Take A Little Time
The ratio of males to females; the ratio of adults to immature animals; the ratio of young-of-the-year to breeding females and condition of the animals. Survival and predation may also be indicated. One must know what is 'normal' before being able to identify the 'abnormal' factors within a group or population.
Age AssessmentThe most commonly used feature for ageing wild animals 'in the field' is size related to adults. Colour is also significant in many species. Ageing criteria have been calculated for most species using tooth development and replacement recorded from known-age animals. For field use this has been related to shoulder height.
Where applicable, horn growth has also been used. The information is published in various journals and papers for interested managers and field workers. Accurate criteria for each species are too numerous to include in a short article but an attempt will be made to reproduce some of the more common ones in future. In the past, I have mentioned skull identification using tooth formulae. Most ungulates have three pre-molars and three molars on each quarter of the jaw - that is six teeth on the left and right upper and lower parts of the jaw. The pre-molars erupt in sequence from the front, first, followed by the molars in similar fashion, after which the pre-molars are replaced in sequence. This leaves PM 3 as the youngest tooth and M1 as the oldest tooth in the mouth of an adult animal. Most wear will be noted on M1. An animal with a full set of six teeth per quarter can be presumed to be full adult body size - and this can be applied to the length of skull. In the field, head size, combined with shoulder height, colour and behaviour are best indicators of age. Useful observations in assessing herd structure and recruitment are the ratio of calves, yearlings and subadults to breeding females. Adult females normally start breeding between two and a half to four and a half years old, depending on the species.
Male Or Female?In mammals, males are generally larger than females to enable them to compete for and dominate territories. There are a few exceptions, as in hyenas and some other species. Their structure enables them to withstand intra-specific competition and effect some physical control within a group. Males are generally more strikingly marked than females. (Note - that in birds of prey the female is larger than the male - probably for nestling protection, shading of chicks and ability to take larger prey during the breeding season. The lighter male is generally faster for year round hunting.)In certain ungulates only the males have horns, which makes for easy identification. In species where both sexes are horned, the males inevitably have heavier, although sometimes shorter, horns than the females. On young animals the base of the horn will be noticeably thicker in males. This criteria also applies to giraffe. In sable, roan and some other species of antelope the adult males have more curved horns than the females. In adult elephants the males normally have a more domed forehead and thicker, more curved tusks than females. Hippo bulls have a thicker neck. Adult buffalo bulls develop a heavy 'boss' between the horns. Giraffe bulls develop a bony growth on the forehead giving them a 'roman nose' while females tend to be 'dish faced'. Warthog males have thicker tusks and more prominent 'warts' on the side of the face. Zebra stallions have thicker necks than mares.
The various differences between males and females are described in numerous publications. The different genitalia of each sex are not always obvious in many species. The scrotum is usually visible and the penis can normally be noted when looking at the stomach line when not hidden by long grass. Apart from physical features there are behavioural aspects that assist in identifying different sexes.Males often tend to be solitary while females normally remain within a, sometimes closely scattered, group. Two animals 'sparring' will inevitably be males. Immature males of many species will often gather in bachelor groups and old, displaced males will frequently band together for protection.
ConditionAnimals in seriously poor condition are normally obvious. Thin, emaciated, lethargic and weak looking with ribs and hip bones showing, while erect, stark and lifeless hair may hide some signs of poverty. The hide of zebra, with a subcutaneous layer of cartilage, will not sag to show ribs and may give a false impression of their real condition. This applies to other thick skinned mammals where protruding hip bones and 'hollow' temples will be better indicators.
Zebra have a substantial layer of cartilaginous fat under the mane and when it good condition this holds the mane erect. When in poor condition the fat is depleted and the mane will sag or flop to one side. During the dry season, when animals congregate more closely, as at water points, sarcoptic mange may spread and be noticeable on certain animals. When this affliction becomes severe it will cause the animal to lose condition - and often results in death - but the infection is not caused by poor condition. Open wounds, scarring and limping due to various causes, are pretty obvious to any observer. Animals with impaired mobility become easier prey while injured carnivores will be less efficient and more prone to starvation. Lion cubs, after weaning and being at the bottom of the feeding 'peck order', are the most likely members of a pride to starve when food is scarce. It is more important that breeding adults survive.
Herd Structure And BehaviourCertain species are habitually nomadic (if not confined by fences) and range over the best feeding areas within reach of water supplies. Buffalo and eland are typical examples. Old males often go off on their own but generally the herds stay together and males strive for dominance and breeding opportunities within the herd.
In truly wild areas, herds will aggregate in large numbers during the dry season, providing an opportunity for gene transfer. In these aggregations they, and certain other species, become a natural mowing machine. Unable to stay long in one area they move through the un-grazed areas breaking the soil surface, trampling down uneaten vegetation and leaving behind quantities of 'fertiliser'.Having thus prepared the ground for new growth, they will again split into smaller herds at the onset of the rains. Paired species, such as steenbok, duiker and bushbuck, tend to be more territorial than herd species. Although not always together, they defend areas containing sufficient requirements. Their young are banished when mature and deaths are replaced by wandering, single adults. Being delicate feeders they do little damage to their habitat.
Kudu females tend to remain in their 'home area'. The adult males are nomadic and wander between best feeding grounds, joining the female herds during breeding season - around April, after the rains. In contrast, wildebeest females wander to best feeding grounds, while the males hold the 'home areas'. The dominant males will herd the females within the 'home areas' during breeding season. In a typical scenario - a herd would consist of a larger ratio of adult females to adult males. Under normal circumstances mating would be restricted to the dominant males. Rejected males would form small male groups - an indication of excess numbers. After breeding, the young (normally produced at a ratio of 50:50) would be tolerated within the herd until the next breeding season. When young males mature and become interested competitors for breeding, they are banished by the dominant males into bachelor herds (boarding schools).
Within these nomadic groups, the young males pioneer new areas and compete for dominance. Successful males will set up 'home areas' into which females can expand, or else they may challenge old males for existing female herds. Through interherd exchange and inter-male competition the gene pool is diversified and strengthened.
InterpretationToo many adult males to adult females is an indication of excess animals normally due to fence confinement. This will result in wasteful competition and reduce herd vigour. A low percentage of young to adult females indicates poor breeding or predation on young. Low yearling survival indicates predation (lack of cover or inability to escape due to confinement) or lack of food for weaners due to adult competition.
Physical condition, herd structure, birth and survival, in conjunction with trends in veld condition are some aspects to note when considering management options. The behaviour and population dynamics of various species provide fascinating hypotheses for the interested observer.