Comparative experimental tests of natricine antipredator displays, with special reference to the apparently unique displays in the Asian genus, Rhabdophis

Nuchal glands are unique organs known in only twelve Old World natricine species (three genera) including Rhabdophis tigrinus tigrinus. The glands of R. t. tigrinus contain a toxic secretion that may be derived from its toxic toad diet. A series of peculiar antipredator behaviors, for example neck arch, neck butt, and dorsal-facing posture, are exhibited by R. t. tigrinus, and a functional association between this behavior and the nuchal glands has been suggested. To investigate the ubiquitousness of these putatively unique displays among snakes, antipredator responses of 27 taxa of natricine snakes, both with and without nuchal glands, were studied using a common testing procedure. Three of four taxa with nuchal glands exhibited neck arch, neck butt, and dorsal-facing posture. None of the remaining 23 taxa, which do not possess the glands, showed neck arch and neck butt. Principal-components analysis indicated the association of the above three displays along with the behaviors termed neck flatten and head elevation, confirming the presence of a series of nuchal gland-related behaviors. These results support the assumption that the suite of peculiar displays is associated with the deterrent effects of the nuchal gland secretion.     

Behavioural responses of an Australian colubrid snake (<Emphasis Type="Italic">Dendrelaphis punctulatus</Emphasis>) to a novel toxic prey item (the Cane Toad <Emphasis Type="Italic">Rhinella marina</Emphasis>)

The invasion of a toxic prey type can differentially affect closely related predator species. In Australia, the invasive Cane Toad (Rhinella marina) kills native anurophagous predators that cannot tolerate the toad’s toxins; but predators that are physiologically resistant (i.e., belong to lineages that entered Australia recently from Asia, where toads of other species are common) have been more resilient. In the current study, we examine the case of an Asian-derived predator lineage that relies on behavioural not physiological adaptations to deal with toads. Despite their Asian origins, Common Tree Snakes (Dendrelaphis punctulatus) are highly sensitive to toad toxins; yet this snake has not declined in abundance due to toads. We exposed captive (field-collected) snakes to toads of different sizes and ontogenetic stages, to quantify feeding responses and outcomes. Tree Snakes were less likely to attack toads than to attack native frogs, and rarely retained their hold on large toads. Tree Snakes ingested frogs of a wide range of body sizes but only ingested very small toads (<?1 g vs. up to 30 g for frogs). Behavioural responses were virtually identical between Tree Snakes from invaded versus yet-to-be-invaded areas, suggesting that preadaptation (from Asia) rather than adaptation (within Australia) is the key to successful utilisation of this novel but potentially toxic prey resource. Nonetheless, a previously-documented shift in relative head sizes of Tree Snakes coincident with toad invasion suggests that the ancestral behavioural tactic may have been reinforced by a recent morphological shift that further reduces maximal prey size, and hence the risk of fatal poisoning.     

Increased Noise Levels Have Different Impacts on the Anti-Predator Behaviour of Two Sympatric Fish Species

Animals must avoid predation to survive and reproduce, and there is increasing evidence that man-made (anthropogenic) factors can influence predator−prey relationships. Anthropogenic noise has been shown to have a variety of effects on many species, but work investigating the impact on anti-predator behaviour is rare. In this laboratory study, we examined how additional noise (playback of field recordings of a ship passing through a harbour), compared with control conditions (playback of recordings from the same harbours without ship noise), affected responses to a visual predatory stimulus. We compared the anti-predator behaviour of two sympatric fish species, the three-spined stickleback (Gasterosteus aculeatus) and the European minnow (Phoxinus phoxinus), which share similar feeding and predator ecologies, but differ in their body armour. Effects of additional-noise playbacks differed between species: sticklebacks responded significantly more quickly to the visual predatory stimulus during additional-noise playbacks than during control conditions, while minnows exhibited no significant change in their response latency. Our results suggest that elevated noise levels have the potential to affect anti-predator behaviour of different species in different ways. Future field-based experiments are needed to confirm whether this effect and the interspecific difference exist in relation to real-world noise sources, and to determine survival and population consequences.     

Leg length and temperature determine the use of unipedal roosting in birds

The function of standing on one leg in birds has long been attributed to reducing heat loss from the unfeathered legs to the external environment. Whilst a handful of single‐species studies correlate the use of the behaviour with ambient temperature, the degree to which it is used across taxa is unknown. Given that leg‐length varies between species, the length of the leg (relative to body size) may mediate the use of this thermoregulatory behaviour, such that birds with longer legs should roost on one leg more than those with relatively shorter legs at any given ambient temperature. We tested this prediction through field observations and comparative analyses of nine shorebird species, with varying tarsi length relative to body size. Six of the nine species examined used unipedal standing more as temperatures decrease, indicating its role as a heat conservation behaviour. We also found that species with relatively longer legs roosted on one leg more frequently across a wide range of temperatures. Species with shorter leg lengths likely rely less on this posture to insulate the relatively smaller surface area of the legs. Our findings showed that the long accepted notion that birds stand on one leg more at colder temperatures holds, and that species with smaller relative leg length were less reliant on this behaviour to minimise heat loss from these bare appendages.     

Traffic noise and responses to a simulated approaching avian predator in mixed-species flocks of chickadees,titmice, and nuthatches

Traffic noise likely reaches a wide range of species and populations throughout the world, but we still know relatively little about how it affects anti-predator behavior of populations. We tested for possible effects of traffic noise on responses to predator acoustic cues in Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white-breasted nuthatches (Sitta carolinensis) near 14 independent feeding stations in eastern Tennessee. We compared anti-predator calling and seed-taking behavior in response to playbacks of predator stimuli (screech owl calls) at sites naturally exposed to traffic noise and at sites that faced relatively little traffic noise. The screech owl call playback was designed to simulate the approach of this dangerous predator to a feeder being used by these small songbirds. We found that chickadees responded consistently to the owl stimuli across different levels of traffic noise. However, titmice, and nuthatches exhibited different behavioral responses to the predator stimulus, suggesting that traffic noise masked these low-frequency predator calls. Overall, chickadees and nuthatches showed the broadest anti-predator behavioral responses in comparison to titmice, corroborating earlier published work with an Indiana population. Finally, populations exposed to traffic noise overall seemed less able to detect predator cues potentially masked by that noise, and future work will need to assess likely seasonal variation in these responses as well as species-level variation in anti-predator responses in mixed-species groups.     

Generalization of predator recognition: Velvet geckos display anti-predator behaviours in response to chemicals from non-dangerous elapid snakes

Many prey species detect chemical cues from predators and modify their behaviours in ways that reduce their risk of predation. Theory predicts that prey should modify their anti-predator responses according to the degree of threat posed by the predator. That is, prey should show the strongest responses to chemicals of highly dangerous prey, but should ignore or respond weakly to chemicals from non-dangerous predators. However, if anti-predator behaviours are not costly, and predators are rarely encountered, prey may exhibit generalised antipredator behaviours to dangerous and non-dangerous predators. In Australia, most elapid snakes eat lizards, and are therefore potentially dangerous to lizard prey. Recently, we found that the nocturnal velvet gecko Oedura lesueurii responds to chemicals from dangerous and non-dangerous elapid snakes, suggesting that it displays gen-eralised anti-predator behaviours to chemicals from elapid snakes. To explore the generality of this result, we videotaped the be-haviour of velvet geckos in the presence of chemical cues from two small elapid snakes that rarely consume geckos: the nocturnal golden-crowned snake Cacophis squamulosus and the diurnal marsh snake Hemiaspis signata. We also videotaped geckos in tri-als involving unsceted cards (controls) and cologne-scented cards (pungency controls). In trials involving Cacophis and Hemi-aspis chemicals, 50% and 63% of geckos spent long time periods (> 3 min) freezing whilst pressed flat against the substrate, re-spectively. Over half the geckos tested exhibited anti-predator behaviours (tail waving, tail vibration, running) in response to Ca-cophis (67%) or Hemiaspis (63%) chemicals. These behaviours were not observed in control or pungency control trials. Our re-sults support the idea that the velvet gecko displays generalised anti-predator responses to chemical cues from elapid snakes. Generalised responses to predator chemicals may be common in prey species that co-occur with multiple, ecologically similar, dangerous predators.     

Increasing temperatures increase the risk of reproductive failure in a near threatened alpine ground-nesting bird,the Cape Rockjumper Chaetops frenatus

A major cause of reproductive failure in birds is nest predation. Predation risk depends on predator type, as predators vary in their ecology and sensory modalities (e.g. visual vs. olfactory). Snakes (generally olfactory predators) are a major nest predator for small birds, with predation strongly associated with higher temperatures. We investigated nest survival in a ground-nesting alpine species, the Cape Rockjumper Chaetops frenatus, endemic to alpine fynbos in southwestern South Africa. We collected 3 years of nest data, testing whether nest survival was related to (1) habitat stage (early post-fire vs. late post-fire habitat, ≤ 3 and > 3 years since fire respectively), (2) nest concealment and (3) temperature. We found that nests had better survival at lower temperatures, with snake predation (our main source of predation) increasing in higher temperatures.     

Negative relationship between ambient temperature and death-feigning intensity in adult Callosobruchus maculatus and Callosobruchus chinensis

Abstract.  Although the effects of temperature on insect behaviours are studied frequently, few studies report on the relationship between temperature and anti-predator behaviours. A negative relationship between ambient temperature and the intensity of death-feigning is found in adults of two seed beetle species, Callosobruchus maculatus (F.) and C. chinensis (L.) (Coleoptera: Bruchidae). Two traits representing the intensity of immobility, the frequency and the duration of death-feigning, are measured at different temperatures. Almost all adults feign death at 15 °C, but the frequency of death-feigning decreases at higher temperatures in C. maculatus , whereas all C. chinensis adults show this behaviour at 15 and 20 °C and almost all show it at 25 °C, but the frequency of death-feigning decreases at 30 and 35 °C. The difference between the two species might be due to the specific strain of each species used in the experiment. The duration of death-feigning is correlated negatively with the increase in ambient temperature in both species. The frequency at which adults feigned death is higher in females than in males in both species, but the duration of death-feigning is higher in females than in males only in C. maculatus . The relationships between temperature and death-feigning behaviours are discussed from physiological and ecological viewpoints.     

一种有毒的游蛇——虎斑颈槽蛇

虎斑颈槽蛇是中国数量较多、分布最广的蛇类之一,但一直被当作无毒蛇而忽视。为了使人们对虎斑颈槽蛇有一个全面、正确的认识,也为以后的相关研究奠定一定的理论基础,从虎斑颈槽蛇的分布,形态,生活习性以及毒腺的研究等方面加以综述。     

Bluffing and Waiting: Handling Effects and Post-Release Immobility in a Death-Feigning Snake (Natrix natrix)

Tonic immobility is a common response of animals to capture by a predator; in some cases, the behaviour is elaborated into death-feigning. Death-feigning is usually interpreted as a last-resort anti-predator tactic that depends on the predator ceasing or slowing its attack when the prey is apparently dead, thus buying time for the prey to escape if the predator's attention is directed elsewhere, even momentarily. I tested the effects of different handling regimes on the expression of death-feigning in the grass snake ( Natrix natrix ). In one test, degree of handling had a significant effect on frequency of death-feigning in small snakes, with snakes that received more handling feigning death more often. A second test showed that different initial handling regimes also affected the probability of death-feigning in large snakes, with snakes initially held by the tail feigning death least frequently and those initially held by the head most frequently. Thus, increased apparent threat to a vulnerable part of the body is more likely to result in death-feigning. It remains to be seen whether death-feigning can reduce the threat posed by real predators, but immobility is frequently carried over into the post-release period, during which the animal presumably weighs its chances and awaits an opportunity to escape. Regardless of cause, death-feigning snakes exhibited significantly more frequent and longer post-release immobility than did non-death-feigning snakes, which typically fled immediately upon release. Overall, small snakes feigned death less frequently than adults and were more likely to flee upon release, suggesting that immobility is a riskier anti-predator defence strategy for them.     

Differential Avoidance of Snake Odours by a Lizard: Evidence for Prioritized Avoidance Based on Risk

Most studies of predator avoidance behaviours have focussed on single‐predator systems, despite the fact that prey often are confronted with predator rich environments. In the presence of more than one predator, prey may have to choose between avoiding one predator over another. How prey cope with exposure to several enemies simultaneously remains largely untested. In this study I set out to investigate if skinks showed preferential avoidance of snake odours based on the relative predation risk posed by different snake species. This relative predation risk was estimated using information on density, diet specificity and foraging habit of each snake species. I tested retreat‐site selection in two‐choice tests, where lizards chose between different combinations of control and snake treated retreat‐sites as well as two retreat‐sites treated with different snake species odours. Lizards preferred control–treated retreat‐sites to those treated with snake odours and showed a differential avoidance response to refuges treated with odours from different snake species. There was strong evidence to suggest that lizards preferentially avoided refuges with the odours of the snake that posed the greatest predation risk, the white‐lipped snake (Drysdalia coronoides). Naïve juvenile lizards were also tested and their response was similar to the adults demonstrating that the behaviour is innate and not the result of higher encounter rates of more common snake odours. To my knowledge this is one of the first studies to demonstrate that prey can prioritize avoidance to a single most dangerous predator in the face of several predators and conflicting avoidance responses.     

Reduction in predator defense in the presence of neighbors in a colonial fish

Predation pressure has long been considered a leading explanation of colonies, where close neighbors may reduce predation via dilution, alarming or group predator attacks. Attacking predators may be costly in terms of energy and survival, leading to the question of how neighbors contribute to predator deterrence in relationship to each other. Two hypotheses explaining the relative efforts made by neighbors are byproduct-mutualism, which occurs when breeders inadvertently attack predators by defending their nests, and reciprocity, which occurs when breeders deliberately exchange predator defense efforts with neighbors. Most studies investigating group nest defense have been performed with birds. However, colonial fish may constitute a more practical model system for an experimental approach because of the greater ability of researchers to manipulate their environment. We investigated in the colonial fish, Neolamprologus caudopunctatus, whether prospecting pairs preferred to breed near conspecifics or solitarily, and how breeders invested in anti-predator defense in relation to neighbors. In a simple choice test, prospecting pairs selected breeding sites close to neighbors versus a solitary site. Predators were then sequentially presented to the newly established test pairs, the previously established stimulus pairs or in between the two pairs. Test pairs attacked the predator eight times more frequently when they were presented on their non-neighbor side compared to between the two breeding sites, where stimulus pairs maintained high attack rates. Thus, by joining an established pair, test pairs were able to reduce their anti-predator efforts near neighbors, at no apparent cost to the stimulus pairs. These findings are unlikely to be explained by reciprocity or byproduct-mutualism. Our results instead suggest a commensal relationship in which new pairs exploit the high anti-predator efforts of established pairs, which invest similarly with or without neighbors. Further studies are needed to determine the scope of commensalism as an anti-predator strategy in colonial animals.     

Do incubation-induced changes in a lizard's phenotype influence its vulnerability to predators?

Strong evidence affirms that incubation temperatures can influence the phenotype of hatchling reptiles, but few studies have examined the fitness consequences of such modifications. Vulnerability to predation is one plausible way that phenotypic shifts could affect an organism's fitness. We incubated the eggs of three sympatric lizard species at temperatures similar to the thermal extremes of natural nests, and measured several traits that are likely to influence a hatchling's susceptibility to a natural (snake) predator. We also examined the lizards' actual vulnerability to snake predators in direct encounters in the laboratory. Our results show that incubation temperature can affect an individual's date of hatching, morphology, locomotor performance, chemosensory responses to snake scent, and ability to avoid a snake predator during staged laboratory encounters. Incubation temperature did not modify the hatchling's `attractiveness' to snakes (as measured via chemical cues) or its antipredator tactics (propensity to escape predation through fleeing or caudal autotomy). The magnitude and direction of incubation- induced phenotypic shifts varied among the three species (even those with similar life histories, thermoregulatory preferences, and microhabitat requirements), and depended on body temperatures and hatchling age. We conclude that incubation-induced modifications to a lizard's phenotype affect a suite of traits that are likely to influence its vulnerability, and also its actual ability to escape from a predator. This result suggests that incubation regimes can influence organismal fitness via their effects on predator-prey interactions. Received: 21 December 1998 / Accepted: 23 March 1999     

Thermoregulation in the Red-beillied Blacksnake, Pseudechis porphyriacus (Elapidae)

Cold Pseudechis porphyriacus aid heating by basking, flattening and tilting. When body temperatures are higher, thermoregulation is achieved by shuttling between sun and shade. A warm snake in a cooling environment frequently coils.
The major factors associated with rate of temperature change in the body core were (1) horizontal gradient between body and neck, (2) posture and (3) vertical gradients from body core to body surface.
The role of behavioral, physiological and physical factors in thermoregulation are discussed.     

萼花臂尾轮虫对晶囊轮虫反捕食行为及形态响应的母体效应

为研究轮虫通过母体效应诱导能否产生行为响应, 以萼花臂尾轮虫(Brachionus calyciflorus)为例, 研究其反捕食漂浮行为响应的母体效应。通过控制轮虫母体在捕食者诱导液中的暴露时间及带卵状态, 收集母体产生的后代, 再将这些后代再次用捕食者诱导液处理, 观察后代的漂浮行为及形态特征。研究发现: 暴露于捕食者诱导液诱导较长时间的母体产生的后代个体, 当再次暴露于捕食者诱导液时, 其产生的行为响应强于没有母体暴露经历的后代; 母体暴露时间越长, 后代形态和行为响应均更加强烈。研究显示萼花臂尾轮虫可通过母体效应产生漂浮行为响应。     

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.     

Threat-sensitive anti-predator defence in precocial wader,the northern lapwing <Emphasis Type="Italic">Vanellus vanellus</Emphasis>

Birds exhibit various forms of anti-predator behaviours to avoid reproductive failure, with mobbing—observation, approach and usually harassment of a predator—being one of the most commonly observed. Here, we investigate patterns of temporal variation in the mobbing response exhibited by a precocial species, the northern lapwing (Vanellus vanellus). We test whether brood age and self-reliance, or the perceived risk posed by various predators, affect mobbing response of lapwings. We quantified aggressive interactions between lapwings and their natural avian predators and used generalized additive models to test how timing and predator species identity are related to the mobbing response of lapwings. Lapwings diversified mobbing response within the breeding season and depending on predator species. Raven Corvus corax, hooded crow Corvus cornix and harriers evoked the strongest response, while common buzzard Buteo buteo, white stork Ciconia ciconia, black-headed gull Chroicocephalus ridibundus and rook Corvus frugilegus were less frequently attacked. Lapwings increased their mobbing response against raven, common buzzard, white stork and rook throughout the breeding season, while defence against hooded crow, harriers and black-headed gull did not exhibit clear temporal patterns. Mobbing behaviour of lapwings apparently constitutes a flexible anti-predator strategy. The anti-predator response depends on predator species, which may suggest that lapwings distinguish between predator types and match mobbing response to the perceived hazard at different stages of the breeding cycle. We conclude that a single species may exhibit various patterns of temporal variation in anti-predator defence, which may correspond with various hypotheses derived from parental investment theory.     

Absence of selective brain cooling in pyrogen-induced fever in rabbits

In 9 rabbits the effect of intravenous administration of E. coli pyrogen 0.5 microgram/kg on the reaction of selective brain cooling was studied at ambient temperatures of 20, 30 and 40 degrees C. In the freely moving animals the temperatures of the brain, carotid artery and nuchal muscles were measured with an accuracy down to 0.05 degree C and the temperatures of the ear pinna and nasal mucosa were measured accurate to 0.5 degree C. The respiratory rate was measured as well. It was found that the spontaneous febrile reaction without the component of passive hyperthermia failed to cause selective brain cooling, even if its temperature reached higher values than in case of brain temperature rise caused only by high ambient temperature. On the other hand, when the high ambient temperature caused thermal panting, pyrogen administration at an ambient temperature of 30 degrees C could reduce panting, while at an ambient temperature of 40 degrees C intense panting initiated prior to the appearance of the febrile reaction and was associated with the fever and outlasted it.     

Parasite-induced alteration of odour responses in an amphipod–acanthocephalan system

Odour-related behaviours in aquatic invertebrates are important and effective anti-predator behaviours. Parasites often alter invertebrate host behaviours to increase transmission to hosts. This study investigated the responses of the amphipod Hyalella azteca when presented with two predator chemical cues: (i) alarm pheromones produced by conspecifics and (ii) kairomones produced by a predatory Green Sunfish (Lepomis cyanellus). We compared the responses of amphipods uninfected and infected with the acanthocepalan parasite Leptorhynchiodes thecatus. Uninfected amphipods reduced activity and increased refuge use after detecting both the alarm pheromones and predator kairomones. Infected amphipods spent significantly more time being active and less time on the refuge than uninfected amphipods, and behaved as if they had not detected the chemical stimulus. Therefore, L. thecatus infections disrupt the amphipods’ anti-predator behaviours and likely make their hosts more susceptible to predation.     

Responses of naïve and experienced European rabbits to predator odour

The response of prey species to predator scent has been investigated in many mammalian species; however, there is little information about the responses of European wild rabbits at the population level. Therefore, we conducted a simple experiment to investigate the behavioural response of a rabbit population to native predator cues in the wild. We compared the response to the scent of a predator (red fox) in a wild rabbit population bred in semi-natural conditions and naïve to terrestrial predators with the response of a population in a similar environment where terrestrial predators were present. The response to predators was based on rabbit abundance, inferred from pellet counts and measured by the defecation rate per day (DRD). Our results indicate that rabbits responded to the odour of fox faeces in the treatment warrens, resulting in a lower DRD. The main anti-predator behaviour observed was spatial avoidance (warren abandonment), which seemed to be more accentuated for rabbits who had not previously had contact with foxes in the plot where terrestrial predators were excluded. In both the fenced and the unfenced plot, the differences in the effect of the predator odour between the control and treatment warrens disappeared after cessation of treatment, suggesting a flexible and adaptive behaviour of rabbits to predator cues.