Robin L. Mackey

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.

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.

The effects of herbivory by a mega- and mesoherbivore on tree recruitment in sand forest, South Africa.

Herbivory by megaherbivores on woody vegetation in general is well documented; however studies focusing on the individual browsing effects of both mega- and mesoherbivore species on recruitment are scarce. We determined these effects for elephant Loxodonta africana and nyala Tragelaphus angasii in the critically endangered Sand Forest, which is restricted to east southern Africa, and is conserved mainly in small reserves with high herbivore densities. Replicated experimental treatments (400 m2) in a single forest patch were used to exclude elephant, or both elephant and nyala. In each treatment, all woody individuals were identified to species and number of stems, diameter and height were recorded. Results of changes after two years are presented. Individual tree and stem densities had increased in absence of nyala and elephant. Seedling recruitment (based on height and diameter) was inhibited by nyala, and by elephant and nyala in combination, thereby preventing recruitment into the sapling stage. Neither nyala or elephant significantly reduced sapling densities. Excluding both elephant and nyala in combination enhanced recruitment of woody species, as seedling densities increased, indicating that forest regeneration is impacted by both mega- and mesoherbivores. The Sand Forest tree community approached an inverse J-shaped curve, with the highest abundance in the smaller size classes. However, the larger characteristic tree species in particular, such as Newtonia hildebrandtii, were missing cohorts in the middle size classes. When setting management goals to conserve habitats of key importance, conservation management plans need to consider the total herbivore assemblage present and the resulting browsing effects on vegetation. Especially in Africa, where the broadest suite of megaherbivores still persists, and which is currently dealing with the ‘elephant problem’, the individual effects of different herbivore species on recruitment and dynamics of forests and woodlands are important issues which need conclusive answers.

Modelling the effect of age-specific mortality on elephant Loxodonta africana populations: can natural mortality provide regulation?

Leigh-Ann Woolley, Robin L. Mackey, Bruce R. Page and Rob SlotowAbstract The historical regulation of African elephantLoxodonta africana populations could provide guidelinesfor management efforts and decisions in areas whereelephant numbers are now increasing. However, thereare few detailed records of the natural mortality pro-cesses of the past. Therefore, we modelled elephantpopulation growth to evaluate possible effects of age-specific mortality. Model projections indicated that anannual mortality of 17.1% of juveniles or 10.5% of adultswould be sufficient to prevent population growth. Forage classes below or just at sexual maturity (i.e. 0-3, 4-7,8-11) 37.5% annual mortality of one of these classes wasrequired to achieve 0% population growth. These mor-tality levels are much higher than those reported insouthern Africa today. Simulations of episodic mortalityevents (e.g. droughts) indicated that such events wouldneed to occur every 16 years at a severity that wouldcause the mortality of all infants and weaned calves (0-7years old), as well as 10% of adults and subadults (8-60years old) to prevent long-term population growth. An8-year frequency required the mortality of 84.7% ofinfants and weaned calves. Historically, it is possiblethat highdroughtmortality andfrequency,andhighpre-dation levels, may have reduced population growthsignificantly but current mortality rates and frequenciesare insufficient to constrain long-term average popula-tion growth at 0%. The natural limitation of existentelephant populations through mortality is therefore un-likely, indicating a need for active management of theincreasing elephant populations in southern Africa.Keywords Demography, elephant management,growth rates, Loxodonta africana, mortality, populationmodel, southern Africa.IntroductionThere is concern over the current rate of increase ofAfricanelephantLoxodonta africana populations insouth-ern Africa. Past maximum annual elephant growth rateshave been estimated at up to 7% (Hanks & McIntosh,1973; Calef, 1988) but more recent studies indicate thatshort-term rates of growth can be much higher. VanJaarsveld et al. (1999) calculated average annual growthrates of up to 15%, and Mackey et al. (2006) showed thatannual growth rates of 10-15% were not uncommon innature reserves in South Africa.Up to the mid 1990s culling was promoted as a man-agement tool for elephant populations confined to con-servation areas in southern Africa (Buechner et al., 1963;Glover, 1963; van Wyk & Fairall, 1969). However, there isnow again debate over the impact of high numbers ofelephants and the possible need to reduce populations.This creates a conservation dilemma, with the impact ofhigh elephant densities on biodiversity being in contrastwith the elephant’s more precarious status beyondsouthern Africa (Baxter & Getz, 2005; Mabunda, 2005;Owen-Smith et al., 2006). The lack of evidence fordensity dependent responses in elephant populations(Gough & Kerley, 2006) suggests the current high ratesof population growth may not slow down under naturalconditions. Although density feedbacks must inevitablyinfluence population growth, it is uncertain at whichstage this occurs in different elephant systems (Owen-Smith et al., 2006). Maximum population growth rate canbe maintained in large-bodied mammals until the pointwhen forage resources can no longer support thepopulation (Fowler & Smith, 1973; Fowler, 1981). How-ever, because of their long generation times elephantpopulations can lag in their response to changing forageavailability, theoretically causing oscillations in the num-bers of elephants and forage rather than the achieve-ment of an equilibrium (Caughley, 1976).The direct study of long-term mortality is difficult ina long-lived mammal and few studies have documentedelephantpopulationsoveralongtimescale(WhitehouseHMoss,2001;Wittemyer,2001;Wittemyeret al., 2005). Natural mortality in large, well-established,free-ranging elephant populations is age-dependent, with

How immunocontraception can contribute to elephant management in small, enclosed reserves: Munyawana population as a case study.

Immunocontraception has been widely used as a management tool to reduce population growth in captive as well as wild populations of various fauna. We model the use of an individual-based rotational immunocontraception plan on a wild elephant, Loxodonta africana, population and quantify the social and reproductive advantages of this method of implementation using adaptive management. The use of immunocontraception on an individual, rotational basis stretches the inter-calving interval for each individual female elephant to a management-determined interval, preventing exposing females to unlimited long-term immunocontraception use (which may have as yet undocumented negative effects). Such rotational immunocontraception can effectively lower population growth rates, age the population, and alter the age structure. Furthermore, such structured intervention can simulate natural process such as predation or episodic catastrophic events (e.g., drought), which regulates calf recruitment within an abnormally structured population. A rotational immunocontraception plan is a feasible and useful elephant population management tool, especially in a small, enclosed conservation area. Such approaches should be considered for other long-lived, social species in enclosed areas where the long-term consequences of consistent contraception may be unknown.