

The basic body form of the present impala remained almost unchanged through historic times.  There has never been more than one species of impala at any given time.  Such evolutionary stability is astounding considering that the close related alcelaphine antelopes (blesbok, hartebeest and wildebeest) who shared a common ancestor with the impala, split into new species at least 18 times.  Impala managed to survive and increase throughout the settlement of past and modern human development.  This delicate fast and graceful animal succeeded in its co-existence due to its ability to alternate between grass and dicot (browse) feeding and thus, its dispersal into ecotone habitats between grasslands and woodlands.   Such ecotones have increased with the spread of man and his related farming practices due to overgrazing by livestock and fertilization of pastures on the banks of drainage lines.  

 

Taxonomy & Distribution

Seven subspecies are being recognised: 1) the Southern Impala - including Aepyceros melampus melampus, A. m. johnstoni, A. m. katangae, A. m. holubi; 2) the East African Impala - including A. m. suara, A. m. rendilis; and 3) the Black-faced Impala A. m. petersi.  Impala are endemic to the African continent and only the black-faced and southern impala occur within the southern subregion south of the Zambezi river.  The southern impala is naturally distributed through the eastern regions of central and southern Africa including Kenya, Uganda, Tanzania, Zaire, Zambia, Angola, Botswana, Zimbabwe, Mozambique and the Lowveld, Bushveld and Kalahari regions of South Africa.  Black-faced impala are restricted to the south western regions of Angola, north western regions of Namibia and scattered pockets along the western Zambezi river.  In South Africa impala are found in the bushveld and savanna areas to the north of the N14 national route between Kuruman and Pretoria, north of the N4 between Pretoria and Komatipoort and east of the Drakensberg.  Although impala did not formerly occur in the eastern Cape bushveld they had been successfully introduced across the entire area, as far south as Uitenhage.  They had also been introduced into the Orange Free State and the eastern Karoo.  At present they are to be found in 8 of the 9 provinces of South Africa.

 

Animal Characteristics

Adult impala rams weigh 48-65 kg (avg 57), are 22% heavier than the ewes (38-52 kg; avg 41) and 9% larger (shoulder height 85-95 cm) than the ewes (80-88 cm).  The skin is shiny with short hair (10 mm) which lies flat against the body.  Skin colour is a uniform chestnut brown on the back and around the neck passing through light fawn on the flanks and outer legs to white on the belly and the inside of the legs.  The colour darkens on the forehead and back-saddle of mature territorial males.  Distinctive is the oval tufts of blackish hair “socks” on the hind feet above the hoofs covering glandular areas secreting a cheese-like scenting substance.  Also distinctive is the black stripe down the back of each buttocks and the tail.  Black-faced impala is similar in size (rams 63 kg and ewes 50 kg; shoulder height 88 cm).  It differs from other impala in that it is darker coloured, a dull purple brown, with a distinctive purplish-black blaze down the middle of the face.  East African impala is of a brighter tawny hue and is more sharply edged along the flanks.  Ewes has 4 teats and the spoor is typical split-hoofed (5,5 cm long and 4,0 cm wide) and sharp tapered towards the front.  Only the males carries horns, although deformed under developed horns are not uncommon with ewes.

 

Trophy

Horns are lyrate shaped, in excess of 50 cm length and course ringed on the front surfaces for 75% of the length.  The tips are smooth and the number of rings relate to age.  Black-faced impala has smaller horns and the eastern African impala bares longer and thicker horns with a much wider tip-to-tip spread than the southern impala.

 

 

Southern impala Information Table

Characteristic                      Ram                           Ewe

Adult body mass                     48-65 kg, Avg 57 kg           38-52 kg, Avg 41 kg

Adult shoulder height               85-95 cm                      80-88 cm

Sexual maturity                     16 months                     13 months

Social maturity (first mating)      3 years                       18 months

Gestation period                                                  6,5 months

First lamb born                                                   23 months             

Lambing interval                                                  12-16 months

Fecundity                                                         97%

Last mating                         7-9 years                     10-11 years

Mating (Rutting) season (SA)                      April - June

Lambing season   (SA)                                             Oct-Dec

        (Zimbabwe, Nov-Jan), (East Africa, Year round), (Black-faced, Dec-Jan)

Weaning age                                       3 months

Sex ratio of population (natural)   1               :             1,1

Sex ratio adults (natural mating)   1               :             3

Sex ratio adults (production)       1               :             5

Sex ratio population (production)   1               :             1,6

Sex ratio calves born               1               :             1

Annual population growth                          23-35% (mortality included)

Natural mean mortality (population) 26% (from birth)

Expected life span                  10-12 years                   10-12 years

Home range                          200-400 ha                    250-700 ha

Territory                           4-10 ha                       None

 

 

Rowland Ward Trophy Records

Minimum qualifying length:      East African impala =          263/8" (66,99cm)

                                Southern impala =              235/8" (60,00cm)

                                Black-faced impala =          207/8" (53,02cm)

Maximum:

East African impala -           361/8" (91,76cm), Kenya, 1937, Ct. G Ahlefeldt-Bille

Black-faced impala -            263/4" (67,95cm), Namibia 1991, Dr. B. Gunther

Southern impala -                

1)   317/8" (80,96cm), Limpopo, N,Tvl., 1946, J.V. Edgar-Jones

2)   31" (78,74cm), Potgietersrus, N.Tvl., 1938, J.V. Edgar-Jones

3)   291/4" (74,30cm), Thabazimbi, N.Tvl., 1992, Pat Ellis

4)   291/4" (74,30cm), Alldays, N.Tvl., 1997, D.M. de Fortier

5)   291/8" (73,98cm), Transvaal, 1967, P.J. Rautenbach   

                                               

 

Impala growth rate in relation to age

Age

Body mass (kg)

Horn

 

 

Length (cm)

Number of rings

Birth

4,5

0

0

8 weeks

7

0

0

4 moths

12

0,5-4

0

6 months

16

10-15

0

12 months

25-30

20-30

1

18 months

30-35

32-40

4-6

24 months

33-40

38-48

9-13

30 months

36-45

42-54

15-18

3 years

38-50

46-58

16-22

4 years

40-55

50-64

18-24

5 years

40-58

>52

20-24

6 years

40-64

>52

20-24

                                                                                                                                               

 

 

Habitat Requirements and Distribution

Throughout the distribution range impala is associated with bushveld, savanna and open woodland habitats mainly upon alluvial and volcanic clay soils and with an annual rainfall precipitation of 400 to 700 mm.  Habitats encompassing a diverse tree and shrub composition are favoured, especially if it includes various Acacia, Combretum, Terminalia, Dichrostachys, Grewia and Mopane trees.  Rocky outcrops, mountain slopes, open grassland, marshlands, arid environments, riverine thickets and forests are mostly avoided.  Although impala inhabit habitats on sandy soils it is not preferred due to it generally comprising tall less palatable grasses.  Ecotones on the perimeter of riverine thickets and closed woodland are well sought for.  Habitat requirements vary in relation to seasonal changes.  Territorial males and female breeding groups generally occupies the better of any habitat, with bachelor male groups keeping to the more marginal areas.  Overgrazed areas result an increase of annual forbs in most woodland vegetation types.  Overgrazing thus improves veldconditions in favour of impala.  Black-faced impala in contrast prefer more dense habitats such as riverine thickets bordering open and closed woodland vegetation.   

 

Behaviour  

Impala are known to associate with other gregarious animal species such as blue wildebeest, zebra, baboon, waterbuck and giraffe.  Advantage is gained in sharing the guardiance and senses of the other species in detecting danger.  Safe distance kept from potential danger is generally 20-60 m. Predators are often allowed to close in to 30 m before impala will turn to flight.  They depend upon swift movement and enormous leaps (up to 2,5 m heigh and up to 12 m distance) in escaping.  Flight speed reaches up to 60 km/hr.  The group splits up with individuals making for all different direction.  Group members do not follow each other in flight as do many other antilope.  They will only regroup after considerable distance from the impact (150-400 m).  When danger prevails the subadult males in the group will position themselves between the danger and the females, with the young moving to the opposite side of the group.  Impala rely on scent rather than sight to detect danger. 

 

Impala is area bounded, therefore the same group are frequently found in the same vicinity.  Mean distance of 24 hour movement is 2,5-3 km.  Because they drink every second day from any of 1-3 water holes within the home range they can easily be awaited at the water.  During hotter day hours they become less active mostly keeping to shade.  They feed for 38% out of 24 hours of which less than 35% takes place during night hours.

 

Nutrition

Impala are mixed feeder ruminants being both a browser and a grazer.  The ratio of browse to grass taken in the diet varies with season depending upon rainfall and the habitat within which they roam.  They are highly selective towards both plant species and plant parts, thus being classified as a concentrate feeder (selecting only high quality fodder).  The most important parameter for fodder selection is the nutritive quality and palatability of the plant material to be utilized.  A low crude fibre (<40%) and high protein (8% in winter to16% in summer) diet is required.  During moist conditions the diet consists predominantly of short (<8 cm), sweet grasses (79-92% of diet), herbs and forbs and little browse.  As the lignin content of grass increase on entering dry conditions the diet changes to 32-67% woody browse.  The rumen and duct changes physiologically by increasing the thickness of the duct wall and enlarging the epithelium papillae from 6 to 11 mm (enlargement of the absorption surface) in relation to an increase in crude fibre content in winter and vice versa.  Also the acidity in the rumen increases from 6,7 PH to 5,8 PH and the protozoa composition enriches during winter months. 

 

Impala being a concentrate feeder is in contrast to the kudu (also a browser) that is a roughage “bulkish” feeder consuming a high fiber diet year round.  The success of impala to sustain itself in various different habitats is attributed to the above physio-morphological adaption of the duct.  Daily protein requirement for an adult female increases from 0,5 g/day (non-lactating) to 22 g/day at birth and decline again thereafter.  Daily food intake of adults ranges from 0,9 kg/day dried material in winter to 1,9 kg/day in summer.  Impala is strongly attracted to new growth of both grass and browse on recently burnt veld within close vicinity of the home range – take note that impala do not migrate and can not be lured over distances.

 

Impala as for kudu and giraffe is severely negatively affected by secondary metabolites such as tannin and glycosides.  Therefore they need to feed across a large diversity of fodder plants.  The author has studied impala in the mixed bushveld of the Waterberg (Naboomspruit) to include 65 plant species in the diet of a single herd.  Literature list up to 87 species to be taken by the southern impala.  Important species are – grass: Cynodon, Panicum, Digitaria, Eragrostis, Brachiaria, Pogonarthria, Melinis, Themeda, Urochloa – forbs: Asparagus, Cleome, Justicia, Sida, Tephrosia, Waltheria – browse: Acacia, Carissa, Combretum, Dichrostachys, Grewia, Mundulea, Terminalia, Ziziphus, Securinega, Capparis, Mopane as well as berries, fruit and fallen pods.  Fallen pods is a very important source of protein during dry winter months.

 

During the late summer months (January to March) the socially mature males increase their feeding behaviour as to build up body reserves of stored energy for the rut when time for feeding fades.  Energy reserves are stored as a protein deposit in a layer “brown”-fat called blubber, surrounding the neck muscles.  This can be seen from the physical thickening of the neck of mature males. 

 

Preferred browsing height is 40-100 cm, but the full range extends from ground level to 130 cm.  With overstocking of impala a distinct browse line develops at 130 cm, the herbaceous vegetation layer gets eradicated and the desired decreaser grass species get replaced by increaser species resulting in lesser ground cover.  Due to its selectiveness and its gregarious behaviour, impala is a high impact animal upon veldcondition and therefore need to be strictly managed.  Impala is well acceptive towards supplementary and artificial feeding and take both dried lucern and concentrate antilope cubes.  With mineral deficiencies they eagerly take both salt and concentrate licks.  Approximately 4 liter of water is taken every second day.  Therefore they tend to stick within 1,6 km from the nearest water.  Impala are not fond of drinking from artificial water troughs.  Drinking holes need to be designed to be level with ground surface.

 

Territory & Home Range

Home ranges varies from 200 to 700 ha depending on veldcondition and animal density.  Home ranges are stable and fixed year round.  Impala are not migratory and roams approximately 8,4 ha per day.  Socially mature males establish temporary territories of between 4 and 10 ha only during the rut, which they defend aggressively.  Several territories of different males falls within the home range of a female breeding herd.   Females are not territorial and will not take part in defense.  During wet seasons the herds split up in smaller groups (<20), but in the dry they are more concentrated and congregates in greater herds of up to 300 animals.

 

Social behaviour & Reproduction

Impala are social gregarious animals keeping in groups of 6-30 in summer, but aggregate in the winter.  Family herds consists of ewes of all ages, lambs, sub-adult rams and a few adult rams. Bachelor herds forms during the rut (January to April) consisting mainly of sexually mature, but socially immature rams.  Temporary nursing groups of youngsters form on the outer skirts of the family herds and are accompanied by one or two adult females.  Bachelor herds tend to stick to the perimeters of the home ranges of the family herds.  Rams reaches sexual maturity at 16 months and ewes at 13 months, but social maturity (age of first mating) is reached at 3 years for rams and 18 months for ewes.  Gestation period is 185-205 days and the lambing season differs with geographic area -- in South Africa it is from October to January.  90% of all lambs are born within a short period of 3-5 weeks.  This behaviour reduces mortality of the lambs to predators.   Lambs associate with their mothers only during suckling -- the rest of the time they keep to the nursing groups -- though family bonding is very poor.  Natural mating sex ratio is 1 socially mature ram : 3 socially mature ewes giving an annual population growth of 23-35% depending on environmental conditions and mortalities.   Natural live span is 8-12 years. 

 

From the end of January the dominant rams become aggressive as the rut approaches.  They utter vocalized roaring grunts and fierce full displays.  At the end of the rut they establish well defined territories.  Declining daylight hours stimulates increased hormone production enabling blubber build up in the neck. The enlarged appearance of the neck due to the blubber triggers estrous of the females.  Territorial males try to confine the moving female herds for as long as possible, generally for 8-12 days. Hereafter he becomes to weak and the females moves on, often the male then becomes displaced by another challenging male.  After 8 years the rams become post mature and leave both the family and bachelor herds to form their own little groups of 2-4 individuals (mostly trophy quality animals).

 

Production

Adult body size is reached at 2,5-3 years age and Rowland Ward trophy status only after 5 years.  Important is that the lambing percentage of 2-year ewes is 60%, wheras it is 97% for 3 to7-year olds and 70-80% for ewes >8 years.  Although the mean annual population growth ranges from 23-35%, it can reach up to 45% during favourable good rainfall years exceeding 650 mm. A 1 000 ha of optimal impala habitat at a rainfall of 400 mm can sustain a maximum of 300 impala, provided that no competition exists from other game species.  At 600 mm the same land may carry up to 600 impala, but this is not sustainable as great die-offs will appear when normal or less than normal rainfall occurs again.  Starting with 8 animals 300 will be reached only after 9-10 years, starting with 50 animals 300 can be reached after 5 years and 1 000 after 9 years.  Maximum mating ratio of the population are not to increase above 1% : 7& as then the breeding rate will deplete with ewes not being mated.   The most optimal ratio has been found to be 1 : 5.  An impala animal unit (AU) is 50 kg which equals 0,11 large stock units (LSU) and 0,38 browser units (BU) – a BU equals a non-lactating kudu of 120-140 kg feeding upon 1500 edible, palatable shrubs with canopy fodder <2 m height all year round (must retain at least 30% of its leaves).  Each impala AU thus, needs a minimum of 2-4 ha suitable grazing and 650 acceptable edible shrubs to survive.

 

South African impala live sale price dynamics

Average of all game sales:                         1976 - R82       1991 - R212

1995 - R365                    1996 - R475         1997 - R621      1998 - R577

1999 - R565                    2000 - R594         2001 - R640

 

 

 

Deon Furstenburg

Wildlife Scientist, Agricultural Research Council,

Middelburg, Eastern Cape,

email : Deon Furstenburg

(Available for professional consultancies)