Inconspicuous, secretive, or sparsely distributed species receive relatively little research attention, potentially leading to uncertainty about their status and lack of efforts to conserve them. Karoo dwarf tortoises (Chersobius boulengeri) are endemic to South Africa, spend most of the time in retreats at remote arid locations, and are seldom seen. We conducted a 3‐year (2018–2020) mark‐recapture study to investigate the size and structure of the only Karoo dwarf tortoise population currently known to exist. The population in the 16‐ha core of our study site consisted primarily of adult males and females, at a density of 3.3 individuals/ha. Many individuals had severely worn shells and appeared old. Small individuals (straight carapace length <65 mm) represented just 8% of the population and were mostly recent hatchlings. Overall, tortoises had high estimated survival rates (0.77–0.95; lower 95% confidence limit for the smallest tortoises was 0.16), despite a 15‐month drought. The lack of small individuals may reflect low levels of recruitment and population decline. Predation by corvids was an obvious threat to all size classes. We estimated that the local population across the 250‐ha study area was 800–900 males and females, and recommend precautionary conservation measures focused on reducing human‐subsidized avian predation.
The availability of suitable refuges to buffer temperature extremes may be a critical determinant in the distribution of arid-zone ectotherms. We studied refuge selection of Kalahari tent tortoises over five seasons in two vegetation types to assess how seasonal climate change, vegetation type, and the size difference between sexes influence refuge selection. Plant refuges accounted for 78% and mammal burrows for 22% of refuges used. Burrow use did not differ between vegetation types or sexes but its use increased exponentially with maximum temperature, indicating that mammal burrows may be an essential resource to protect small-bodied tortoises against summer heat. Kalahari tent tortoises preferred grass refuges to other growth forms, whether shrubs or grasses were dominant in the habitat. Tall grass was selected in excess of availability, by males and females in both vegetation types, probably because it was denser than short grass and provided better protection against heat and predators. The increased use of short grass refuges in colder months may be linked to thermal needs because this growth form allowed P. oculifer to bask in filtered sunlight whilst being in cover. Females made greater use than males did of short grass refuges, perhaps because their larger size necessitated longer exposure to sunlight. Body size differences also explain why males required wider and denser refuges than females did to protect them against environmental hazards. Our results underscore the complexities of refuge selection by an arid-zone ectotherm and the role it may play in their distribution.
This communication presents observations of predatory and non-predatory encounters between white sharks and Cape fur seals in a shallow (3-6 m) channel between Geyser Rock and Dyer Island, South Africa. Within the channel Cape fur seals raft extensively for thermo-regulatory purposes, to play, or due to terrestrial competition for space. The channel's physical environment effectively limits a white shark's approach orientation to the horizontal plane, thus inhibiting it to effectively utilize depth, and associated stealth, to capture pinnipeds. In the absence of effective camouflage, sharks may patrol this area in search of unaware, incapacitated or dead seals. Here, predator mobbing is a behavioural strategy adopted by Cape fur seals to lower predation risk. Specific benefits of mobbing may include: (a) perception advertisement to sharks; (b) intra-specific communication of a shark's locality; (c) driving the shark away from the area; (d) increased vigilance; (e) advertisement of a mobber's good health to a shark; and (f) possibly learning about a predator's behavioural capabilities by inexperienced prey. Mobbing expression is further promoted by the channel's shallow nature which enhances a seal's ability to visually detect the shark, and therefore makes it easier for a seal to evade it (reducing immediate predation risk). This environment thus promotes the widespread use of mobbing amongst Cape fur seals when confronted with a patrolling white shark.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.