Laurence G. Frank

Social organization of the spotted hyaena Crocuta crocuta. II. Dominance and reproduction

Abstract A 4-year study of the social organization of spotted hyaenas in a clan of 60–80 individuals showed that there is a separate dominance hierarchy within each sex. One female and her descendants dominated all others; matrilineal rankings were stable over time because maternal rank is inherited. Cubs of higher ranking females were able to feed at kills in competition with adults more successfully than other cubs, and male offspring of the alpha female were the only males able to dominate adult females. The mating system is highly polygynous: only the behaviourally dominant male was seen to mate, though all other resident males regularly courted females. Among females, there was no correlation between reproductive success and age, size, or social rank. It is postulated that the unusually aggressive sons of the alpha female would probably be highly successful competitors in the context of a polygynous mating system. A primary consequence of female dominance over males is that females and their young have priority of access to food in a highly competitive feeding situation. This competition may have been the selective force that produced female dominance and the associated syndrome of female virilization that is characteristic of the species. Cooperation among related females may be the basis for the matrilineal system, as has been suggested for certain primate species.

Lethal control of African lions (Panthera leo): local and regional population impacts

Large carnivores have declined worldwide, largely through conflict with people. Here, we quantify the impact of lethal control, associated with livestock depredation, on a population of African lions (Panthera leo )l iving outside protected areas. Farmers shot lions only in response to livestock attacks. Nevertheless, adult mortality was high and a simple model predicted that the population was marginally stable or slowly declining. Mortality was four times higher among lions radio-collared in association with attacks on livestock, than among lions with no known history of stock killing, suggesting that some animals were habitual stock killers. Known stock killers also experienced lower reproductive success; hence there was strong artificial selection against stockkilling behaviour. In addition, mortality was higher among lions whose home ranges overlapped a property where non-traditional livestock husbandry was associated with chronic depredation by lions. This 180 km 2 ranch acted as a sink that directly affected lions over more than 2000 km 2 and may have undermined the viability of the study population. Our results suggest that sustainable coexistence of lions and people demands livestock husbandry that effectively deters predators from acquiring stock-killing behaviour, but that lethal control may play an important role in avoiding the spread of such behaviours through the population.

Patterns of Association among Female Spotted Hyenas (Crocuta crocuta)

We examined subgroup association patterns among adult female members of a clan of free-living spotted hyenas ( Crocuta crocuta ) and between adult females and their juvenile offspring during three consecutive stages of development of offspring. These stages represented the approximate periods of residence of offspring at the communal den, from 1 to 8 months of age, between leaving the communal den and weaning, from 8 to 14 months, and between weaning and reproductive maturity or dispersal, from 14 to 36 months of age. Mean association indices among adult female dyads varied with social rank, with the highest mean association index observed for the alpha female. Adult females associated more closely with their adult female kin than with unrelated adult females. Female kin from high-ranking matrilines associated more closely than did kin from lower-ranking matrilines. Within mother-offspring pairs, association patterns were strongly influenced by the mothers social rank during all three stages of development of offspring, with high-ranking mother-offspring dyads associating more tightly than low-ranking dyads at each stage. Mean mother-offspring association indices declined as offspring grew older, but we found no significant differences based on sex of offspring during any of the developmental stages examined.

Social organization of the spotted hyaena (Crocuta crocuta). I: Demography

A 4-year field study of one group of 60–80 spotted hyaenas (Crocuta crocuta) in Kenyas Masai Mara National Reserve has revealed a form of social system undescribed among carnivores but common among primates. Male juveniles disperse from the natal group around puberty and join a population of nomadic males, wandering widely before settling in a new clan. Adult males frequently leave their adopted clan after a variable period of residence. Females remain in their natal group for life. Thus, the clan comprises several matrilines of related females, while resident adult males originate outside the group. Clans in the Mara tend to be separated by wide buffer zones where prey is scarce and boundary maintenance behaviours are relatively uncommon. Transients are subordinate to residents, but are tolerated by them, in contrast to the more territorial clan system that has been described in Ngorongoro Crater.

Efficacy of Two Lion Conservation Programs in Maasailand, Kenya

Lion (Panthera leo) populations are in decline throughout most of Africa. The problem is particularly acute in southern Kenya, where Maasai pastoralists have been spearing and poisoning lions at a rate that will ensure near term local extinction. We investigated 2 approaches for improving local tolerance of lions: compensation payments for livestock lost to predators and Lion Guardians, which draws on local cultural values and knowledge to mitigate livestock-carnivore conflict and monitor carnivores. To gauge the overall influence of conservation intervention, we combined both programs into a single conservation treatment variable. Using 8 years of lion killing data, we applied Manskis partial identification approach with bounded assumptions to investigate the effect of conservation treatment on lion killing in 4 contiguous areas. In 3 of the areas, conservation treatment was positively associated with a reduction in lion killing. We then applied a generalized linear model to assess the relative efficacy of the 2 interventions. The model estimated that compensation resulted in an 87-91% drop in the number of lions killed, whereas Lion Guardians (operating in combination with compensation and alone) resulted in a 99% drop in lion killing.

Evolution of a Major Drug Metabolizing Enzyme Defect in the Domestic Cat and Other Felidae: Phylogenetic Timing and the Role of Hypercarnivory

The domestic cat (Felis catus) shows remarkable sensitivity to the adverse effects of phenolic drugs, including acetaminophen and aspirin, as well as structurally-related toxicants found in the diet and environment. This idiosyncrasy results from pseudogenization of the gene encoding UDP-glucuronosyltransferase (UGT) 1A6, the major species-conserved phenol detoxification enzyme. Here, we established the phylogenetic timing of disruptive UGT1A6 mutations and explored the hypothesis that gene inactivation in cats was enabled by minimal exposure to plant-derived toxicants. Fixation of the UGT1A6 pseudogene was estimated to have occurred between 35 and 11 million years ago with all extant Felidae having dysfunctional UGT1A6. Out of 22 additional taxa sampled, representative of most Carnivora families, only brown hyena (Parahyaena brunnea) and northern elephant seal (Mirounga angustirostris) showed inactivating UGT1A6 mutations. A comprehensive literature review of the natural diet of the sampled taxa indicated that all species with defective UGT1A6 were hypercarnivores (>70% dietary animal matter). Furthermore those species with UGT1A6 defects showed evidence for reduced amino acid constraint (increased dN/dS ratios approaching the neutral selection value of 1.0) as compared with species with intact UGT1A6. In contrast, there was no evidence for reduced amino acid constraint for these same species within UGT1A1, the gene encoding the enzyme responsible for detoxification of endogenously generated bilirubin. Our results provide the first evidence suggesting that diet may have played a permissive role in the devolution of a mammalian drug metabolizing enzyme. Further work is needed to establish whether these preliminary findings can be generalized to all Carnivora.

People and Wildlife: People and predators in Laikipia District, Kenya

In this century, only in Africa do substantial numbers of people and livestock still live alongside sizeable populations of large carnivores. Predators are rarely a threat to humans in modern Africa, but they are a significant source of livestock losses to both commercial and subsistence livestock producers. Killing of predators has been documented for as long as there has been literature (see Homer, The Iliad), but a small human population would have had an insignificant effect on total carnivore numbers. However, the press of a very large human population well equipped with firearms and poison has seriously reduced predators even in Africa, a relatively sparsely populated continent (Nowell and Jackson 1996; Woodroffe et al. 1997; Mills and Hofer 1998). Few protected areas are large enough to guarantee long-term survival of wide-ranging carnivores (Woodroffe andGinsberg 1998), asmost parks are small and widely separated. Inmuch of Kenya, wildlife has been eliminated as habitat is converted to cultivation. A growing bushmeat trade has eliminated wildlife from vast regions of southeast Kenya that are unsuitable for agriculture (World Wildlife Fund, 2000a). Even the semi-arid northern half of the country, sparsely populated and once rich in wildlife, has been nearly cleared of large mammals by over-grazing, poison and the ubiquitous assault rifle. Outside protected areas, substantial predator populations persist only in the rangelands north of Mount Kenya (particularly Laikipia District), and in the south close to the border with Tanzania.

Competition and cooperation between litter-mates in the spotted hyaena, Crocuta crocuta

Abstract The development of intra-litter competition and cooperation is described in free-living and captive spotted hyaenas. Field data were collected on dominance relations in 26 twin litters, and additional behavioural analyses were performed on different subsets of this group. Intra-litter dominance relations were assessed on the basis of the direction of aggressive and appeasement behavior patterns. In all wild litters, one cub clearly dominated the other by the time cubs were observed above-ground, at 2–3 weeks of age. Within the 17 twin litters of mixed sex, female dominance over male litter-mates was significantly more common (N = 14) than the reverse (N = 3). When males were the dominant litter-mates, they were as aggressive towards their siblings as were females. Rates of intra-litter aggression were highest in the youngest age interval observed (1–2 months), and dropped significantly the next month. Peak monthly rates of intra-litter aggression correlated significantly with maternal rank, such that offspring of low-ranking females fought more than of those high-ranking females. High levels of intra-litter cooperation were observed in the context of coalition formation, and youngster affiliated more with litter-mates than with any other hyaena. In captivity, seven twin and two triplet litters were videotaped during the first 2 months of life, and were scored for aggressive interactions. Results showed that dominance between litter-mates is established as early in development as the first day of life.

Sexual dimorphism of perineal muscles and motoneurons in spotted hyenas.

Female spotted hyenas are known for their male‐like genitalia, high levels of aggression, and dominance over males, characteristics which are attributed to exposure to elevated levels of testosterone in utero. Although the nervous system of spotted hyenas has not previously been examined, one might predict that neural systems which are sexually dimorphic in other mammals would be monomorphic in this species. Spinal motoneurons which innervate muscles associated with the phallus are located in Onufs nucleus and are more numerous in males than in females in a wide array of mammals. Onufs nucleus was examined in adult and neonatal spotted hyenas and, contrary to expectation, was found to be sexually dimorphic in the typical mammalian pattern: Males have significantly more motoneurons in Onufs nucleus than do females. This dimorphism was correlated with a previously undescribed dimorphism in the relevant target musculature. Specifically, the morphology of the bulbocavernosus muscle is distinctly different in male and female spotted hyenas. Pregnant hyenas were treated with anti‐androgen in an attempt to interfere with the actions of androgen during fetal development. Motoneuron number in Onuf??s nucleus and the morphology of the bulbocavernosus muscle were feminized in males exposed to anti‐androgen in utero.

Spatial grouping in behaviourally solitary striped hyaenas, Hyaena hyaena

We investigated spatial organization and patterns of interaction in a population of the little-known striped hyaena, Hyaena hyaena. We use the resulting data to test hypotheses of group formation that predict that female striped hyaenas will be solitary in response to overdispersion of food resources and males will be solitary in response to overdispersion of females. Based primarily on anecdotal or historical information, striped hyaenas have been described as solitary. We show that, as predicted, striped hyaenas of both sexes are behaviourally solitary. However, they form stable, polyandrous spatial groups composed of multiple males and a single female. We suggest that male coalition formation may be the result of male strategies to optimize trade-offs between the number of female ranges defended and the effectiveness of that defence when females are solitary and maintain large territories. Nevertheless, the joint male defence of a territory (of any size) containing only a single female would not be predicted by any major hypothesis for the evolution of group living, in this or any other species.