SOCIAL RELATIONSHIPS
Scent marking and agonistic behavior:
Courtesy of www.ultimateungulate.com
Urination and defecation, apart from being unavoidable physiological processes, have acquired important secondary functions in many ungulates, especially those with localized defecation (that tend to form dung heaps). Leuthold (1977), based on his own observations in Tsavo National Park and on the general observations of the species to date, suggests that gerenuks might be moving, evolutionarily, toward localized defecation. Although no true dung heaps were found by him, at least some old dung pellets were found at most sites where gerenuks recently relieved themselves. Furthermore, male gerenuks often perform a distinct, ritualized sequence of movements upon defecation, and they also usually urinate and defecate at the same spot, as opposed to the females. The male sniffs the ground, scrapes it with one or both of his forefeet, urinates, then defecates. This comes to show that the excretory processes have assumed a novel function, one with a social significance. For adult males this could imply territorial marking, with the animals relying both on the visual effect (conspicuous position of the body) and on the olfactory effect (Leuthold 1978).
A more striking feature of the species is the inclination of male gerenuks to scent-mark using secretion from their antorbital glands. The glands are situated in pits in front of the eyes. The scent is usually deposited in the following manner: the male approaches a twig, sniffs and sometimes licks it, then rubs his glands against it with slow, shaking motions of the head. These deliberate motions may have a visual display value themselves, particularly when the marking is done during an agonistic encounter (Leuthold 1977). Antorbital gland marks in the gerenuk are found mostly on conspicuous plants, on species that are normally eaten by the animal, and, as a pattern, form an irregular oval shape that sometimes branches out. Gosling (1981) suggests that the male has an advantage of marking a larger territory while conserving his supply of secretion and also his time.
Leuthold (1978) describes a brief fight between two adult males where both animals had their antorbital pits wide open, and the winner deposited his secretion in a demonstrative manner once the fight was over. Fighting is rare among gerenuks. Part of the reason may be that adult males have few incentives to infringe upon somebody else’s “property.” In contrast to the gerenuk, the males of certain other species are forced to transgress foreign territories during the dry season, in order to reach water sources (Owen-Smith 1977).
When an agonistic encounter does occur, the animals will first try to challenge each other without physical contact. The intimidation stage involves erection of the neck and body, sudden lowering of the head, looking away, or persistent head-shaking. Thrashing nearby branches with the horns may also occur, although the same behavior is observed when a male is alone. In the course of actual physical aggression, the two gerenuks violently swish their tales ( Leuthold 1978).
The gerenuk is one of the few species that mark the female’s hindquarters or shoulders with antorbital gland secretion, during courtship. This probably serves to establish a bond between the male and the female, even though that bond may exist only during the period of estrous (Leuthold 1977).
According to Leuthold, territoriality and olfactory marking are not necessarily correlated. This seems especially true in the case of glandular depositions, which are never found along an inhabited area’s boundaries. However, because of their important property of conveying information about an animal’s status, age, etc., scent markings do seem to play a role in social life and may elicit the “respect” of individuals that trespass an area inhabited by another male. Leuthold, nonetheless, also suggests that olfactory marking may serve to create a feeling of familiar surroundings, which may be important for the psychological comfort of the animal, including its behavior in social situations and aggressive encounters in particular. In mice, it turns out that the winner in a conflict is more often the one that is placed in a familiar olfactory setting. That could be the primary reason why captive animals set out to deposit their scent immediately after arriving in a new area (1977).
Courtship behavior:
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When a male gerenuk meets a female in estrous, his first reaction is triggered by pheromones emanating from the female. He advances toward her with his neck and head extended forward, sniffs her vulva and induces her to urinate. Then he adopts a posture common in almost all male ungulates – what Leuthold calls “Flehmen” or “lip-curl”: he curls his lips, turns his head slowly from side to side and often licks the liquid released by his potential mate. He essentially performs an “urinalysis,” which helps him assess the female’s reproductive status (Leuthold 1977). In the past, zoo keepers used to provide captive gerenuks with fresh drinking water (something these animals do not need in nature). This resulted in more diluted female urine and supposedly prevented successful breeding because males use urine signals to determine the sexual status of a female ("Research").
If the male determines that the female is conducive to mating, he performs a very pronounced “leg beat” ritual, where he gently thrusts his foreleg between the female’s hindlegs. By doing so, he assures his mate that he poses no threat to her and so reduces her flight response. Furthermore, the “leg beat” ritual allows him to test whether the female is ready to be mounted. The last piece of precopulatory behavior, the antorbital marking of the female, is characteristic of the males of only one other species – the dibatag (Leuthold 1977).
Mating system:
The mating system can be defined as overlap promiscuity. No long-term associations are formed between the male and the female. Even though females are independent in their movements while foraging around a male’s territory, they are frequently joined by the territory holder. This is when and how mating occurs. By accepting copulation from the territory holder, females perhaps are not as “interested” in his particular qualities as they are in gaining good access to the food that is available around (Leuthold 1978). Any prolonged bond with the male is of little importance, for he does not participate in caring for the young (Leuthold 1977). Females have an advantage of associating with territorial males because by doing so, they gain a safer and less disturbed feeding environment. A larger congregation of animals at one place may confuse predators; one gerenuk could also warn the rest of the group about an imminent danger by emitting a “low short buzz.” Also, gazelles in general walk up to the perceived predator in order to alert others and to assess the threat. The decision whether to start running or not will be based on the type of predator and the distance that separates it from the gazelle (Burnie 2005). Protection from harassment on the part of subadult males could also be a factor that determines the female’s mating strategy (Leuthold 1978).
The male is more concerned about keeping his territory than about following a particular female group. His strategy is to defend the resources, not the females (the “resources” here refer to generally safer surroundings; food patch quality may also differ, especially when fire has reduced the abundance of young shoots). However, he does that in order to attract the females. As Owen-Smith (1977) suggests, it is unlikely that territorial exclusion brings the territory-holding individual the benefit of an increased food supply. On the other hand, there is a reproductive gain, which varies between 1.5 and 3 times, depending on the ratio of territorial to bachelor males. It is to be noted as well that reproduction in gerenuks is not seasonal (Leuthold 1978, “Ecology”), so the male would be losing a lot of potential mates which are available year-round if he were to stick to one partner.
Parent/offspring relationships:
Courtesy of Liz Leiden, www.v-liz.com
The gerenuk belongs to the “hiding” type of ungulates, meaning that the fawn does not follow the mother around during her daily movements, but instead lies down and hides in a place of tall vegetation, patiently awaiting its mother and nursing time. This hiding behavior is observed until the age of 4 months. During the day, the fawn hides near bushes and small trees, while at night it avoids predation by sleeping in piles of dry branches (Klingel 1991). The young gerenuk actively chooses the hiding spot itself, and the mother rarely influences its choice. It is probable that the fawn has an innate tendency to respond to tall objects that may be good for hiding. When the mother leaves her little one in search of food, she retains an excellent memory of its exact location and has no problem finding it later (Leuthold 1977). She comes back twice during each 24-hr period to nurse it (Klingel 1991), then emits a low call that attracts the attention of the fawn, which gets up and comes to suckle (Leuthold 1977).
Subadult males and the gerenuk sex ratio:
Even though youngsters often wander alone, they also tend to group together with their peers and with females and so need to learn how to reduce group tension. They partially achieve that through sticking to a group of individuals that are about their age. Those individuals might be their siblings or unrelated gerenuks. In addition, subadults have a specific way of demonstrating submission. A young male gerenuk visually acknowledges the other's dominant status by curling his tail high over the back (Leuthold 1977). Subadults also engage in mock agonistic situations, probably to help them prepare for "real-life" aggression when they mature. The relatively high mortality of young males, caused by their frequent roaming on their own, may explain female prevalence in the gerenuk sex ratio (Leuthold 1978).
Courtesy of Liz Leiden, www.v-liz.com
Cooperative behavior and interindividual bonds:
Cooperation in ungulates, the gerenuk included, is relatively rare. The elephant is a remarkable exception to this rule. Another difference between species such as the gerenuk, on one hand, and the plains zebra and the elephant, on the other, is the more prominent leadership behavior in the latter. Male gerenuks only follow groups with females; they don’t actively lead them. Elephants and zebra, in contrast, show many instances of one individual leading the entire group. The reasons for the lack of such behavior in the gerenuk possibly stem from the relative fluidity of the small gerenuk group, the lack of extensive daily movement (which would require a clear sense of common direction and antipredator strategies), as well as, perhaps, the shorter lifespan of the tiny gazelle. The long-lived elephants have plenty of years to get to know one another as individuals and to establish bonds, which “appear to favor the “concentration” of leadership in certain individuals” (Leuthold 1977).
Allogrooming is another rare behavior in adult gerenuks, probably because the species is not very gregarious, so that strengthening of the bonds between individuals is of little importance. This may not be so in captive conditions, where animals generally inhabit a more limited space together. Leuthold (1977) writes that while his colleagues have observed many instances of allogrooming in captive gerenuks, he himself has never observed one in the wild, except in the context of mother-young interactions. He suggests that in zoos, where food pressures and predator threats are absent, certain other behaviors – such as mutual grooming, play, and sexual behavior – are exhibited far more often than normal.
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