Interspecies teamwork: Evidence of interspecific foraging associations between Cape foxes and striped polecats in the southern Kalahari

Interspecific associations, defined as individuals of two species (or more) behaving as members of the same group, occur across a wide range of taxa including birds, fishes and mammals. Both or all individuals usually derive benefits from the association, whether that be foraging advantages, increased predator avoidance, or both (Stensland et al., 2003). Among mammals, several interspecific foraging associations involving two carnivores have been identified, but the best-known concerns American badgers (Taxidea taxus) and coyotes (Canis latrans) in the northern Hemisphere (Minta et al., 1992; Stensland et al., 2003; Thornton et al., 2018). Occasionally, swift foxes (Vulpes velox; Ausband & Ausband, 2006) or San Joaquin kit foxes (Vulpes macrotis mutica; Clark et al., 2015) were also observed associating with American badgers. When hunting burrowing animals such as ground squirrels (Spermophilus sp.), badgers dig and move below ground while coyotes chase prey above ground. When together, their hunting skills are complementary: if a squirrel is flushed to the surface by a badger, the coyote will pursue it; if a squirrel goes below ground because a coyote is standing guard outside, the badger can hunt it underground (Lehner, 1981; Minta et al., 1992). American badger-canid pairings may take on various forms. Some individuals form recurring associations, follow one another alternatively, rest, play and hunt together, sometimes displaying coordinated hunting techniques (called “double rush”; Cahalane, 1950; Lehner, 1981; Minta et al., 1992). Other pairs may be less interactive, with the canid trailing behind the badger and watching the latter digging in case an escaping prey emerges (Ausband & Ausband, 2006; Clark et al., 2015). Overall, Minta et al. (1992) described the American badger-coyote partnership as “a nonevolved mutualism that took the form of a short-term, two-species social system that benefited both.” Another example of such an association involves a similar pair of species, the honey badger (Mellivora capensis) and the black-backed jackal (Lupullela mesomelas) in the Kalahari, although their interactions are mainly described as kleptoparasitism rather than mutualism (Begg et al., 2022; Gorta, 2020). Here, we present evidence of interspecific associations between Cape foxes (Vulpes chama) and striped polecats (Ictonyx striatus) in the Kalahari region of South Africa. Observations of close interactions between Cape foxes and striped polecats were recorded in the lion-free Duneveld habitat of Tswalu Kalahari Reserve (27°13'S, 22°26' E), Northern Cape, South Africa (see Tokura et al., 2018 for more details). Both species are primarily nocturnal mammals native to sub-Saharan Africa, although they are sympatric only in southern Africa (Hoffmann, 2014; Stuart et al., 2015). The co-authors WP and AS made the most detailed observation, which was captured on a digital camera. In addition to observations by WP and AS, Tswalu field guides and researchers reported sightings involving the two species, including the approximate location, date, time of day, and behaviours. The observations by guides and researchers occurred both before and after the observations by WP and AS. A video from a camera trap deployed on the reserve that depicted both species together was also reported. Using the locations of sightings, we estimated the area encompassing all sightings using the Minimum Convex Polygon method in QGIS (version 3.16). We obtained 16 observations of a Cape fox and striped polecat pair (2015–2019), including three observations by WP and AS, 12 reports from seven observers and one report from camera trap footage, across an area spanning 95 km2 (Figure 1). The most detailed, made by WP and AS on foot, took place on 13 November 2016 between 20 h32 and 21 h26, from a distance of 30–50 m. The interaction involved a single Cape fox and a single striped polecat on a foraging expedition (Figure 2). Each individual interchangeably followed the other at a distance ranging from 1 to 15 m. When a small ground squirrel (Geosciurus inauris) or meerkat (Suricata suricatta) burrow system was located, the polecat entered the burrow. The Cape fox remained alert above ground, and then laid in wait next to the burrow system. While the polecat was underground, an unidentified rodent was flushed out of the burrow. The Cape fox captured the rodent with its mouth, but remained on site. Incidentally, a bat-eared fox (Otocyon megalotis) approached, and made an alarm call. The Cape fox dropped its prey, seemingly in response to the alarm call. The polecat retreated to the burrow system and displayed nervous behaviour by repeatedly shuttling in and out of the burrow. The Cape fox laid in wait until the polecat emerged, at which point the two ran off together once again. The Cape fox had its tail raised whenever the two were together. We could not see what happened to the prey item. On two other occasions, WP observed a Cape fox and polecat pair running together, but not engaged in hunting. The 13 additional observations were also of the two species running together, with no reports of prey being hunted or captured. Most sightings occurred between August and December (n = 12 of 14; two reports did not include day/month). All sightings occurred between 19 h00 and 03 h00. To our knowledge, this is the first report of an interspecific foraging association between these two small mammalian carnivores, which suggests that facilitative foraging may be more widespread among intraguild carnivores than previously believed. Like the badger-coyote interaction, a mustelid and a canid paired up to hunt ground-dwelling prey. Our detailed observation in November 2016 was strikingly similar to descriptions of badger-coyote interactions, including the way both individuals interchangeably followed one another, and waited for the other before departing, behaviours indicative of a willingness to maintain the association. Considering Cape fox home ranges are ~27 km2 (Kamler et al., 2012) and the area encompassing all sightings at Tswalu was ~95 km2, the interactions we observed may be from more than one Cape fox-polecat pair and could potentially involve three pairs. Most of the sightings were reported between August and December, during a time of the year (spring and summer) when rodents are scarce in South African grasslands (Avenant, 2011). Although Cape fox and polecat diets overlap, the former depends more on rodents as a primary food source (Kamler et al., 2012; Klare et al., 2014). It is possible that Cape foxes become more reliant on associations with polecats for food acquisition when the abundance of their primary food resources is at its lowest. Another explanation for the high reporting rate of sightings during spring and summer may relate to observer bias, since game drives occur at night during these seasons, while they end before or shortly after nightfall during colder months (pers. comms., Gus van Dyk, Tswalu Kalahari Reserve). To understand how common these associations are and what the drivers for such partnerships are requires more investigation. Striped polecats have a wide African distribution, including the Sahel zone of western and northern Africa, where another sympatric similar-sized fox species exists, such as the pale fox (Vulpes pallida). We hypothesise that, like the American badger-coyote association, the Cape fox-polecat association is a form of mutualism. While one or both species may benefit from increased food acquisition, the small polecat may also benefit from the wider-ranging prey/predator detection capacities of the fox. Determining the costs and benefits for each species will be crucial to confirm or refute this hypothesis but represents a challenging task, further complicated by the fact that human presence may directly influence such an interaction (Minta et al., 1992). However, the use of camera trapping surveys have been shown to be an effective way to detect these cryptic associations and link them with spatio-temporal environmental characteristics (Thornton et al., 2018). We hope that recognising that more interspecific carnivore pairings occur will help raise awareness in the field, encourage reporting of such observations, and instigate studies specifically aiming at understanding the drivers of these associations and quantifying their ecological implications. Ecosystems and food webs are complex, and the interactions we have recorded emphasise those complexities and the need to focus more attention on alternative interactions and not on interactions that fall traditionally within the competitive context. We thank Tswalu Kalahari Reserve and the Tswalu Foundation for hosting us during the time at which we made the observations reported in this paper. We also thank field guides and researchers Dylan Brandt, Francois Pienaar, Juan Venter, Kallie Moatlhodi, Liam Charlton, Roxanne Ungerer, and Rudi Venter for contributing valuable information about sightings of Cape foxes and polecats. The authors report no conflicts of interest. The data used to generate the sightings map, the additional data gathered for individual sightings, and the camera trap footage are available by request through the corresponding author.

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