Bruce R. Page

Older bull elephants control young males

Musth is a state of heightened sexual and aggressive activity in male elephants. Between 1992 and 1997, young orphaned musth male African elephants (Loxodonta africana) that had been introduced to Pilanesberg, South Africa, killed more than 40 white rhinoceros (Ceratotherium simum). The killing ceased after six older male elephants were introduced from the relatively normal Kruger Park population. The deviant behaviour of the young Pilanesberg males was rectified by the consequent reduction in musth.

African elephant home range and habitat selection in Pongola Game Reserve, South Africa

ABSTRACT The ranging behaviour and habitat occupancy by three elephant groups (cow herd, bulls, and an orphan group) were studied over a two-year period in a small, fenced reserve. No summer dispersal was observed. Distinct seasonal home ranges were exhibited for all groups, with the summer (wet season) ranges being smaller than the winter (dry season) ranges. Home range size was much smaller than in other locations. The dam and surrounding high density of patches of vegetation of high nutritional quality are thought to be the reasons. Habitat selection was strongly evident with all of the elephant groups selecting River Line habitats in the dry season. In the wet season the cow herd and orphans selected the more open Acacia habitats and the bulls exhibited no significant habitat preference.

The role of foraging behaviour in the sexual segregation of the African elephant

Elephants (Loxodonta africana) exhibit pronounced sexual dimorphism, and in this study we test the prediction that the differences in body size and sociality are significant enough to drive divergent foraging strategies and ultimately sexual segregation. Body size influences the foraging behaviour of herbivores through the differential scaling coefficients of metabolism and gut size, with larger bodied individuals being able to tolerate greater quantities of low-quality, fibrous vegetation, whilst having lower mass-specific energy requirements. We test two distinct theories: the scramble competition hypothesis (SCH) and the forage selection hypothesis (FSH). Comprehensive behavioural data were collected from the Pongola Game Reserve and the Phinda Private Game Reserve in South Africa over a 2.5-year period. The data were analysed using sex as the independent variable. Adult females targeted a wider range of species, adopted a more selective foraging approach and exhibited greater bite rates as predicted by the body size hypothesis and the increased demands of reproductive investment (lactation and pregnancy). Males had longer feeding bouts, displayed significantly more destructive behaviour (31% of observations, 11% for females) and ingested greater quantities of forage during each feeding bout. The independent ranging behaviour of adult males enables them to have longer foraging bouts as they experience fewer social constraints than females. The SCH was rejected as a cause of sexual segregation due to the relative abundance of low quality forage, and the fact that feeding heights were similar for both males and females. However, we conclude that the differences in the foraging strategies of the sexes are sufficient to cause spatial segregation as postulated by the FSH. Sexual dimorphism and the associated behavioural differences have important implications for the management and conservation of elephant and other dimorphic species, with the sexes effectively acting as distinct “ecological species”.

Activity Budgets and Sexual Segregation in African Elephants (Loxodonta africana)

Abstract The activity budget hypothesis is 1 of 4 main hypotheses proposed to explain sexual segregation by large herbivores. Because of their smaller body size, females are predicted to have higher mass-specific energy requirements and lower digestive efficiency than males. As a result, females are expected to forage longer to satisfy their nutritional demands. Maintaining the cohesion of a mixed-sex group with differing activity budgets and asynchronous behavioral patterns is increasingly difficult, ultimately leading to spatial segregation of males and females. We tested this hypothesis using data (2002–2005) from 3 distinct populations of African elephants (Loxodonta africana), a species that exhibits marked sexual segregation. Group and individual behaviors were assessed at discrete points in time throughout the day, with a minimum of 10 min between consecutive records. Focal samples of individual male and female elephants also were recorded, with behavioral data logged every minute for 15 min. Data were grouped into 5 behavioral categories: drinking, resting, walking, feeding, and other. Neither activity rhythms nor feeding time varied significantly between the sexes and behavioral patterns were very similar. We propose that social and environmental factors influence behavioral rhythms to a greater extent than does body size, whereas increasing feeding time is only 1 method by which elephants can improve nutritional return. This is especially pertinent when considering their generalist foraging approach, substantial energy demands, and hindgut fermentation. We conclude that the activity budget hypothesis is unlikely to be the causal mechanism in the sexual segregation of African elephants, a finding that concurs with recent experimental and field research on a range of sexually dimorphic herbivores.

SHORT-DURATION DAYTIME MOVEMENTS OF A COW HERD OF AFRICAN ELEPHANTS

Abstract We examined daytime movements of a herd of African elephants (Loxodonta africana) at 10-min, 15-min, and 20-min intervals in Pongola Game Reserve, South Africa. This group tended to proceed in a consistent direction during consecutive movements, especially during long moves. Serial movement lengths and serial movement angles were autocorrelated at 10-min and 15-min intervals but not at 20-min intervals, indicating that 20-min intervals may be a suitable temporal scale to avoid oversampling. Herd movements followed a Lévy-modulated correlated random walk. In addition, looping movements were detected. Spatial scale of the loops averaged about 1 km. Movement strategies that include both Lévy walks and correlated random walks are thought to optimize foraging.

Soil nutrient status determines how elephant utilize trees and shape environments

1. Elucidation of the mechanism determining the spatial scale of patch selection by herbivores has been complicated by the way in which resource availability at a specific scale is measured and by vigilance behaviour of the herbivores themselves. To reduce these complications, we studied patch selection by an animal with negligible predation risk, the African elephant. 2. We introduce the concept of nutrient load as the product of patch size, number of patches and local patch nutrient concentration. Nutrient load provides a novel spatially explicit expression of the total available nutrients a herbivore can select from. 3. We hypothesized that elephant would select nutrient-rich patches, based on the nutrient load per 2500 m(2) down to the individual plant scale, and that this selection will depend on the nitrogen and phosphorous contents of plants. 4. We predicted that elephant would cause more adverse impact to trees of lower value to them in order to reach plant parts with higher nutrient concentrations such as bark and root. However, elephant should maintain nutrient-rich trees by inducing coppicing of trees through re-utilization of leaves. 5. Elephant patch selection was measured in a homogenous tree species stand by manipulating the spatial distribution of soil nutrients in a large field experiment using NPK fertilizer. 6. Elephant were able to select nutrient-rich patches and utilized Colophospermum mopane trees inside these patches more than outside, at scales ranging from 2500 down to 100 m(2) . 7. Although both nitrogen and phosphorus contents of leaves from C. mopane trees were higher in fertilized and selected patches, patch choice correlated most strongly with nitrogen content. As predicted, stripping of leaves occurred more in nutrient-rich patches, while adverse impact such as uprooting of trees occurred more in nutrient-poor areas. 8. Our results emphasize the necessity of including scale-dependent selectivity in foraging studies and how elephant foraging behaviour can be used as indicators of change in the availability of nutrients.

Intraspecific Strategic Responses of African Elephants to Temporal Variation in Forage Quality

Abstract Mammalian herbivores adopt foraging strategies to optimize nutritional trade-offs against restrictions imposed by body size, nutritional requirements, digestive anatomy, physiology, and the forage resource they exploit. Selective or generalist feeding strategies scale with body size across species. However, within species, where constraints should be most similar, responses to limitation have rarely been examined. We used African elephants (Loxodonta africana) to test for changes in seasonal diet quality of individuals of differing body size and sex through measurement of fecal nitrogen and phosphorus. We measured physiological stress response of these age and sex classes to seasonal change by fecal glucocorticoid metabolite levels (i.e., stress hormones). Large body size increased tolerance to lower-quality forage. Adult males and females exhibited divergent trends; females had higher diet quality than males, irrespective of body size. When limited by forage availability or quality during the dry season, diet quality declined across all body sizes, but weaned calves ingested a higher-quality diet than larger-bodied adults. On release from restriction during the wet season, weaned calf nitrogen concentrations were consistently high and stress hormone levels decreased, whereas adult female phosphorus levels were highest and less variable and stress hormone levels were unchanged. The ability to adjust forage quality is an important strategy used to ensure adequate nutritional intake according to body size limitations. Although body size is a key determining factor of dietary differences between adult elephants, foraging strategies are also driven by specific nutritional requirements, which may override the body size effects driving foraging decisions in some cases. The diversity of intraspecific response highlights ecologically segregated entities within a species and should be a concern for population management planning, particularly for threatened species. Fecal diet quality and stress hormone analysis could provide an early and sensitive indicator for monitoring age and sex class responses to resource restriction in high-density elephant populations.

Risk and Ethical Concerns of Hunting Male Elephant: Behavioural and Physiological Assays of the Remaining Elephants

Background Hunting of male African elephants may pose ethical and risk concerns, particularly given their status as a charismatic species of high touristic value, yet which are capable of both killing people and damaging infrastructure. Methodology/Principal Findings We quantified the effect of hunts of male elephants on (1) risk of attack or damage (11 hunts), and (2) behavioural (movement dynamics) and physiological (stress hormone metabolite concentrations) responses (4 hunts) in Pilanesberg National Park. For eleven hunts, there were no subsequent attacks on people or infrastructure, and elephants did not break out of the fenced reserve. For three focal hunts, there was an initial flight response by bulls present at the hunting site, but their movements stabilised the day after the hunt event. Animals not present at the hunt (both bulls and herds) did not show movement responses. Physiologically, hunting elephant bulls increased faecal stress hormone levels (corticosterone metabolites) in both those bulls that were present at the hunts (for up to four days post-hunt) and in the broader bull and breeding herd population (for up to one month post-hunt). Conclusions/Significance As all responses were relatively minor, hunting male elephants is ethically acceptable when considering effects on the remaining elephant population; however bulls should be hunted when alone. Hunting is feasible in relatively small enclosed reserves without major risk of attack, damage, or breakout. Physiological stress assays were more effective than behavioural responses in detecting effects of human intervention. Similar studies should evaluate intervention consequences, inform and improve best practice, and should be widely applied by management agencies.

Realistic parameter assessment for a well known elephant-tree ecosystem model reveals that limit cycles are unlikely

Abstract In 1976 Caughley proposed a simple predator–prey model for elephant–tree dynamics. To our knowledge no-one has attempted to assess this model against real data. The significance of Caughley’s model was to show that limit cycle behavior is possible for the elephant-tree system. Using realistic parameter estimates the paper emphasizes that, in fact, limit cycles are highly unlikely. For a wide range of realistic parameter estimates the model predicts a fixed point equilibrium between elephant and trees. Equilibrium model results are compared to real data for systems where there is a strong dependence between elephant and a dominant tree species. These results compare well giving added confidence in the biological premises of the model. Reasonable variations in parameter values change the equilibrium points in explainable ways. The conclusion is that this model, while crude, is realistic for certain ecological situations and can provide useful insights into such ecosystems.

Population and individual elephant response to a catastrophic fire in Pilanesberg National Park.

In predator-free large herbivore populations, where density-dependent feedbacks occur at the limit where forage resources can no longer support the population, environmental catastrophes may play a significant role in population regulation. The potential role of fire as a stochastic mass-mortality event limiting these populations is poorly understood, so too the behavioural and physiological responses of the affected animals to this type of large disturbance event. During September 2005, a wildfire resulted in mortality of 29 (18% population mortality) and injury to 18, African elephants in Pilanesberg National Park, South Africa. We examined movement and herd association patterns of six GPS-collared breeding herds, and evaluated population physiological response through faecal glucocorticoid metabolite (stress) levels. We investigated population size, structure and projected growth rates using a simulation model. After an initial flight response post-fire, severely injured breeding herds reduced daily displacement with increased daily variability, reduced home range size, spent more time in non-tourist areas and associated less with other herds. Uninjured, or less severely injured, breeding herds also shifted into non-tourist areas post-fire, but in contrast, increased displacement rate (both mean and variability), did not adjust home range size and formed larger herds post-fire. Adult cow stress hormone levels increased significantly post-fire, whereas juvenile and adult bull stress levels did not change significantly. Most mortality occurred to the juvenile age class causing a change in post-fire population age structure. Projected population growth rate remained unchanged at 6.5% p.a., and at current fecundity levels, the population would reach its previous level three to four years post-fire. The natural mortality patterns seen in elephant populations during stochastic events, such as droughts, follows that of the classic mortality pattern seen in predator-free large ungulate populations, i.e. mainly involving juveniles. Fire therefore functions in a similar manner to other environmental catastrophes and may be a natural mechanism contributing to population limitation. Welfare concerns of arson fires, burning during “hot-fire” conditions and the conservation implications of fire suppression (i.e. removal of a potential contributing factor to natural population regulation) should be integrated into fire management strategies for conservation areas.