Kevin J. Duffy

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.

Landscape-scale feeding patterns of African elephant inferred from carbon isotope analysis of feces

The African elephant (Loxodonta africana) is a large-bodied, generalist herbivore that eats both browse and grass. The proportions of browse and grass consumed are largely expected to reflect the relative availability of these resources. We investigated variations in browse (C3 biomass) and grass (C4) intake of the African elephant across seasons and habitats by stable carbon isotope analysis of elephant feces collected from Kruger National Park, South Africa. The results reflect a shift in diet from higher C4 grass intake during wet season months to more C3 browse-dominated diets in the dry season. Seasonal trends were correlated with changes in rainfall and with nitrogen (%N) content of available grasses, supporting predictions that grass is favored when its availability and nutritional value increase. However, switches to dry season browsing were significantly smaller in woodland and grassland habitats where tree communities are dominated by mopane (Colophospermum mopane), suggesting that grasses were favored here even in the dry season. Regional differences in diet did not reflect differences in grass biomass, tree density, or canopy cover. There was a consistent relationship between %C4 intake and tree species diversity, implying that extensive browsing is avoided in habitats characterized by low tree species diversity and strong dominance patterns, i.e., mopane-dominated habitats. Although mopane is known to be a preferred species, maintaining dietary diversity appears to be a constraint to elephants, which they can overcome by supplementing their diets with less abundant resources (dry season grass). Such variations in feeding behavior likely influence the degree of impact on plant communities and can therefore provide key information for managing elephants over large, spatially diverse, areas.

Stable isotope series from elephant ivory reveal lifetime histories of a true dietary generalist

Longitudinal studies have revealed how variation in resource use within consumer populations can impact their dynamics and functional significance in communities. Here, we investigate multi-decadal diet variations within individuals of a keystone megaherbivore species, the African elephant (Loxodonta africana), using serial stable isotope analysis of tusks from the Kruger National Park, South Africa. These records, representing the longest continuous diet histories documented for any extant species, reveal extensive seasonal and annual variations in isotopic—and hence dietary—niches of individuals, but little variation between them. Lack of niche distinction across individuals contrasts several recent studies, which found relatively high levels of individual niche specialization in various taxa. Our result is consistent with theory that individual mammal herbivores are nutritionally constrained to maintain broad diet niches. Individual diet specialization would also be a costly strategy for large-bodied taxa foraging over wide areas in spatio-temporally heterogeneous environments. High levels of within-individual diet variability occurred within and across seasons, and persisted despite an overall increase in inferred C4 grass consumption through the twentieth century. We suggest that switching between C3 browsing and C4 grazing over extended time scales facilitates elephant survival through environmental change, and could even allow recovery of overused resources.

Heavy impact on seedlings by the impala suggests a central role in woodland dynamics

Research has increasingly established that mesoherbivores influence the regeneration of woody plants. However the relationship between mesoherbivore density and degree of impact, and the spatial component of this impact, has not been well established. Using a novel sampling design, we assessed in iMfolozi Park, South Africa, the impactofimpala(Aepycerosmelampus)acrossthefullcomplementofwoodyspecieswithinthehomerange,evaluating its spatial component and relationship to impala density. We used four GPS collars, in separate breeding herds, and a GIS to detect zones of different density of impala in the landscape, thus defining a fine-grain browsing gradient. We assessed impact on woody recruits (≤0.5 m height) across this gradient by means of 1600 random 1 ×1-m quadrats. Densitiesofwoodyseedlings,andmeanpercentageofremainingcanopy,weresignificantlylessinareasofhighimpala densityversuslow-densityareas.Therewasasignificantcorrelationbetweenincreasingimpaladensityanddecreasing density of favoured woody recruits. We propose a hypothesis of impala-induced patch dynamics. It seems likely that the ubiquitous impala may create and sustain a shifting mosaic of patches, and thus function as a key determinant of landscape heterogeneity.

Using Maximum Entropy modeling to predict the potential distributions of large trees for conservation planning

Large trees, as keystone structures, are functionally important in savanna ecosystems, and low recruitment and slow growth makes their conservation important. Understanding factors influencing their distribution is essential for mitigation of excessive mortality, for example from management fires or large herbivores. We recorded the locations of large trees in Hluhluwe-Imfolozi Park (HiP) using GPS to record trees along 43 km of 10 m-wide transects. Maximum entropy modeling (MaxEnt) uses niche modeling to predict the distribution of a species from the probability of finding it within raster squares, based on environmental variables and recorded locations. MaxEnt is typically applied at a regional spatial scale, and here we assessed its usefulness when predicting the distribution of species at a small (local) scale. HiP has variable topography, heterogeneous soils, and a strong rainfall gradient, resulting in a wide variety of habitat types. We used locations of 179 Acacia nigrescens and 106 Sclerocarya birrea (large trees ≥ 5m), and raster environmental layers for: aspect, elevation, geology, annual rainfall, slope, soil and vegetation. A. nigrescens was largely restricted to the Imfolozi section, while S. birrea had a wider distribution across the reserve. Understanding the interaction of environmental variables dictating tree distribution may facilitate habitat restoration, and will assist planning decisions for persistence of large trees within reserves, including options to reduce fire frequency or herbivore impacts. Though the AUC (Area Under the Curve) values used to test model predictions were high for both species, the ground truthing test data showed that distribution for A. nigrescens was more accurate than that for S. birrea, highlighting the need for independent test data to assess model accuracy. We emphasize that MaxEnt can be used at finer spatial scales than those typically used for species occurrence, but models must be tested using spatially independent test data.

The consequences of body size dimorphism: are African elephants sexually segregated at the habitat scale?

Sexual segregation is a commonly observed phenomenon in dimorphic ungulates, which has been categorised into two distinct components: social segregation and habitat segregation. In this study we investigated whether elephants were sexually segregated at the habitat scale. The locations of 12 family groups and 16 males, in three distinct populations were recorded over a period of 2.5 years. Selection ratios were calculated for each habitat type and a Kendalls coefficient of concordance was used for the analyses. The habitat and foraging preferences were firstly tested for concordance within sex, and then between the sexes. Female habitat preferences showed significant concordance across all reserves and they also exhibited strong concordance in their summer foraging preferences. Their weakest association with habitat and foraging preference was during winter, which may be related to resource scarcity. Males exhibited significant concordance in their habitat preferences in two out of the three reserves. They had their weakest associations in the summer months and this may be linked to avoidance of other males in musth and the abundance of forage. There were no significant differences in habitat preference between males and females and it is likely that individual preferences vary as much within sex as between sexes. Differential habitat utilisation does not appear to be driving sexual segregation in elephants and it is postulated that sociality, divergent reproductive strategies and foraging behaviour at the plant scale play a more significant role. The results of this study highlight the importance of scale in elucidating the mechanisms involved in sexual segregation.

Movement Patterns of African Elephants (Loxodonta africana) in Different Habitat Types

In this paper we analyse the daytime movements of African elephants (Loxodonta africana) in different habitats in the Pongola Game Reserve, South Africa. On average adult males moved faster than females in all habitat types except when grouped together (then females moved at the faster male pace). Elephants demonstrated distinct movement patterns in different habitat types. All the movement parameters indicate that the elephants turned less the further they were from a large permanent body of water (Jozini Dam) and for males with increasing distance to the females. Male and female elephants turned more in habitat types that had favourable resources such as forage and shade, than they did in unfavourable habitats. Thus, the elephants used a direct movement strategy — turning less — when needing to get to a destination more quickly (e.g. toward water or mates), rather than significantly increasing their speed. It is hypothesized that these elephants are optimizing energy efficiency while still varying their foraging approach and search intensity. Patterns of movement through a habitat will affect ecological impacts in that habitat and so habitat-related movement pattern studies of this type could assist landscape planning (e.g. waterhole design and distribution) and large herbivore conservation.