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Impala herd structure/ calving

There are five types of impala herd structures or groupings.

  • Bachelor groups.

These are made up of impala rams of two years and older. During the rut, two year old males are evicted by dominant herd rams and join up to form bachelor groups from which dominant males will eventually emerge to establish their own territories when they are older. Bachelor herd formation peaks during the rut. After the rut bachelor members can and will often rejoin family groups.

  • Lone rams.

These are sexually mature animals who leave the bachelor groups to challenge for or establish their own territories. They will actively mark off boundaries using dung middens and urine deposits as well as advertising their territory by specific behavioural patterns. Standing tall and prominent, snorting, chasing competitors or trespassers and actively herding bypassing female groups in an effort to get them to stay within the territorial boundaries so that breeding can take place. Old rams that have passed their peak are often solitary. Solitary animals are very prone to predation.

  • Breeding herds (during the rut)

During the rut (April – May) the breeding herd consists of females of all ages and males younger than two years and a dominant breeding ram. The dominant ram will sometimes tolerate submissive males but generally evicts them or prefers them to keep their distance. Rams of two years or older will sometimes hang around on the periphery of breeding herds or will form bachelor groups.

  • Family groups.

Between ruts, adult rams are not strongly territorial so that at these times herds become mixed and one can find all ages of both sexes happily coexisting. Their appears to be a secondary but much less intense display of territorial behaviour during the lambing season (November – January). Some adult rams will show types of behaviour that are observed during the rut but it is half-hearted and they are not very serious or persistent and are very tolerant.

  • Nursery groups.

This cannot be defined as a herd structure per se but as a sub-group of family groups. Young lambs begin to aggregate and associate together and can often be seen grooming one another or cavorting and playing. They are usually presided over by a few adult females. Images above (top right) show a breeding herd consisting of a dominant territorial ram, his harem of adult ewes and animals younger than two years. The lower two images demonstrate nursery groups consisting of young lambs being tended to by a few adult females.

Impala with steenbok Impala and steenbok (Raphicerus campestris – Thunberg, 1811) can happily co-exist in the same habitat although the shy and nervous disposition of the steenbok results in it keeping much to itself. The rufous colouring of the steenbok is very similar to that of impala but there is no mistaking the two species. Even an impala lamb of similar size to an adult steenbok can be clearly differentiated by virtue of markings which will be discussed in more detail in due course. An adult steenbok weighs approximately 13 kg (30 pounds) and stands about 56cm ( 22 inches) at the shoulder. They prefer open plains with scattered bush. They live alone and are observed in pairs only during the breeding season. They have very short tails and males carry short, sharp horns. They are both grazers and browsers and appear to be relatively independent of water. The black patch on the nose and white underparts are very diagnostic. They are similar to and can be mistaken with the grysbok. Steenbok however prefer flat country as opposed to the grysbok’s preference for hilly terrain. When steenbok run off they hold their heads up high whereas grysbok keep their heads held low.

Distinctive markings of an impala Impala have very distinctive markings as shown in the above images. They have a white spot above the eyes which elongates forward into a stripe and a black spot high on the forehead. The tips of the ears are black and the insides of the ears and the muzzle are white. There are also two distinct stripes radiating from the base of the tail down along the thighs which stand out clearly against the pale brown background. The dorsal side of the tail is black which extends in a thin black line up the back. The ventral side of the tail is pure white.

Glands on back of feet Just above the fetlock of the hind legs are distinct oval patches of black hair which overlie a dense patch of glandular skin tissue. It produces a secretion which has a fairly pleasant smell but is of uncertain function. One suggestion has been put forward which claims that the gland is fluffed open during alarm leaps to leave an airborne scent trail for the rest of the herd to follow.