Parental defence on the reef: antipredator tactics of coral‐reef fishes against egg‐eating seasnakes

On coral reefs in New Caledonia, the eggs of demersal‐spawning fishes are consumed by turtle‐headed seasnakes (Emydocephalus annulatus). Fish repel nest‐raiding snakes by a series of tactics. We recorded 232 cases (involving 22 fish species) of antipredator behaviour towards snakes on a reef near Noumea. Blennies and gobies focused their attacks on snakes entering their nests, whereas damselfish (Pomacentridae) attacked passing snakes, as well as nest‐raiders (reflecting territorial defence). Biting the snake was the most common form of attack, although damselfish and blennies also slapped snakes with the tail, or (blennies only) plugged the nest entrance with the parent fish's body. Gobies rarely defended the nest, although they sometimes bit or threw sand at the snake. A snake was more likely to flee if it was attacked before it began feeding rather than after it found the eggs (82% versus 3% repelled) and if bitten on the head rather than the body (68% versus 53%). Tail‐slaps were not effective, although plugging the burrow and throwing sand often caused snakes to flee. These strong patterns reflect phylogenetic variation in fish behaviour (e.g. damselfish detect a snake approach sooner than do substrate‐dwelling blennies and gobies) coupled with intraspecific variation in snake diets. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 415–425.     

Rhesus Macaques (Macaca mulatta) Use Posture to Assess Level of Threat From Snakes

Once prey animals have detected predators, they must make decisions about how to respond based on a cost‐benefit analysis of their risk level. The threat sensitivity hypothesis predicts that prey animals match their response to the level of risk, with high‐risk predator encounters eliciting stronger evasive responses than low‐risk encounters. Primates are known prey of snakes, yet they vary their responses toward snakes. We predicted that primates match their response to the threat level from snakes by assessing posture, with striking postures indicating greater risk than coiled postures and coiled postures indicating greater risk than extended sinusoidal postures. We tested this prediction in a series of experimental trials in which captive rhesus macaques (Macaca mulatta) were exposed to snake models in those postures. Results supported the predictions: macaques responded more strongly to a snake model in a striking posture than in a coiled posture and more to a snake model in a coiled posture than to an extended sinusoidal snake model. We also examined responses of macaques to a partially exposed snake model to mimic the condition of incomplete information, as snakes are often occluded by vegetation. The occluded snake model evoked a response comparable to that of the striking snake. These findings support the threat sensitivity hypothesis. Rhesus macaques use the posture of snakes as a cue in threat assessment, responding more intensely as threat increases, and they also behave as if risk is elevated when their information about snakes is incomplete.     

Effects of season, sex and body size on the feeding ecology of turtle-headed sea snakes (Emydocephalus annulatus) on IndoPacific inshore coral reefs

In terrestrial snakes, many cases of intraspecific shifts in dietary habits as a function of predator sex and body size are driven by gape limitation and hence are most common in species that feed on relatively large prey and exhibit a wide body-size range. Our data on sea snakes reveal an alternative mechanism for intraspecific niche partitioning, based on sex-specific seasonal anorexia induced by reproductive activities. Turtle-headed sea snakes (Emydocephalus annulatus) on coral reefs in the New Caledonian Lagoon feed entirely on the eggs of demersal-spawning fishes. DNA sequence data (cytochrome b gene) on eggs that we palpated from stomachs of 37 snakes showed that despite this ontogenetic stage specialization, the prey comes from a taxonomically diverse array of species including damselfish (41 % of samples, at least 5 species), blennies (41 %, 4 species) and gobies (19 %, 5 species). The composition of snake diets shifted seasonally (with damselfish dominating in winter but not summer), presumably reflecting seasonality of fish reproduction. That seasonal shift affects male and female snakes differently, because reproduction is incompatible with foraging. Adult female sea snakes ceased feeding when they became heavily distended with developing embryos in late summer, and males ceased feeding while they were mate searching in winter. The sex divergence in foraging habits may be amplified by sexual size dimorphism; females grow larger than males, and larger snakes (of both sexes) feed more on damselfish (which often lay their eggs in exposed sites) than on blennies and gobies (whose eggs are hidden within narrow crevices). Specific features of reproductive biology of coral reef fish (seasonality and nest type) have generated intraspecific niche partitioning in these sea snakes, by mechanisms different from those that apply to terrestrial snakes.     

Perceived predation risk as a function of predator dietary cues in terrestrial salamanders

Prey often avoid predator chemical cues, and in aquatic systems, prey may even appraise predation risk via cues associated with the predator's diet. However, this relationship has not been shown for terrestrial predator-prey systems, where the proximity of predators and prey, and the intensity of predator chemical cues in the environment, may be less than in aquatic systems. In the laboratory, we tested behavioural responses (avoidance, habituation and activity) of terrestrial red-backed salamanders, Plethodon cinereus, to chemical cues from garter snakes, Thamnophis sirtalis, fed either red-backed salamanders or earthworms (Lumbricus spp.). We placed salamanders in arenas lined with paper towels pretreated with snake chemicals, and monitored salamander movements during 120 min. Salamanders avoided substrates preconditioned by earthworm-fed (avoidanceX+/-SE=91.1+/-2.5%, N=25) and salamander-fed (95.2+/-2.5%, N=25) snakes, when tested against untreated substrate (control). Salamanders avoided cues from salamander-fed snakes more strongly (75.2+/-5.5%, N=25) than earthworm-fed snakes when subjected to both treatments simultaneously, implying that salamanders were sensitive to predator diet. Salamanders tended to avoid snake substrate more strongly during the last 60 min of a trial, but activity patterns were similar between salamanders exposed exclusively to control substrate versus those subject to snake cues. In another experiment, salamanders failed to avoid cues from dead conspecifics, suggesting that the stronger avoidance of salamander-fed snakes in the previous experiment was not directly due to chemical cues emitted by predator-killed salamanders. Salamanders also did not discriminate between cues from a salamander-fed snake versus a salamander-fed snake that was recently switched (i.e. <14 days) to an earthworm diet. Our results imply that terrestrial salamanders are sensitive to perceived predation risk via by-products of predator diet, and that snake predators rather than dead salamanders may be largely responsible for the release of such chemicals. Copyright 1999 The Association for the Study of Animal Behaviour.     

Are Diet Preferences Associated to Skulls Shape Diversification in Xenodontine Snakes?

Snakes are a highly successful group of vertebrates, within great diversity in habitat, diet, and morphology. The unique adaptations for the snake skull for ingesting large prey in more primitive macrostomatan snakes have been well documented. However, subsequent diversification in snake cranial shape in relation to dietary specializations has rarely been studied (e.g. piscivory in natricine snakes). Here we examine a large clade of snakes with a broad spectrum of diet preferences to test if diet preferences are correlated to shape variation in snake skulls. Specifically, we studied the Xenodontinae snakes, a speciose clade of South American snakes, which show a broad range of diets including invertebrates, amphibians, snakes, lizards, and small mammals. We characterized the skull morphology of 19 species of xenodontine snakes using geometric morphometric techniques, and used phylogenetic comparative methods to test the association between diet and skull morphology. Using phylogenetic partial least squares analysis (PPLS) we show that skull morphology is highly associated with diet preferences in xenodontine snakes.     

Seasonal variation in terrestrial resource subsidies influences trophic niche width and overlap in two aquatic snake species: a stable isotope approach

Quantifying diet is essential for understanding the functional role of species with regard to energy processing, transfer, and storage within ecosystems. Recently, variance structure in the stable isotope composition of consumer tissues has been touted as a robust tool for quantifying trophic niche width, a task that has previously proven difficult due to bias in direct dietary analyses and difficulties in integrating diet composition over time. We used carbon and nitrogen stable isotope analyses to examine trophic niche width of two sympatric aquatic snakes, banded watersnakes Nerodia fasciata and black swamp snakes Seminatrix pygaea inhabiting an isolated wetland where seasonal migrations of amphibian prey cause dramatic shifts in resource availability. Specifically, we characterized snake and prey isotope compositions through time, space, and ontogeny and examined isotope values in relation to prey availability and snake diets assessed by gut content analysis. We determined that prey cluster into functional groups based on similarity of isotopic composition and seasonal availability. Isotope variance structure indicated that the trophic niche width of the banded watersnake was broader (more generalist) than that of the black swamp snake. Banded watersnakes also exhibited seasonal variation in isotope composition, suggesting seasonal diet shifts that track amphibian prey availability. Conversely, black swamp snakes exhibited little seasonal variation but displayed strong ontogenetic shifts in carbon and nitrogen isotope composition that closely paralleled ontogenetic shifts in their primary prey, paedomorphic mole salamanders Ambystoma talpoideum. Although niche dimensions are often treated as static, our results demonstrate that seasonal shifts in niche dimensions can lead to changes in niche overlap between sympatric species. Such short‐term fluctuations in niche overlap can influence competitive interactions and consequently the composition and dynamics of communities and ecosystems.     

Convergence in trophic morphology and feeding performance among piscivorous natricine snakes

Piscivory has independently evolved numerous times amongst snakes, and therefore these animals provide a powerful opportunity to test for convergent evolution in a vertebrate feeding system. In this study, we integrate performance trials with comparative methods to test the hypothesis that piscivory drives convergence in trophic morphology and feeding performance among natricine snakes. Within and across species, increasing the relative length of the quadrate bone in the skull is positively and strongly linked to a reduction in the time needed to swallow large fish prey. Thus, our feeding experiments suggest that a longer quadrate bone enables snakes to better conform their head shape to the shape of the prey during swallowing. Ancestral diet reconstructions and phylogenetically corrected multiple regression analyses further reveal that evolutionary increases in piscivory are coupled to the evolution of relatively longer quadrates, and hence improved feeding performance on fish prey in these animals. The exploitation of similar dietary niches drives the evolution of convergent trophic morphologies and feeding performances in natricine snakes.     

Trophic divergence despite morphological convergence in a continental radiation of snakes

Ecological and phenotypic convergence is a potential outcome of adaptive radiation in response to ecological opportunity. However, a number of factors may limit convergence during evolutionary radiations, including interregional differences in biogeographic history and clade-specific constraints on form and function. Here, we demonstrate that a single clade of terrestrial snakes from Australia—the oxyuranine elapids—exhibits widespread morphological convergence with a phylogenetically diverse and distantly related assemblage of snakes from North America. Australian elapids have evolved nearly the full spectrum of phenotypic modalities that occurs among North American snakes. Much of the convergence appears to involve the recurrent evolution of stereotyped morphologies associated with foraging mode, locomotion and habitat use. By contrast, analysis of snake diets indicates striking divergence in feeding ecology between these faunas, partially reflecting regional differences in ecological allometry between Australia and North America. Widespread phenotypic convergence with the North American snake fauna coupled with divergence in feeding ecology are clear examples of how independent continental radiations may converge along some ecological axes yet differ profoundly along others.     

Snake diets and the deep history hypothesis

The structure of animal communities has long been of interest to ecologists. Two different hypotheses have been proposed to explain origins of ecological differences among species within present‐day communities. The competition–predation hypothesis states that species interactions drive the evolution of divergence in resource use and niche characteristics. This hypothesis predicts that ecological traits of coexisting species are independent of phylogeny and result from relatively recent species interactions. The deep history hypothesis suggests that divergences deep in the evolutionary history of organisms resulted in niche preferences that are maintained, for the most part, in species represented in present‐day assemblages. Consequently, ecological traits of coexisting species can be predicted based on phylogeny regardless of the community in which individual species presently reside. In the present study, we test the deep history hypothesis along one niche axis, diet, using snakes as our model clade of organisms. Almost 70% of the variation in snake diets is associated with seven major divergences in snake evolutionary history. We discuss these results in the light of relevant morphological, behavioural, and ecological correlates of dietary shifts in snakes. We also discuss the implications of our results with respect to the deep history hypothesis. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 476–486.     

Postprandial responses in the African rhombig egg eater (Dasypeltis scabra)

The African rhombic egg eater (Dasypeltis scabra) is a colubrid snake feeding exclusively on bird eggs. Frequency of feeding is governed by the seasonal availability of bird eggs; i.e., long fasting intervals change with relatively short periods when plenty of food is available. Intermittent feeding snakes show a remarkable postprandial increase of metabolic rate and digestive organ size. The postprandial increase in metabolic rate (specific dynamic action, SDA) in snakes is affected by meal size, temperature, and meal composition. A major portion of SDA in snakes is allocated to gastric function and the breakdown of the meal. We hypothesize that SDA in egg eaters is lower than in other snake species, because egg eaters feed on “liquid” food that does not require enzymatic breakdown in the stomach. We also hypothesized that other components of the postprandial response of egg eaters (e.g., size changes of the intestine and the liver) do not differ from other snakes. The standard metabolic rate and metabolic response to feeding were measured using closed-chamber respirometry. Size changes of small intestine and liver were measured using high-resolution transcutaneous ultrasonography. Standard metabolic rates of fasting egg eaters were in the same range of mass specific values as known from other snakes. Within 24 h after feeding, oxygen consumption doubled and peaked at 2 days after feeding. At the same time, the size of the small intestine and the cross-sectional diameter of the liver increased. Within 2 days after feeding, the size of the mucosal epithelium doubled its thickness. Liver size increased significantly within 24 h reaching maximum size 2–4 days after feeding. The size of both organs returned to fasting values within 7–10 days after feeding. The postprandial response of African rhombic egg eaters shows the same pattern and dynamics as known from other snake species. However, the factorial increase of metabolic rate during SDA is the lowest reported for any snake. A comparison with literature data supports the idea that SDA is mainly determined by gastric function and that it is low in egg eaters because they do not have to break down solid meals in the stomach as other snake species do.     

Adaptation in the African egg-eating snake: a comparative approach to a classic study in evolutionary functional morphology

A key component to any adaptive hypothesis is that the adaptive trait in question must confer a performance advantage and, in turn, an increase in fitness, relative to those animals displaying the phylogenetically antecedent condition. Among the most striking purported adaptations in vertebrates are those found in the African snake genus Dasypeltis . These snakes are unique in that they eat bird eggs to the exclusion of all other prey. Detailed functional morphological analysis dating back 50 years has highlighted a suite of morphological features in the head and trunk region hypothesized to assist these animals in eating bird eggs, and yet no comparative performance studies of egg-eating ability have ever been conducted in this group of snakes. The purpose of this study was twofold: first, we wanted to compare egg-eating performance in Dasypeltis with a facultative egg eater, the common king snake Lampropeltis getula . Second, we wanted to test the hypothesis that a selective regime exists in Africa conducive to the selection and subsequent fixation of the hypothesized egg-eating morphological adaptations. Our results show that a strong advantage exists in egg-eating ability for Dasypeltis . The difference is so large (only large Lampropeltis can eat small eggs) that analysis by analysis of covariance becomes difficult due to problems with collinearity. Our results examining potential selective regimes show that more birds lay eggs of a readily ingestible size in Africa than in a representative region in the United States. Additionally, the largest radiation of African ground-nesting birds existed in Africa before the colubrid explosion during the Miocene, which gave rise to Dasypeltis , giving further support to previous adaptive hypotheses regarding the unique morphology of these snakes.     

Feeding ecology of North American gopher snakes (Pituophis catenifer, Colubridae)

Studies of food relations are important to our understanding of ecology at the individual, population and community levels. Detailed documentation of the diet of large‐bodied, widespread snakes allows us to assess size‐dependent and geographical variation in feeding preferences of gape‐limited predators. Furthermore, with knowledge of the food habits of sympatric taxa we can explore possible causes of interspecific differences in trophic niches. The feeding ecology of the North American gopher snake, Pituophis catenifer, was studied based on the stomach contents of more than 2600 preserved and free‐ranging specimens, and published and unpublished dietary records. Of 1066 items, mammals (797, 74.8%), birds (86, 8.1%), bird eggs (127, 11.9%), and lizards (35, 3.3%) were the most frequently eaten prey. Gopher snakes fed upon subterranean, nocturnal and diurnal prey. The serpents are primarily diurnal, but can also be active at night. Therefore, gopher snakes captured their victims by actively searching underground tunnel systems, retreat places and perching sites during the day, or by pursuing them or seizing them while they rested at night. Gopher snakes of all sizes preyed on mammals, but only individuals larger than 40 and 42 cm in snout–vent length took bird eggs and birds, respectively, possibly due to gape constraints in smaller serpents. Specimens that ate lizards were smaller than those that consumed mammals or birds. Gopher snakes raided nests regularly, as evidenced by the high frequency of nestling mammals and birds and avian eggs eaten. Most (332) P. catenifer contained single prey, but 95 animals contained 2–35 items. Of the 321 items for which direction of ingestion was determined, 284 (88.5%) were swallowed head‐first, 35 (10.9%) were ingested tail‐first, and two (0.6%) were taken sideways. Heavier gopher snakes took heavier prey, but heavier serpents ingested prey with smaller mass relative to snake mass, evidence that the lower limit of prey mass did not increase with snake mass. Specimens from the California Province and Arid Deserts (i.e. Mojave, Sonoran and Chihuahuan Deserts) took the largest proportion of lizards, whereas individuals from the Great Basin Desert consumed a higher percentage of mammals than serpents from other areas, and P. catenifer from the Great Plains ate a greater proportion of bird eggs. Differences in prey availability among biogeographical regions and unusual circumstances of particular gopher snake populations may account for these patterns. Gopher snakes have proportionally longer heads than broadly sympatric Rhinocheilus lecontei (long‐nosed snake), Charina bottae (rubber boa) and Lampropeltis zonata (California mountain kingsnake), which perhaps explains why, contrary to the case in P. catenifer, the smaller size classes of those three species do not eat mammals. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 77 , 165–183.     

Fixed prey cue preferences among Dusky Pigmy Rattlesnakes (<Emphasis Type="Italic">Sistrurus miliarius barbouri</Emphasis>) raised on different long-term diets

Chemoreception is often crucial to the interaction between predators and their prey. Investigating the mechanisms controlling predator chemical preference gives insight into how selection molds traits directly involved in ecological interactions between species. In snakes, prey cue preferences are influenced by both direct genetic control and experience-based plasticity. We assessed prey preference in a group of Dusky Pigmy Rattlesnakes that had eaten only mice or lizards over a 5 year period to test whether genetics or plasticity primarily determine the preference phenotype. Our results provide evidence for genetic determination of preference for lizard chemical cues in pigmy rattlesnakes. Snakes preferred the scent of lizards, regardless of their initial diet, and the response to mouse scent did not differ from the water-only control. We discuss these findings in light of previous studies that manipulated snake diets over shorter timescales.     

Variation in the diet of the viperine snake Natvix mama in relation to prey availability

The diet of the viperine snake was compared with food availability in the Ebro Delta, a wetland largely occupied by rice fields, in 1990 and 1991. Snake selection of prey type and size was studied seasonally and by snake group: males, females and immature snakes. Overall, feeding activity (percentage of individuals with prey and number of prey per stomach) increased with food availability. Diet analysis showed that viperine snakes mainly foraged on the green frog Rana perezi (adults and tadpoles) and the carp Cyprinus earpio. Conversely, viperine snakes rejected the mosquito fish Gambusia holbroki which is the most abundant species in autumn, when Natrix maura has a low feeding activity. Statistical comparisons between viperine snake diet and prey availability showed that males selected small carp, immature snakes selected tadpoles and, in spring, females selected frogs. The selection of small carp by males may reflect a sexual divergence of trophic niche related to sexual size dimorphism, as females are larger than males. As tadpoles are presumably easier to catch than fish, tadpole selection by immature individuals may reflect variance in capture abilities. In spring, the selection of frogs by females overlapped with vitellogenesis, suggesting that females compensate for the cost of reproduction by selecting green frogs, which have a greater biomass and higher energy content than fish. Carps eaten in spring were smaller than in summer. Moreover, in summer viperine snakes selected smaller carp than the available mean size. This divergent tendency between carp size selection and carp size availability reveals how seasonal diet shifts in prey size selection may be a response to an increase in prey size.     

Testing the Threat‐Sensitive Hypothesis with Predator Familiarity and Dietary Specificity

In a system with multiple predators, the threat‐sensitive predator avoidance hypothesis predicts that prey respond differently to predators relative to the risks each poses (e.g., degree of dietary specialization). Aquatic animals often rely heavily on detecting predators via chemical cues (kairomones) and respond with a suite of behaviors including detection and avoidance. However, little is known about how animals respond to kairomones of specialist versus generalist predators. In laboratory experiments, we compared behavioral responses of a poorly studied aquatic salamander, the greater siren (Siren lacertina), to cues from specialist and generalist predator snakes to evaluate threat‐sensitive responses. Sirens exhibited a novel behavior (gill‐flushing) most often in the presence of specialist predator cues. Avoidance behavior (reversing direction following cue detection) was higher in response to specialist predator and novel animal control cues and lowest in response to generalist predator cues. An intermediate response to the animal control, an unfamiliar amphibian predator, indicated that sirens respond cautiously to a novel cue. The gradient of observed responses to different snake cues indicates that sirens may be evaluating predation potential of animals based on their foraging specificity and familiarity.     

Degeneration patterns of the olfactory receptor genes in sea snakes

The sense of smell relies on the diversity of olfactory receptor (OR) repertoires in vertebrates. It has been hypothesized that different types of ORs are required in terrestrial and marine environments. Here we show that viviparous sea snakes, which do not rely on a terrestrial environment, have significantly lost ORs compared with their terrestrial relatives, supporting the hypothesis. On the other hand, oviparous sea snakes, which rely on a terrestrial environment for laying eggs, still maintain their ORs, reflecting the importance of the terrestrial environment for them. Furthermore, we found one Colubroidea snake (including sea snakes and their terrestrial relatives)‐specific OR subfamily which had diverged widely during snake evolution after the blind snake–Colubroidea snake split. Interestingly, no pseudogenes are included in this subfamily in sea snakes, and this subfamily seems to have been expanding rapidly even in an underwater environment. These findings suggest that the Colubroidea‐specific ORs detect nonvolatile odorants.     

Diet of the snake Philodryas nattereri (Steindachner, 1870) suggests a high plasticity of foraging in north-eastern Brazil

The knowledge about interactions between predators and prey is essential for understanding the natural history of animals, especially snakes, which are cryptic organisms that are difficult to visualize in the wild. This article reports on the predation of lizards, frogs, bats and venomous snakes by the snake Philodryas nattereri, evidencing its generalist feeding habits.     

Feeding Strategies in Marine Snakes: An Analysis of Evolutionary, Morphological, Behavioral and Ecological Relationships

Analysis of 1,063 stomach contents from 39 species of sea snakesindicates that about one-third of the shallow, warm, marine,Indo-Australian fish families are preyed upon by sea snakes.Families of eels and gobies are taken by the greatest numbersof snake species. Most species of sea snakes feed on fish familieswhose members are relatively sedentary, dwelling along the bottom,within burrows or reef crevices. With one exception, a fishegg-eating specialization found uniquely in the Aipysurus-Emydocephaluslineage, the dietary habits of sea snakes cannot be categorizedaccording to the snakes' three phylogenetic lineages. Eels,mullet-like, rabbitfish-like and goby-like fish forms are takenby all three lineages. Two or three snake species are generalists,and numerous ones specialize on eels, goby-like fish or catfish.There are differences among sea snake species in the relationshipbetween snake neck girth and the maximum diameter of the prey;in the relationships of both snake gape measurements and fanglength, to the type of prey taken; and in the relationship ofsnake shape and body proportions to the prey selected. Severalmodes of feeding have been observed among sea snakes: feedingin nooks and crannies in the bottom or in reefs, cruising nearthe bottom, and feeding in drift lines. Analysis of percentdigestion of stomach contents and projections backward to thetimes of prey capture provides evidence for feeding periodicity.The greatest amount of diet overlap is for two species of seasnakes which do not both occur at the same locality. Where speciesdo co-occur, diet overlap index values are lower. The numbersof species present as well as their relative abundances varyamong localities as does the relative importance of generalists,eel-eaters, egg-eaters and other specialized feeders.     

Does rock disturbance by superb lyrebirds (Menura novaehollandiae) influence habitat selection by juvenile snakes?

Abstract: Vertebrates that destroy or disturb habitats used by other animals may influence habitat selection by sympatric taxa. In south‐east Australian forests, superb lyrebirds (Menura novaehollandiae) displace soil, leaf litter and rocks during their daily foraging activities. We investigated whether superb lyrebirds disturb small sandstone rocks that endangered broad‐headed snakes Hoplocephalus bungaroides and common small‐eyed snakes Cryptophis nigrescens use as diurnal thermoregulatory sites. To estimate the frequency of lyrebird rock disturbance, and to assess whether lyrebirds also attack small snakes, we placed 900 plasticine snake replicas under stones on rock and soil substrates along transects on three sandstone plateaux. Because juvenile snakes must select retreat sites that simultaneously allow them to thermoregulate and minimize predation risk, we quantified the thermal environments underneath stones on rock and soil substrates. During the 6‐week experiment, animals disturbed rocks on soil substrates twice as often (16.9%) as rocks lying on rock substrates (8.2%). Disturbed rocks were significantly smaller and lighter than undisturbed rocks on both substrates. Lyrebirds were the major agents of disturbance, and attacked 40% of snake models under disturbed rocks. Rocks on soil substrates conferred the greatest thermal benefits to snakes, but both species of snake avoided these microhabitats in the field. Instead, juvenile snakes selected rocks on rock substrates, and sheltered under stones that were too heavy for superb lyrebirds to disturb. By disturbing rocks over millennia, superb lyrebirds not only have shaped the physical landscape, but also may have exerted strong selection on habitat selection by sympatric snakes.     

Can Wall Lizards Combine Chemical and Visual Cues to Discriminate Predatory from Non‐Predatory Snakes Inside Refuges?

The ability to use multiple cues in assessing predation risk is especially important to prey animals exposed to multiple predators. Wall lizards, Podarcis muralis, respond to predatory attacks from birds in the open by hiding inside rock crevices, where they may encounter saurophagous ambush smooth snakes. Lizards should avoid refuges with these snakes, but in refuges lizards can also find non‐saurophagous viperine snakes, which lizards do not need to avoid. We investigated in the laboratory whether wall lizards used different predator cues to detect and discriminate between snake species within refuges. We simulated predatory attacks in the open to lizards, and compared their refuge use, and the variation in the responses after a repeated attack, between predator‐free refuges and refuges containing visual, chemical, or visual and chemical cues of saurophagous or non‐saurophagous snakes. Time to enter a refuge was not influenced by potential risk inside the refuge. In contrast, in a successive second attack, lizards sought cover faster and tended to increase time spent hidden in the refuge. This suggests a case of predator facilitation because persistent predators in the open may force lizards to hide faster and for longer in hazardous refuges. However, after hiding, lizards spent less time in refuges with both chemical and visual cues of snakes, or with chemical cues alone, than in predator‐free refuges or in refuges with snake visual cues alone, but there were no differences in response to the two snake species. Therefore, lizards could be overestimating predation risk inside refuges. We discuss which selection pressures might explain this lack of discrimination of predatory from similar non‐predatory snakes.