Rock Monitoring Research Articles

The potential predators of pancake tortoises (Malacochersus tornieri) in Kenya

Studying the interactions between prey and predators is crucial for understanding the intricacies of predator-prey dynamics and for formulating effective conservation strategies. Yet there is almost no systematic analysis of pancake tortoise predation, and its consequences on the tortoise populations. Using camera trapping and visual encounter surveys, we recorded the animals visiting the crevices inhabited by pancake tortoises, as well as their surroundings. From our data, we propose which visitors were potential predators, and consider predator impacts on the species. We suggest ten species (21.3%) as potential predators, among the 47 visiting the tortoise crevices between July 2020 and November 2022. We encountered six adult pancake tortoises killed and eaten by unknown predators. Four of six eggs laid by pancake tortoises in May−June 2022 were also depredated. The white-tailed mongoose (Ichneumia albicauda) and the honey badger (Mellivora capensis) were recorded probing rock crevices inhabited by pancake tortoises, with their behaviour suggesting potential predation upon tortoises. We recorded the rock monitor lizard (Varanus albigularis) and common dwarf mongoose (Helogale parvula) digging pancake tortoise nest sites. This study significantly advances our understanding of the predation risk to the critically endangered pancake tortoise.

Body Size, Defensive Behaviour, and Season Influence Mortality Probability in Wildlife Interactions with Electrified Fences

Like many anthropogenic linear structures, fences are ubiquitous across South Africa and increasingly in the rest of Africa. Fences play a key role in conservation and livelihoods, including inter alia demarcating protected areas, safeguarding vulnerable populations of threatened species, and facilitating food security through the management of livestock and mitigating livestock predation from native predators. However, fences also have several deleterious effects, including curtailing historical animal migration routes, denying animals access to seasonally important resources, and providing a physical barrier on which animals can become entangled or electrocuted. Despite these negative effects being commonly known, few African studies have quantified the threat specifically posed by electrified fences, although several studies have highlighted the risks posed by unelectrified fences. This study investigated vertebrate interactions along 108 km of electrified fencing on a private game farm over nearly five years and analysed the effect of several predictive variables on the outcome of interactions with fencing. Overall, 43 vertebrate species were recorded interacting with the fencing on 782 occasions, resulting in 213 fatal interactions. Medium-sized mammals, specifically steenbok (Raphicerus campestris ) and Temminck's pangolin (Smutsia temminckii ), and large reptiles including rock monitor (Varanus albigularis ) and serrated tent tortoise (Psammobates oculifer ) were particularly prone to fatal interactions. Body size, season and defensive behaviour were the best predictors of a species' tendency for fatal interactions with electrified fencing. This study records several additional species that have not previously been recorded interacting with electrified fencing, and for the first time highlights the potentially large, albeit possibly local, negative effect that electrified fencing has on the rock monitor.

A new species of Oochoristica (Cyclophyllidea, Anoplocephalidae) from Varanus albigularis (Squamata, Varanidae) in Kenya

Oochoristica varanicola sp. nov. (Anoplocephalidae, Linstowiinae) is described from Varanus albigularis in Kenya. It is the third species of this cestode genus described from monitor lizards. Oochoristica varanicola differs from other species from Varanus, as well as from the numerous other species in the genus by a unique combination of characters that include a high number of testes (92–134) and a long cirrus-sac (225–290 × 63–90 µm). Both the host and the locality are new records for the genus Oochoristica.

Amendment of Rostellotaenia Freze, 1963 (Cestoda: Proteocephalidae) from African monitors (Varanus spp.) and a redescription of its type-species, R. nilotica (Beddard, 1913).

Based on morphological evaluation of type-specimens and new material collected in three species of monitor lizards (Squamata: Varanidae), the diagnosis of the monotypic Rostellotaenia Freze, 1963 (Proteocephalidae: 'Acanthotaeniinae') is amended. The genus differs from Acanthotaenia von Linstow, 1903, with which it was previously synonymised, by the shape of the scolex with a wide, dome-shaped rostellum, the posterior extent of the uterus, which does not overpass the ovarian isthmus posteriorly, well-developed retractor muscles connecting the rostellum with the neck region, absence of a well-developed, ring-like vaginal sphincter, shorter and wider proglottides, and geographical distribution (Ethiopian region only). The type- and only species, R. nilotica (Beddard, 1913), is redescribed and two new definitive hosts, Varanus albigularis Daudin and V. exanthematicus (Bosc), are reported. Host specificity of R. nilotica, which exhibits remarkable morphological variability, is stenoxenous, i.e. it occurs in several congeneric species of African monitor lizards, unlike species of Acanthotaenia, which are strictly specific (oioxenous).

Conserved sex chromosomes and karyotype evolution in monitor lizards (Varanidae).

Despite their long history with the basal split dating back to the Eocene, all species of monitor lizards (family Varanidae) studied so far share the same chromosome number of 2n = 40. However, there are differences in the morphology of the macrochromosome pairs 5-8. Further, sex determination, which revealed ZZ/ZW sex microchromosomes, was studied only in a few varanid species and only with techniques that did not test their homology. The aim of this study was to (i) test if cryptic interchromosomal rearrangements of larger chromosomal blocks occurred during the karyotype evolution of this group, (ii) contribute to the reconstruction of the varanid ancestral karyotype, and (iii) test homology of sex chromosomes among varanids. We investigated these issues by hybridizing flow sorted chromosome paints from Varanus komodoensis to metaphases of nine species of monitor lizards. The results show that differences in the morphology of the chromosome pairs 5-8 can be attributed to intrachromosomal rearrangements, which led to transitions between acrocentric and metacentric chromosomes in both directions. We also documented the first case of spontaneous triploidy among varanids in Varanus albigularis. The triploid individual was fully grown, which demonstrates that polyploidization is compatible with life in this lineage. We found that the W chromosome differs between species in size and heterochromatin content. The varanid Z chromosome is clearly conserved in all the analyzed species. Varanids, in addition to iguanas, caenophidian snakes, and lacertid lizards, are another squamate group with highly conserved sex chromosomes over a long evolutionary time.

Acanthocephalans, Including the Description of a New Species of Mediorhynchus (Gigantorhynchidae) and a Redescription of Centrorhynchus clitorideus (Centrorhynchidae) from Vertebrate Hosts from South Africa

Forty-seven individuals comprising 4 species of birds, Tockus leucomelas, Crecopsis egregia, Turdus smithi, and Bubo africanus; 4 species of mammals, Otolemur crassicaudatus, Gerbilliscus leucogaster, Mus minutoides, and Mus sp.; and 1 species of reptile, Varanus albigularis, all from South Africa were examined for acanthocephalans. Centrorhynchus clitorideus, Mediorhynchus mokgalongi n. sp., Masticophis taeniatus, Moniliformis acomysi, Moniliformis sp., Plagiorhynchus (Prosthorhynchus) cylindraceus, and a putative new genus of the Oligacanthorhynchidae were found. Additional characters of C. clitorideus were described. The new species of Mediorhynchus differs from all congeners by a suite of characters, including a proboscis armature of 125–156 hooks arranged in 24–26 longitudinal rows of 24–26 hooks and 30 rows of 5–6 spines. The putative new genus has a total of 24 hooks arranged in 12 longitudinal rows of 2 hooks. All are new host and locality records.

A Comparative Analysis of the Diets ofVaranusalbigularisandVaranus niloticusin South Africa

We present data from gut content analyses of Varanus albigularis (savanna monitor) and V. niloticus (water monitor) in South Africa. Both species are generalist, opportunistic feeders. We did not detect any sex-based differences in the diet of V. albigularis, and there were relatively high levels of dietary overlap between the species, although there were significant differences for certain prey types. These differences match differences in habitat use between the species: the more aquatic V. niloticus consumed aquatic prey, such as amphibians and crabs, more often than did V. albigularis. Varanus albigularis included more terrestrial prey such as diplopods in its diet. Tortoises and millipedes were also prominent in the V. albigularis diet, constituting an important component of dietary intake. Few of our samples from V. albigularis had empty stomachs, suggesting that this species may occupy a lower trophic level than its Australian counterparts. Although there is a large degree of overlap in the diets of the two species, there is a trend for V. albigularis to eat more slow-moving prey. These differences result in the species foraging at different trophic levels.

A comparative analysis of the diets of Varanus albigularis and Varanus niloticus in South Africa

We present data from gut content analyses of Varanus albigularis (savanna monitor) and V. niloticus (water monitor) in South Africa. Both species are generalist, opportunistic feeders. We did not detect any sex-based differences in the diet of V. albigularis, and there were relatively high levels of dietary overlap between the species, although there were significant differences for certain prey types. These differences match differences in habitat use between the species: the more aquatic V. niloticus consumed aquatic prey, such as amphibians and crabs, more often than did V. albigularis. Varanus albigularis included more terrestrial prey such as diplopods in its diet. Tortoises and millipedes were also prominent in the V. albigularis diet, constituting an important component of dietary intake. Few of our samples from V. albigularis had empty stomachs, suggesting that this species may occupy a lower trophic level than its Australian counterparts. Although there is a large degree of overlap in the diets of the two species, there is a trend for V. albigularis to eat more slow-moving prey. These differences result in the species foraging at different trophic levels.

Yolk coelomitis in a white-throated monitor lizard (Varanus albigularis) : short communication

Yolk coelomitis as a result of pre-ovulatory follicular stasis is a common disorder in captive reptiles, especially in captive lizards of various genera. The clinical signs are generally fairly non-specific and diagnosis is based on clinical signs together with most of the common diagnostic modalities. The condition is most likely a husbandry and environment-related reproductive disorder. It has not been reported in wild free-living specimens. This report describes the clinical presentation and post mortem lesions in a white-throated monitor lizard that died during treatment for non-specific clinical signs related to a severe yolk coelomitis.

Restoring Vitamin D in Monitor Lizards: Exploring the Efficacy of Dietary and UVB Sources

ABSTRACT We studied the effects of ultraviolet B (UVB) exposure or administration of dietary vitamin D3 on serum vitamin D3, serum 25-hydroxyvitamin D3 (25[OH]D), calcium, and phosphorus in juvenile black-throated monitor lizards (Varanus albigularis) deprived of all sources of vitamin D for 87 days. Deprivation resulted in significant decreases of circulating levels of 25(OH)D (25–35%), vitamin D3 (73–76%), calcium (6%), and phosphorus (16%). The half-life of circulating 25(OH)D during deprivation was estimated to be from 128–139 days. After deprivation, eight monitors were given a single dose of UVB from exposure for 10–20 minutes to a Spectroline UVB lamp. The dose resulted in an average of 14.2% conversion of provitamin D3 to previtamin D3 and photoproducts within in vitro models. When administered once every week for 92 days, the dose failed to significantly modify the decline of serum 25(OH)D; however, the decline of vitamin D3 seemed to level off. The overall effect of the UVB dosing was weak, and ...

Rapid solving of a problem apparatus by juvenile black-throated monitor lizards (Varanus albigularis albigularis)

It is widely accepted that providing stimulus enrichment is an important part of the development and maintenance of behavior and well-being in mammals. However, extending this idea to non-avian reptiles has barely been explored, certainly as an aid to cognitive development. Monitor lizards have a reputation for being highly curious and intelligent lizards, but quantitative experiments are necessary to evaluate such impressions as well as the value of providing enrichment to captive squamate reptiles. In this study eight juvenile black-throated monitors, Varanus albigularis, were tested in their home enclosures with three presentations, at weekly intervals, of a novel task apparatus: a transparent food tube containing several prey. The food tube allowed the monitors to obtain prey by using hinged doors at either end of the tube to access food. All eight lizards learned to open the tube, insert head, and capture the prey within 10 min in the first trial. By the second trial, both mean latencies to access the tube and capture the first prey item decreased significantly, as did the use of ineffective responses such as shaking the tube. A further slight decrease occurred in the third trial. Due to the results of this and similar studies, serious consideration should be given to further testing of cognitive abilities in squamate reptiles. Incorporating problem solving tasks may also be useful to increase the activity level and captive well-being of squamate reptiles, especially monitor lizards.

Reproductive Biology of the White-Throated Savanna Monitor, Varanus albigularis

The reproductive biology of the white-throated savanna monitor lizard, Varanus albigularis, was examined in the arid savanna of Etosha National Park, Namibia. Both sexes were solitary during the the hot/wet season when prey were abundant, and during the hot/dry season when prey populations were declining. Male-male and male-female behavioral interactions were confined to a 2-3 week period at the transition from the cool/dry to the hot/dry seasons when prey populations were depleted. Interactions oc- curred at locations occupied by estrus females. Male-male interactions were restricted to resident males chasing intruding males after visual contact Males appeared to initially locate the general area occupied by females through scent cues. Once in visual contact with females, males exhibited a spasmodic body shudder, after which females responded by flattening their bodies. Mating generally occurred in trees. No aggression was noted between pairs during courtship or mating. At peak estrus, females had elevated (100 to 500-fold increase over non-reproductive period) plasma testosterone and total estrogen titers. Males showed similar dramatic increases in plasma testosterone levels during the mating period. Aspects of the reproductive biology of this species are discussed in the context of general patterns for the family Varanidae. As a group monitor lizards appear to be very conservative in the length of gestation, but highly variable in length of incubation. Length of incubation appears to be variably timed in order to place hatching during the period of greatest abundance of invertebrate prey.

Specific Dynamic Action of a Large Carnivorous Lizard, Varanus albigularis

Varanus albigularis inhabits grasslands of southern and eastern Africa and experiences months of fasting during the dry season (May–December) followed by voracious feeding during the wet season (January–April). Previous studies have found that sit-and-wait foraging snakes, which also experience long intervals between large meals, exhibit unprecedented increases in post-feeding metabolism, which reflects the added cost of up-regulating a previously quiescent gut and digesting a large meal. Hence we measured pre- and post-prandial oxygen consumption rates (V̇O 2) of adult V. albigularis in order to observe whether they exhibit similarly large metabolic responses to digestion as sit-and-wait foraging snakes. Following the consumption of meals consisting of ground turkey and snails, hard-boiled eggs, or juvenile rats, lizards rapidly increased their V̇O 2 to peak within 24–27 hr at 7–10 times pre-feeding values (mean = 0.035 mL O 2 · g −1 · h −1). During the 60–90 hr of significantly elevated V̇O 2, the extra oxygen consumed (the specific dynamic action) represented an energy expenditure of 830–1260 kJ. For meals that were fully digested, specific dynamic action equalled 24% of ingested energy. The magnitudes of V. albigularis post-prandial metabolic responses are similar to those previously observed for sit-and-wait foraging snakes. Like sit-and-wait foraging snakes, V. albigularis may also down-regulate intestinal performance during their months of fasting (suggested by their relatively low standard metabolic rate) and then up-regulate their gut (bearing its high energetic cost) upon feeding.

Sensory cues and foraging decisions in a large carnivorous lizard, Varanus albigularis

The white-throated savanna monitor, Varanus albigularis, is a large (>5 kg) carnivorous lizard that inhabits the arid savanna in southern Africa. In the natural environment, feeding occurs only during the 4-month wet season when invertebrate and small vertebrate prey are abundant. Seven experiments were conducted to examine the foraging, feeding and sensory discrimination behaviour of these lizards towards land snails, a favoured natural prey. Subjects were 16 subadult, captive-hatched lizards. Each lizard received several trials in choice discrimination tests with two or three types of snail stimuli differing in visual, chemical or tactile cues. Lizards differentiated between land snails using both visual and chemical cues. Large snails and those requiring short handling times were chosen over small snails and those requiring greater handling time. Neither snail movement nor snail weight were significant cues in choice of individual prey. Lizards preferred empty shells with fresh snail odour to empty snail shells without odour. The results suggest that these monitor lizards discriminate between prey items using visual and chemical cues. A result of their selectivity is obtaining a high caloric reward at a minimum energetic cost.

Treatment of Chronic Coxofemoral Luxation by Femoral Head and Neck Excision Arthroplasty in a White Throated Monitor, Varanus albigularis.

Treatment of Chronic Coxofemoral Luxation by Femoral Head and Neck Excision Arthroplasty in a White Throated Monitor, Varanus albigularis.

Movement Patterns and Density of Varanus albigularis

-A population of white-throated savanna monitor lizards (Varanus albigularis) in Etosha National Park, Namibia, was studied for 17 months. A total of 238 lizards was examined, of which 31 were radiotagged for periods up to 14 months. The hot/wet season (January-April) home ranges determined from radiotelemetry data were large and differed significantly between adult males (18.3 + 2.4 km2) and females (6.1 + 0.6 km2). During the cool/dry season (May-August) males and females utilized less than 10% of their wet season home range, except during the mating period (July-August), when males moved extensively while locating estrous females. When supplemental food was made available during the cool/ dry season, male lizards increased their daily movements over 30-fold, suggesting that food, not seasonal differences in ambient temperature, limits activity. The largest adult lizards were males; however, there was no difference in wet season mass between males and females of similar snout-vent length. The apparent sex ratio varied dramatically by season, but this was a result of the different activity patterns between the sexes. Overall, the data suggest parity between the sexes. The biomass of V. albigularis at least rivaled that of any sympatric medium and large-sized mammalian carnivore species in the park. Estimates of the biomass of lizard populations have concentrated on species that are physically small (e.g., Bennett and Gorman, 1979; Dunham, 1982; Ruby and Dunham, 1984; Pilorge, 1987; Barbault and Mou, 1988). Biomass estimates for populations of large lizards are far less common; however, several studies concerned with population estimates of large herbivorous lizards (Sauromalus, Cyclura) suggested that their density is often comparable to that of 407 This content downloaded from 157.55.39.124 on Sat, 23 Jul 2016 05:23:35 UTC All use subject to http://about.jstor.org/terms

Density-dependent foraging strategy of a large carnivorous lizard, the savanna monitor (Varanus albigularis).

Density-dependent foraging strategy of a large carnivorous lizard, the savanna monitor (Varanus albigularis).

Density-dependent foraging strategy of a large carnivorous lizard, the savanna monitor (Varanus albigularis).

Density-dependent foraging strategy of a large carnivorous lizard, the savanna monitor (Varanus albigularis).

Influence of temperature and moisture on eggs and embryos of the white-throated Savanna monitor Varanus albigularis: Implications for conservation

Eggs of the white-throated savanna monitor Varanus albigularis were incubated on vermiculite substrates at each of three temperatures (27, 29, 31°C) and moisture regimes (−150, −550, −1100kPa) in a factorial experiment to assess the effects of these variables on embryonic development. Hatching success was high in all treatments, so the chosen conditions did not drastically affect viability of embryos. Net absorption of water, duration of incubation by embryos, and size of hatchlings were positively correlated with moisture content of the substrate and negatively correlated with ambient temperature. Duration of incubation and size of hatchlings were similar for artificially and naturally incubated eggs, but hatching success of eggs in natural nests was only about half that of artificially-incubated eggs. Results from this study indicate that variations in moisture and temperature probably cause ecologically significant variation of physical characteristics in hatchling monitor lizards.

Naive ophiophagus lizards recognize and avoid venomous snakes using chemical cues

Monitor lizards prey on snakes. Conversely, venomous snakes prey on juvenile monitor lizards. Immediately after hatching, monitor lizards are naive to all prey items, thus correct assessment of snake prey is paramount for survival. Experiments were conducted to determine how hatchling monitor lizards (Varanus albigularis) with no previous exposure to snakes reacted to sympatric venomous and nonvenomous snakes. Hatchling lizards attacked harmless snakes, but avoided venomous species. Lizards readily accepted meat from skinned snakes, regardless of species. When invertebrate prey covered with skin segments from venomous snakes were restrained from moving, they were usually investigated by tongue-flicking and rejected. Unrestrained skin-covered prey, however, were generally attacked and eaten without prior evaluation by tongue-flicking. Attack was inhibited in trials in which unrestrained prey were tongue-flicked, suggesting that chemical cues contained in snake skins mediate avoidance of venomous snakes. Selection for the ability to perceive snake integumental chemicals may be especially strong in species that both consume and are consumed by snakes.