Half the Size, Yet Surprisingly Unafraid of Red Foxes: How Do Two Desert Foxes Coexist?
Body size often influences the outcome of competition among animals. Larger species may monopolize food, occupy preferred habitats or directly attack smaller competitors. In the Negev Desert of southern Israel, Rüppell's fox (Vulpes rueppellii) shares its habitat with just such a neighbour: the red fox (Vulpes vulpes). In this region, red foxes weigh about 3.5 kg on average, whereas Rüppell's foxes weigh only about 1.7 kg, making the red fox roughly twice as heavy. Under such circumstances, one might expect the smaller fox to become more vigilant in the presence of its larger competitor. Yet the actual pattern appears to be quite different.
The red fox is a highly adaptable, omnivorous member of the order Carnivora and readily exploits food associated with human activity. Studies from other regions have shown that red foxes can displace smaller fox species, take over their dens and even kill their young. Rüppell's fox, in contrast, is a desert-adapted species whose range partially overlaps that of the red fox in North Africa and the Arabian Peninsula. Tracking data from the Negev Desert suggest that the two species tend to favour different environments. Rüppell's foxes more often use flat terrain and creek bottoms, whereas red foxes are more closely associated with human settlements and higher elevations. Such spatial partitioning may reduce the frequency of direct encounters between them.
How vigilant, then, does a Rüppell's fox become when it detects a red fox nearby? And how does a red fox respond to another member of its own species? Researchers conducted 34 field trials within Rüppell's fox home ranges, each lasting two nights. Two feeding trays were placed 50 m apart, with six dead chicks buried in the sand at each tray as bait. Beside one tray, the researchers placed a stuffed red fox inside a mesh box trap, together with red fox faeces and the scent of red fox urine. The other tray served as a control and was accompanied by an identical but empty cage. Camera traps recorded the behaviour of foxes as they approached the food. The trials were carried out in 2017, 2018, 2022, 2023 and 2024, covering both the dry and wet seasons.
The recorded behaviours were divided into two broad categories. Eating, digging, walking slowly, standing in a nonalert posture, smelling and urinating were classified as relaxed behaviours. Fleeing, maintaining a posture suggesting readiness to escape, and showing rapid or jerky head movements associated with heightened vigilance were classified as stress-related behaviours. The researchers then compared the probability of a stress response and the amount of time the foxes spent at the feeding trays in the presence or absence of the simulated red fox.
During the dry season, the results were relatively uneventful. The presence of the stuffed red fox produced no significant difference in the probability of stress-related behaviour in either Rüppell's foxes or red foxes. During the wet season, however, the pattern changed. Both species were more likely to show stress responses at feeding trays with the simulated red fox, but the response was considerably stronger in red foxes themselves. The estimated probability of a stress response in red foxes facing the simulated conspecific was about 0.82, compared with only about 0.44 in Rüppell's foxes. At control trays without the simulated red fox, the estimates were very similar between species, at about 0.33 for red foxes and 0.31 for Rüppell's foxes. Red foxes therefore showed a stronger stress response to a conspecific than Rüppell's foxes showed to a red fox.
Season | Treatment | Probability of stress response in red foxes | Probability of stress response in Rüppell's foxes |
Wet season | Without simulated red fox | 0.33 | 0.31 |
Wet season | With simulated red fox | 0.82 | 0.44 |
Dry season | Without simulated red fox | Approx. 0.21-0.22 | Approx. 0.30 |
Dry season | With simulated red fox | Approx. 0.31 | Approx. 0.31 |
Why were red foxes especially sensitive to another red fox during the wet season? This period overlaps with their breeding season. Mating occurs mainly in January and February, followed by births in March. At this time of year, territories, mates and vulnerable pups may all be threatened by other members of the same species, potentially increasing the risks associated with an unfamiliar red fox entering the territory. The stuffed red fox used in the experiment may therefore have been perceived as a potential territorial intruder, triggering a stronger vigilance response.
Why, then, did Rüppell's foxes show relatively little fear of the simulated red fox? One possible explanation is that the two species rarely encounter one another directly under normal conditions. Rüppell's foxes and red foxes differ in their preferred habitats and food resources, and within the study area the probability of a Rüppell's fox encountering a red fox inside its home range may be relatively low. Long-term niche partitioning may therefore have reduced the frequency of direct conflict, limiting the development of a particularly strong vigilance response in Rüppell's foxes.
Rüppell's foxes diverged from red foxes approximately 576,000 years ago, while red foxes dispersed into North Africa around 78,000 years ago. Genetic introgression has also occurred between the two species. These findings suggest that red foxes and Rüppell's foxes have coexisted in North Africa and the Arabian deserts for a considerable period of time. As the two species increasingly came to use different habitats and food resources, the frequency of direct confrontation may have declined. A smaller Rüppell's fox living today may therefore have little reason to treat every nearby red fox as an immediate threat.
This long-standing coexistence could nevertheless be altered by human activity. Red foxes are particularly adept at exploiting resources associated with human settlements, agriculture and food waste. As these anthropogenic resources spread into relatively intact desert environments, they may allow red foxes to expand farther into arid habitats, increasing the overlap between the two species. Maintaining a heterogeneous desert landscape and reducing human food waste within core desert habitats may therefore help limit further red fox expansion and preserve the ecological conditions that currently allow these two fox species to coexist.
Author: Shui-Ye You
Reference:
Geffen E et al. (2026). Evolutionary history and seasonal dynamics shape interspecific interactions between two sympatric desert fox species. Animal Behaviour.
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