Not all carnivores are big and dangerous to work with. Some are just furry little things with big ears, wandering around looking for termites and other insects to eat! And when these guys are habituated to the point that they allow humans to follow them around while they go about their nightly business, you have a recipe for the perfect behavioural data collection set-up! So let’s talk about bat-eared foxes (Otocyon megalotis) in the Kalahari, and how wind speed affects their foraging activities.
Let us start with the” batties” themselves, as they have affectionally been dubbed. These 30 cm tall carnivores sport exceptionally large ears (hence their name), weigh 3-4 kg and are myrmecophagous, meaning they predominantly feed on termites and ants. Their dentition is adapted to feeding on small invertebrate prey. Their carnassial sheer is not well developed, their teeth are quite small and a special adaption in their lower jaw allows them to perform a quick chomping action, killing insects before swallowing them. With between 46 and 50 teeth (and considerable individual variation), they have more teeth that any other living carnivore, or any heterodont placental mammal for that matter!
They occur in two geographically separated populations, one in Southern Africa (O. m. megalotis) and one in East Africa (O. m. virgatus), which reflects the gap in the distribution of their main prey, harvester termites. The two populations probably separated after the Pleistocene, when conditions became wetter and the harvester termites’ distribution changed.
Bat-eared foxes are mainly nocturnal and are often observed in pairs. They forage in more or less open grasslands, head titled downward, their large ears pointed to the ground, listening intently. Subterrain prey such as insects and other invertebrates, are located by the sounds they produce, and the foxes do not rely heavily on sight to find their food. Once located, they dig out their prey using their front paws, which they also use to excavate ants and their eggs from their nests. Termites are simply licked from the ground while they harvest vegetation material. If you would like to read more about bat-eared foxes and are looking for more information about them in Namibia, head over to our recently published book here: http://the-eis.com/elibrary/search/27193.
Now you understand why we got curious about how wind speed could affect bat-eared foxes
foraging behaviour, right? Since higher wind speeds produce stronger ambient noises that could potentially impair the capacity of foxes to locate their prey, we set out to answer that question. Our study site was located on the Kuruman River Reserve in South Africa’s Kalahari desert. Eighteen bat-eared foxes were habituated to allow humans following them on foot within a few meters, while they were foraging. Every night we went out for 2h walking with the foxes and recorded each item they ate, where and when. We then matched this feeding data with wind speed recorded on the reserve to test for any correlation. And well, we found very little… At the wind speeds recorded (0-15.5km/h), foraging behaviour seemed largely unaffected. Only in winter did we find an increased foraging rate with increasing wind speed, both outside and inside termite patches, not what we were expecting at all! We explain the absence of general effects by the fact that wind speeds during our observations were quite low. Since we observed bat-eared foxes stopping foraging during strong wind conditions preceding storms, we think that up to a threshold wind speed, foraging is unaffected and that above this threshold, foxes simply stop foraging, as their capacity to located prey would be too impaired make it worth the energy spent to continue foraging.
The positive effect of wind in winter is puzzling though… It might be due to the changes in activity patterns of foxes during this season. In winter, most insects, especially termites, become active during the day, as temperatures during the Kalahari nights are too low for them to keep foraging. As a result, bat-eared foxes also switch to a more diurnal activity. However, we observed that winter days were quite windy, especially in the mornings, with wind speed decreasing towards the end of the day. Since we mainly observed bat-eared foxes just after sunset, we suspect that in these windy winter days, they were compensating for missed foraging opportunities during the windiest parts of the day by increasing their foraging activity when the wind speed finally decreases.
The effects of anthropogenic noises (e.g. roads, airports) are starting to be well studied, particularly on birds, but much less is known about the impacts of natural sounds, like water and wind, on the behaviour of acoustic hunters, especially in mammals. Even if we found that bat-eared foxes are well adapted to the natural disturbance of moderate winds, it would be valuable to determine if the same holds true with higher wind speeds, or with other sources of noises. And as anthropogenic noise often disrupts natural soundscapes across a range of frequencies that differs from environmental and biological sources of sound, this acoustic adaptation may be severely tested with continuing global change.
You can find the full publication of your results here: https://link.springer.com/article/10.1007/s13364-023-00673-7