When selecting prey, carnivores optimise energy gained when consuming prey against energy spent when pursuing and subduing prey. Additionally, predators seem to preferentially predate on prey which presents a low risk of injury. When defending itself against predators, baboons (Papio spp.) can inflict serious injury and cause mortality. Although part of Africa’s large carnivores’ diet, predation on baboons is usually avoided. We investigated prey selection patterns of African wild dogs (Lycaon pictus) in Mana Pools National Park, Zimbabwe. Based on direct and indirect observations and analyses of faecal samples, we show that baboons form a substantial part of the African wild dog diet and were more frequently predated on than would be expected based on availability. Predation on baboons did not vary over baboon sex or age classes but was affected by seasonality. This is the first study to describe a preference for predation on this unusual prey species.
For most mammalian predators prey size increases with body size, with small carnivores (<20 kg) predating on prey smaller than themselves and large carnivores (>20 kg) predating on prey their own size or larger (Carbone et al., 1999, 2007). Although a shift from small to large prey increases energy intake, pursuing and subduing large prey requires more energy and therefore results in an increase in energy expenditure. Consequently, carnivores have developed several behavioural and ecological strategies to optimise energy intake and expenditure (Carbone et al., 2007). African wild dogs (Lycaon pictus) are social coursing predators with a body mass of ca. 25 kg (Carbone et al., 2007 (S1)). By hunting cooperatively in packs the species is able to reduce foraging costs and pursue and subdue prey much larger than their own body size (Creel & Creel, 2002; Radloff & du Toit, 2004). African wild dogs generally predate on antelopes within a body mass range of 16–32 kg and 120–140 kg (Hayward et al., 2006a). Preferred prey species in east and southern Africa are greater kudu (Tragelaphus strepsiceros), Thomson’s gazelle (Gazella thomsonii), impala (Aepyceros melampus) and bushbuck (Tragelaphus scriptus) (Hayward et al., 2006a).
African wild dogs hunt daily, at dusk and dawn or when sufficient moonlight is available (Estes & Goddard, 1967; Creel & Creel, 2002). The species hunts opportunistically using sight, aided by auditory and olfactory cues (Estes & Goddard, 1967; Creel & Creel, 2002). Hunting strategy varies with habitat type, with long-distance pursuits of prey by multiple individuals in a pack in open grassland habitats (Estes & Goddard, 1967), and several individual hunting attempts, which result in low individual kill rates but high pack feeding rates as prey is shared, in mixed woodland habitat (Hubel et al., 2016). As cursorial hunters, African wild dogs show a tendency to predate on the slowest individuals, e.g. young animals or animals in poor body condition (Fitzgibbon & Fanshawe, 1989; Pole et al., 2004).
While hunting, carnivores have more at stake than energetic expenditure and hunting success alone: they can get injured or killed by their prey (Mukherjee & Heithaus, 2013; Kerley, 2018). Therefore, deciding when to attack or avoid potentially dangerous prey is an important aspect of prey selection (Mukherjee & Heithaus, 2013). Like other carnivore species (Hayward et al., 2006b), African wild dogs seem to take the probability of injury into account by selecting prey species which pose minimal risk of injury and avoiding prey species which are likely to stand and defend themselves (Hayward et al., 2006a).
Baboon (Papio spp.) is a prey species which can inflict serious injury and mortality (Cowlishaw, 1994; Estes, 2004) and, where possible, Africa’s large carnivores usually avoid predation on baboons (Hayward & Kerly, 2005; Hayward, 2006; Hayward et al., 2006a, b). Baboons have occasionally been recorded as part of the African wild dog’s diet (Woodroffe et al., 2007; Mbizah et al., 2012), however, as far as we are aware, observations of hunts on this prey species have never been described (see also Cowlishaw, 1994; Hayward et al., 2006a). Although baboon lies within their preferred prey body mass range, African wild dogs seem to actively avoid predation on this dangerous prey species (Hayward et al., 2006a). In this study we investigate prey selection patterns of African wild dogs in Mana Pools National Park, Zimbabwe, and discuss which ecological factors are likely to contribute to baboon hunting by African wild dogs.
2.1. Study area
Mana Pools National Park (MPNP) is a 2196 km2 UNESCO Natural World Heritage Site in northern Zimbabwe (15°56′S, 29°27′E), managed by the Zimbabwe Parks and Wildlife Management Authority. Mean annual rainfall is ca. 706 mm with a wet season from November to March. July is the coldest month (mean minimum temperature 10.7°C), October the hottest (mean maximum temperature 39.7°C). Four main vegetation types are found in MPNP: Colophospermum mopane woodland, Faidherbia albida woodland, Brachystegia–Julbernardia woodland and Commiphora–Combretum thicket (Figure 1). MPNP is utilised for photographic safaris by vehicle, on foot or by canoe (ZPWMA, 2009).
MPNP is situated along the Zambezi river (Figure 1), which is the main permanent water source for the park. The ecology of MNNP’s large mammals is affected by a seasonal dry-season concentration of wildlife on the valley floor due to water availability and the presence of food sources due to prolonged plant productivity and availability of Faidherbia albida on the alluvial floodplains (ZPWMA, 2009). MPNP is home to all species within Africa’s large carnivore guild: lion (Panthera leo), spotted hyena (Crocuta crocuta), leopard (Panthera pardus), cheetah (Acinonyx jubatus), brown hyena (Parahyaena brunnea) and African wild dog (van der Meer, 2016), and harbours a variety of herbivore species, such as buffalo (Syncerus caffer), eland (Tragelaphus oryx), impala, greater kudu, waterbuck (Kobus ellipsiprymnus) and zebra (Equus quagga). The area is also home to a population of chacma baboons (Papio ursinus) (WEZ, 2017).
2.2. Direct and indirect observations
Data from two radio-collared African wild dog packs were collected between 2015 and 2017. These two packs were radio-collared as part of a long-term ongoing ecological study. Target animals (two within each pack) were immobilized for collaring purposes by a qualified license holder (PB), using a Dan-inject dart gun (Dan-inject, Børkop, Denmark) and a drug combination of ketamine/xylazine which was reversed with atipamezole (see Kock & Burroughs, 2012). A directional antenna was used to locate and keep track of a pack. As soon as a pack was located, continuous observations were made from a vehicle for as long as practically feasible. Whether the pack was resting or moving was monitored visually, or from motion sensors in the collars, at 5-min scan intervals. Changes in activity mode or direction were recorded, and location fixes taken by triangulation or visual observations and a GPS unit. The openness of the study area and the extensive road network, which African wild dogs use to travel and rest (Reich, 1981), usually allowed us to keep pace with the pack and follow their (hunting) movements visually and/or by radio-telemetry. When a pack made a kill, we recorded prey species killed and where possible sex and age of the prey species. In addition, we collected sightings from safari guides and operators familiar with the study packs (citizen science observations). In total we recorded 85 direct sightings and 36 citizen science sightings, which resulted in 29 prey records. Because large parts of MPNP are inaccessible during the wet season, direct observations were only made from March untill early December.
In 2015 (end of Feb, June–Dec) and 2016 (March, Aug–Nov) the British Broadcasting Corporation (BBC) joined the research team and followed the two radio-collared packs over a total of 565 days. The BBC made their ca. 320 hours of behavioural video footage available for this study. We analysed the hunt and feeding scenes in the clips and recorded prey species killed and, where possible, sex and age of the prey species. This resulted in an additional 94 prey records.
Mana Pools National Park is well known for allowing unguided game drives and walks, the park annually receives ca. 6000 visitors who are permitted to leave their vehicle and walk anywhere in the park unescorted, in groups or singly (ZPWMA, 2009). Consequently wildlife is habituated to and very relaxed about human presence (ZPWMA, 2009) and the presence of our research team and/or the BBC camera crew is ulikely to have biased the results as presented in this study. The Research Council of Zimbabwe and the Zimbabwe Parks and Wildlife Management Authority provided clearance for this study under permit no23(1) (c) (II) 36/2015: no23(1) (c) (II) 6/2016: no23(1) (c) (II) 3/2017.
2.3. Faecal samples
Hairs remain relatively undamaged during digestion; therefore, hairs extracted from carnivore faeces can be used to identify prey species (Keogh, 1983). While following the packs, we opportunistically collected scats (
We used a Pearson’s chi-square test to determine whether there was an association between the number of impala and baboon kills recorded for each pack and the data collection method: direct observations, observations from BBC footage and analyses of faecal samples. As we found no significant association (pack I:
Data on availability of prey species in the area covered by the two African wild dog packs (Figure 1) were obtained from Wildlife and Environment Zimbabwe’s annual game counts (WEZ, 2015, 2016, 2017). During these dry season counts experienced game count teams (including a Zimbabwe Parks and Wildlife game ranger) walk across the ca. 45 km2 central Mana Pools floodplain (Figure 1) on north-south transect lines which are 500 m apart and record bird, carnivore and herbivore species within the 250 m zone on either side of the transect. In two consecutive days, each transect is walked four times: twice in the early morning and twice in the late afternoon (WEZ, 2017). For each year we calculated the proportion of available African wild dog prey species along the floodplain by dividing the mean count of that species (total number counted of a prey species divided by the number of transects) by the sum of the mean count for all prey species (Table 1).
Following Hayward et al. (2006a), we used a Jacobs’ index (Jacobs, 1974) to determine whether African wild dogs predated on prey species relative to availability or whether they avoided or preferred certain prey species. The Jacobs’ index follows the equation
Using a genlin procedure, we fitted binary logistic regression models to determine which factors affect the number of baboon kills. Where appropriate we first used a non-parametric, two tailed, point-biserial correlation to test for correlations between variables. Treating impala kills as the reference, we modelled the number of baboon kills in relation to season (wet or dry), breeding season (denning: when pups are too small to follow the pack and the pack returns to the den after foraging, or nomadic: when the pups follow the pack) and time of day the kill was made (unknown, AM or PM). Because pack identity and pack size (number of adults and subadults) were significantly correlated (
We recorded a total of 113 kills by pack I (2015
The study packs more often predated on adult than subadult impalas (
The parameter time of day the kill was made did not occur in the confidence set of models and was therefore considered not to have a substantial impact on the number of baboon kills. Based on the models with the most support (Table 2), the relative importance of individual parameters (Table 3) and taking into account 85% confidence intervals of the model averaged parameter estimates, the number of baboon kills was higher in the dry season than the wet season and lower in the denning season than the nomadic season. Model averaged 85% confidence intervals for the parameter pack identity included zero (Table 3), this parameter was therefore discarded as an uninformative parameter (Arnold, 2010). During the study period, pack size (adults and subadults) varied considerably (Table A1 in the Appendix) with an overall average pack size of 16.0 ± 1.5 (mean ± SE) adults and subadults for pack I and 10.9 ± 0.4 (mean ± SE) adults and subadults for pack II. The point-biserial correlation confirmed there was no significant relationship between pack size and the number of impalas or baboons killed (
Direct observations (
Although the line transect method is a flexible and cheap method to estimate the abundance of wildlife species, it has its shortcomings (Greene, 2012). Especially when, like in this study, limitations of the data set prevent the use of distance sampling software to account for variation in detectability. Besides, because this method assumes all animals are detected at their initial location, animal movement can create bias, particularly when animals move in response to the observers (Palka & Hammond, 2001; Glennie et al., 2015). As a result of allowing unguided walks, the wildlife in MPNP is exceptionally relaxed about human presence. In addition, the floodplain consists of very open vegetation which facilitates easy detection of wildlife. Counting bias due to differences in detection ability or animal movement is therefore minimal. Game counts took place in the dry season in an area containing the main permanent water source of MPNP. Although less so for browers, distribution patterns of grazers are strongly affected by water availability (Redfern et al., 2003). The game count data set is therefore unlikely to be representative for prey abundance in MPNP as a whole. However, because the area sampled is representative for the area utilised by the African wild dog study packs (Figure 1) we do feel the game count data provides a reliable indication of relative prey availability which can be used to draw conclusions about prey selection of the two study packs.
The African wild dog packs in our study predominantly predated on impalas and baboons. Compared to impalas, which present limited threat of injury to predators (Hayward et al., 2006a, b), baboons, a prey species for which adult males especially are known to retaliate against predators, present a high risk of injury (Cowlishaw, 1994; Estes, 2004). It is challenging to accurately assess frequency of injury from dangerous prey (Mukherjee & Heithaus, 2013) and our data on frequency of baboon related injuries are limited. However, we observed several cases in which baboons defended themselves, their young, or other troop members against African wild dog attacks (Figure 4) and baboon hunts did result in injury (Figure 5). Injury is an important foraging cost (Mukherjee & Heithaus, 2013) which predators take into account by avoiding prey which presents a high risk of injury or mortality (Hayward et al., 2006a, b). However, in this study, once included in the diet, the African wild dog study packs preferred to predate on baboons.
Prey vulnerability to predation varies over age and sex classes (Cowlishaw, 1994; Pole et al., 2004) and is affected by season (Pole et al., 2004). While some studies describe adult male baboons to be most vulnerable to predation (Cowlishaw, 1994), others only found age differences in vulnerability (adults more vulnerable than subadults) (Jooste et al., 2012). The African wild dog packs in this study predated equally on male and female and adult and subadult baboons. Vulnerability of impala sex and age classes of to African wild dog predation is affected by sex ratio and season (Reich, 1981; Pole et al., 2004). In some ecosystems, overall predation is higher on adults males (Pole et al., 2004) while in other ecosystems female and adult impalas are more vulnerable to African wild dog predation (Reich, 1981; Vogel et al., 2018). Compared to males and subadults, our study packs predated more heavily on female and adult impalas. Predation on impalas increased in the wet season, baboon predation was higher in the dry season. Baboons do not have a demarcated breeding season (Cheney et al., 2004) but impalas give birth to their fawns in the wet season (Child, 1964). During this period, pregnancy and lactations reduces fat reserves of female impalas to a minimum (Pole et al., 2004). African wild dogs select young prey animals or prey in poor body condition (Fitzgibbon & Fanshawe, 1989; Pole et al., 2004) and the wet season provides an abundance of out of condition impala females and young and naïve impalas that are relatively easy to catch (Pole et al., 2004). In addition, extensive elephant movement along the muddy floodplain of MPNP results in a rugged surface of hardened, dried out, elephant footprints in the dry season, herewith increasing the difficulty of high speed pursuits of impalas and the indirect risk of injury such pursuits present (Mukherjee & Heithaus, 2013).
Baboon kills were less frequently made in the denning season when the need to feed the pups at the den can affect prey selection (Woodroffe et al., 2007). Body mass of adult impalas (adult male ca. 60 kg, adult female ca. 45 kg) is 2–3 times higher than body mass of adult baboons (adult male ca. 32 kg, adult female ca. 15.4 kg) of the same sex (Estes, 2004), a baboon kill is therefore less likely to feed the entire pack. Although African wild dogs generally consume 2–3 kg of meat per individual (Creel & Creel, 1995; Carbone et al., 2007), stomach capacity is ca. 9 kg (Creel & Creel, 1995). Consequently, predation on impalas maximizes food intake of the pack and herewith the quantity of meat which can be regurgitated for the pups upon return to the den. With larger packs being able to kill larger prey (Creel & Creel, 2002), a preference for smaller prey could be an indication of suboptimal pack sizes. However, in accordance with Woodroffe et al. (2007), we found no evidence pack size (adults + subadults) affected predation on baboons or impalas. Throughout the study, pack size of our African wild dog study packs was ⩾7 adults, which is considered a viable pack size for cooperative hunting and breeding (Courchamp et al., 2002). Therefore, an inability to secure larger prey due to suboptimal pack sizes does not explain why African wild dogs in MPNP preferentially predated on baboons.
Preferential predation on baboons also does not seem to be the result of a low availability of impalas. There are many ecosystems where impalas are the principal prey species of African wild dogs, compared to these systems, impala densities along the MPNP floodplain (37.3/km2) are relatively high (e.g., Selous 28.6/km2, Savé 11.7/km2) (Creel & Creel, 2002; Pole et al., 2004). Apart from the presence of prey, prey selection may also be affected by the presence of larger competitors: the risk of encountering larger competitors increases with handling time of the kill, which is shorter for smaller prey items (Hamilton, 2002). However, compared to other ecosystems (presence larger competitors at kill sites 9–86%, kleptoparasitism 0–100%), kleptoparasitism and presence of larger competitors at kill sites of African wild dogs was not exceptionally high (Creel & Creel, 1998; van der Meer et al., 2011); therefore, interspecific competition alone does not seem to explain prey selection by the MPNP study packs.
Profitability of prey is related to energy content but also to energy spend finding, pursuing and subduing prey (Creel & Creel, 2002). Like in other ecosystems, along the MPNP floodplain impalas and baboons have formed interspecific associations to optimise feeding and anti-predator strategies (Davis & Ebersole, 2015). Consequently, search efficiency for impalas and baboons are likely to be similar; however, chase distance may differ substantially. When encountering a predator, impalas are quick to take flight, while baboons, when foraging on the ground during daytime, seek refuge in the nearest tree and when necessary confront a predator (Cowlishaw, 1997; Estes, 2004). The MPNP floodplain consists of open woodland with little understory in which it is relatively easy to detect approaching predators and difficult to find refuge. Such open habitat increases flight initiation distance (Stankowich & Blumstein, 2005) which increases the distance over which prey is chased by African wild dogs (Reich, 1981) and the likelihood of a kill (Creel & Creel, 2002). Where impalas are known for their manoeuvrability and high speed (ca. 50 km/h) when escaping predation (Wilson et al., 2018), baboons are much slower. In this study, baboons were always chased over short distances (<100 m) and, unlike impala hunts, baboon hunts would normally result in the pack outrunning and killing at least one individual in the troop before it found refuge. Such differences in hunting efficiency can outweigh a lower energy intake and enable African wild dogs to subsist on smaller prey species (Woodroffe et al., 2007).
As far as we are aware, this is the first study which describes preferential predation of African wild dogs on baboons (see also Cowlishaw, 1994; Hayward et al., 2006a). Hunting dangerous prey like baboons requires skills which vary among individuals (Jooste et al., 2013). Baboon hunting in MPNP is believed to have started with the original alpha female of pack I, which was first witnessed to hunt baboons about a decade ago (personal communication safari operators). Both study packs consist of offspring of this female. Although pack II initially avoided baboon predation, once seven dispersers of pack I joined the pack in December 2015, baboons became a preferred part of the diet. In addition to these two study packs, there are five known African wild dog packs in MPNP, only one of these other packs has ever been witnessed to predate on baboons (personal communication safari operators), this pack was formed mid 2017 and consists of four individuals of which two are dispersers from pack I. In accordance with Jooste et al. (2013), these observations suggest predation on baboons may be an individually acquired pattern of behaviour which disseminates through the MPNP African wild dog study packs via social learning (acquiring new behaviour by observing and imitating others, see Galef, 1976). However, further research will be necessary to confirm this hypothesis and to gain a more detailed insight in the various factors likely to affect the MPNP study packs’ unusual prey preference for baboons.
Corresponding author’s e-mail address: firstname.lastname@example.org
We would like to thank M. Hayward, G. Mills, D. Parker and an anonymous reviewer for critically reading the manuscript and suggesting substantial improvements. We thank the Research Council of Zimbabwe and the Zimbabwe Parks and Wildlife Management Authority for providing the necessary permits to carry out this research. We would like to express our gratitude to H. Madzikanda, F. Nsingo, N. Murray, H. Bandure, S. Josia, W. Sloss, B. Britton, J. Evans, R. Steinmann and M. Yates for their (logistic) support and assistance with the data collection. We also thank C. Sibanda, S. Phiri, G. Njamba and T. Tauro for their assistance with the faecal analyses.