Snake Predators Research Articles

Chemical Ecology of the North American Newt Genera Taricha and Notophthalmus.

The North American newt genera Taricha and Notophthalmus (order Caudata) are well known for the combination of potent toxicity, aposematic coloration, and striking defense postures that protects these animals from predation. This suite of traits is centered around the neurotoxin tetrodotoxin, which causes paralysis and death in metazoans by disrupting the initiation and propagation of electrical signals in the nerves and muscles. Tetrodotoxin defends newts from predation across multiple life history stages and its role in generating arms-race coevolution between Taricha newts and garter snake (genus Thamnophis) predators is well studied. However, understanding the broader picture of chemical defenses in Taricha and Notophthalmus requires an expanded comprehension of the defensive chemical ecology of tetrodotoxin that includes possible coevolutionary interactions with insect egg predators, protection against parasites, as well as mimicry complexes associated with tetrodotoxin and aposematic coloration in both genera. Herein the authors review what is known about the structure, function, and pharmacology of tetrodotoxin to explore its evolution and chemical ecology in the North American newt. Focus is made specifically on the origin and possible biosynthesis of tetrodotoxin in these taxa as well as providing an expanded picture of the web of interactions that contribute to landscape level patterns of toxicity and defense in Taricha and Notophthalmus.

Snake predators of bird eggs: a review and bibliography

Snake predators of bird eggs: a review and bibliography

ERYTHROLAMPRUS MILIARIS (LINNAEUS, 1758) (SQUAMATA: DIPSADIDAE) A NEW PREY ITEM OF TROPIDURUS TORQUATUS (WIED-NEUWIED, 1820) (SQUAMATA: TROPIDURIDAE) IN SOUTHEASTERN BRAZIL

Although ophiophagy is not a well-known event among neotropical lizards, occasional snake predation events have been reported for some species. For Tropidurus torquatus only one record of predation on Phalotris matogrossensis is currently known. Here we report the second record of ophiophagy in Tropidurus torquatus, adding a new prey item to its known diet, and we provide a review of vertebrate prey consumed by this enigmatic lizard species. Although when compared to other lizard species, T. torquatus has a substantial number of records documenting the predation of small vertebrates, these records are occasional and are likely the result of opportunistic events.

Effect of native and non-native snake scents on foraging activity of native rodents in Florida

Abstract Rodents use direct and/or indirect cues of predators to assess predation risk. The responses to these cues are well studied with regard to mammalian predators, but less understood with regard to reptilian predators. These responses are of particular importance in tropical and subtropical regions where reptile diversity is high and the likelihood of establishment of invasive reptilian predators also is high. We hypothesized that rodents would respond to direct scent cues of snake predators and that rodents would show greater aversion to scents of native snake predators than non-native snake predators. To assess this, scents of three snake species, two native and one non-native, and a non-snake control odor were distributed in Sherman live traps using a randomized block design. A total of 69 rodents representing four species were captured. Responses varied by species reinforcing that some species utilize indirect cues to assess predation risk, whereas others use direct cues. Moreover, one species (Neotoma floridana) showed a preference for non-native Python scent, indicating a lack of the appropriate anti-predator behavior, suggesting that some native rodents are more at risk of attack from invasive snakes than other native rodents.

Behavioral patterns in the early-stage antipredator response change after tail autotomy in adult wall lizards.

Autotomy is a drastic antipredator defense consisting of the voluntary shedding of a body part to escape from the predators. The loss of a body part may impair locomotion, feeding or mating, so animals may face a higher predation risk shortly after autotomy. Thus, until regeneration is completed, prey may adjust their behavior to reduce predation risk, and this could involve secondary costs. We assessed the effect of tail loss on the antipredator behavior of wall lizards (Podarcis muralis), comparing the behavior of tailed and tailless individuals exposed to a predatory snake (Coronella austriaca) scent, under controlled experimental conditions. Tailless lizards spent significantly more time performing behaviors with antipredatory significance (e.g., moving slowly), whereas tailed individuals performed exploratory walking for significantly more time. Moreover, tailless lizards spent more time basking, which probably increases the effectiveness of their cryptic design and decreases detection by predators. Lizards intensified the tongue flick rates when exposed to a pungent control or snake scents, as compared to their response to a neutral control. Besides, both tailed and tailless lizards intensified some aspects of their antipredator behavior (walking slowly and avoiding refuge use) when exposed to snake scent, which indicates discrimination of the smell of predatory snakes. Lizards decreased refuge use when exposed to predator scents, probably because the refuges are evaluated as unsafe due to a high concentration of snake scents. To conclude, our experiments showed that, after losing their tails, wall lizards modify their behavior in a way that likely minimizes predation risk.

Corvid predators may be attracted to parental alarm calls that trigger fledging of nestlings in Oriental Tits (Parus minor)

Predators eavesdropping on prey communication is relatively little studied. Oriental Tits (Parus minor) use “jar” alarm calls toward snake predators near their nests. In response to this call, nestlings fly out of the nest if they are old enough to fledge. After fledging, chicks are vulnerable to predation by corvids. Here we present field observations consistent with the idea that corvids may be attracted to the “jar” alarm calls because these calls predictably trigger fledging of nestlings making them available as prey. Controlled field experiments should test this idea in the future.

Reproductive trade-offs and phenotypic selection change with body condition, but not with predation regime, across island lizard populations.

Trade-offs between reproduction and survival are central to life-history theory and are expected to shape patterns of phenotypic selection, but the ecological factors structuring these trade-offs and resultant patterns of selection are generally unknown. We manipulated reproductive investment and predation regime in island populations of brown anole lizards (Anolis sagrei) to test (1) whether previously documented increases in the survival of experimentally non-reproductive females (OVX=ovariectomy) reflect the greater susceptibility of reproductive females (SHAM=control) to predation and (2) whether phenotypic selection differs as a function of reproductive investment and predation regime. OVX females exceeded SHAM controls in growth, mass gain and body condition, indicating pronounced energetic costs of reproduction. Although mortality was greatest in the presence of bird and snake predators, differences in survival between OVX and SHAM were unrelated to predation regime, as were patterns of natural selection on body size. Instead, we found that body condition at the conclusion of the experiment differed significantly across populations, suggesting that local environments varied in their ability to support mass gain and positive energy balance. As mean body condition improved across populations, the magnitude of the survival cost of reproduction increased, linear selection on body size shifted from positive to negative, and quadratic selection shifted from stabilizing to weakly disruptive. Our results suggest that reproductive trade-offs and patterns of phenotypic selection in female brown anoles are more sensitive to inferred variation in environmental quality than to experimentally induced variation in predation.

Has an invasive lizard lost its antipredator behaviours following 40 generations of isolation from snake predators?

Has an invasive lizard lost its antipredator behaviours following 40 generations of isolation from snake predators?

Combined Effects of Experimentally Elevated CORT and Predation Threat on Exploratory and Foraging Behavior of Desmognathus ochrophaeus

Amphibian responses to stress are generally mediated through glucocorticoids produced by the hypothalamic–pituitary–interrenal axis. Chronic elevation of glucocorticoids can result in delayed wound healing and growth, but less is known about its influence on behavioral responses to predators. We examined the effect of acute and chronic CORT elevation on exploratory and foraging behaviors of Allegheny Mountain Dusky Salamanders (Desmognathus ochrophaeus) exposed to kairomones from a predatory snake. We established ‘No CORT,' ‘Acute CORT,' and ‘Chronic CORT’ conditions during an 18-d preparation phase by varying salamander exposure to an exogenous source of CORT (0.51 mg/mL) delivered via cutaneous patch. During the trial phase, we conducted assays to evaluate exploratory and foraging behavior of salamanders from the different CORT groups when exposed to snake kairomones or control. Exploratory behavior was examined within a circular arena with a series of surmountable concentric barriers, and foraging behavior was observed within Petri dishes containing Drosophila prey. Salamanders experiencing both Chronic CORT and snake kairomones exhibited the least exploratory behavior, escaped the array with the lowest frequency, climbed the fewest barriers, and delayed their movement. However, foraging behavior (latency to strike at prey, number of strikes, number of prey captured) was not affected by exposure to CORT or snake kairomone. Our findings suggest that artificially elevated CORT can modify some behavioral responses to predator kairomones, but only when individuals experience multiple CORT applications in the period preceding the trials.

First record of predation of a hatchling turtle by the Western tiger snake (Notechis scutatus occidentalis).

ABSTRACT Snake-Turtle interactions have been rarely documented. We recorded a hatchling Chelodina oblonga within the stomach contents of a Western tiger snake (Notechis scutatus occidentalis). This is the first recorded observation of an interaction between snakes and hatchling freshwater turtles in Western Australia. Field based palpation failed to detect the hatchling, suggesting that without dissection, turtle hatchling predation by snakes more generally could be higher than commonly reported. Snake predation of hatchlings could be placing additional pressure on threatened populations of freshwater turtles in Australia, warranting further investigation.

Spiders (Arachnida: Araneae) feeding on snakes (Reptilia: Squamata)

In this paper, 319 incidents of snake predation by spiders are reported based on a comprehensive global literature and social media survey. Snake-catching spiders have been documented from all continents except Antarctica. Snake predation by spiders has been most frequently documented in USA (51% of all incidents) and Australia (29%). The captured snakes are predominantly small-sized with an average body length of 25.9 ± 1.3 cm (median = 27 cm; range: 5.8–100 cm). Altogether >90 snake species from seven families have been documented to be captured by >40 spider species from 11 families. About 60% of the reported incidents were attributable to theridiids (≈0.6–1.1 cm body length), a spider family that uses strong tangle webs for prey capture. Especially the Australian redback spider (Latrodectus hasselti Thorell, 1870), the African button spider (Latrodectus indistinctus O. Pickard-Cambridge, 1904), an Israeli widow spider (Latrodectus revivensis Shulov, 1948), and four species of North American widow spiders (Latrodectus geometricus C.L. Koch, 1841, Latrodectus hesperus Chamberlin & Ivie, 1935, Latrodectus mactans (Fabricius, 1775), and Latrodectus variolus Walckenaer, 1837) – equipped with a very potent vertebrate-specific toxin (α-latrotoxin) – have proven to be expert snake catchers. The use of vertebrates as a supplementary food source by spiders represents an opportunity to enlarge their food base, resulting in enhanced survival capability. Interestingly, the snakes captured by spiders also encompasses some species from the families Elapidae and Viperidae known to be highly toxic to humans and other vertebrates. Not only do spiders sometimes capture and kill snakes, quite often the tables are turned – that is, a larger number of arthropod-eating snake species (in particular nonvenomous species in the family Colubridae) include spiders in their diets.

Recent recovery and expansion of Guam’s locally endangered Såli (Micronesian Starling) Aplonis opaca population in the presence of the invasive brown treesnake

SummaryAssessing the impacts of invasive predators on the demography and distribution of native species is critical for understanding mechanisms of species persistence and informing the design of recovery programmes. On the oceanic island of Guam, the introduction of the predatory brown treesnake Boiga irregularis after World War II caused the near-total loss of the native forest avifauna. Localised snake control measures have been implemented since the early 1990s, yet it remains poorly understood how they have impacted Guam’s remaining native bird populations. To address this question, we combined intensive area searches of Andersen Air Force Base (AAFB) with island-wide transect surveys and opportunistic sightings to provide a comprehensive update on the distribution and abundance of Såli (Micronesian Starling, Aplonis opaca) – one of Guam’s last extant native bird species. Area searches of AAFB, where the largest remnant of the Såli population persists, revealed a 15-fold population increase since the last survey in the early 1990s, and transect surveys and opportunistic sightings indicate incipient recolonisation of other urbanised areas of northern and central Guam. We estimate the current island-wide population size at ~1,400 individuals. The population increase can likely be attributed to a combination of snake control measures and the Såli’s ability to exploit urban refugia for nesting and roosting. Although these trends demonstrate some population recovery, a skewed age ratio (>90% adults and subadults) at AAFB and a highly urbanised distribution and low abundance outside AAFB indicate that snake predation continues to strongly impact the population. More intensive snake suppression efforts, particularly in forested areas, may allow for the Såli population to attain its former distribution and abundance on Guam. More broadly, our findings reinforce the importance of urban areas as refugia for some threatened species.

Animal linguistics: Exploring referentiality and compositionality in bird calls

AbstractEstablishing the theory of language evolution is an ongoing challenge in science. One profitable approach in this regard is to seek the origins of linguistic capabilities by comparing language with the vocal communication systems of closely related relatives (i.e., the great apes). However, several key capabilities of language appear to be absent in non‐human primates, which limits the range of studies, such as direct phylogenetic comparison. A further informative approach lies in identifying convergent features in phylogenetically distant animals and conducting comparative studies. This approach is particularly useful with respect to establishing general rules for the evolution of linguistic capabilities. In this article, I review recent findings on linguistic capabilities in a passerine bird species, the Japanese tit (Parus minor). Field experiments have revealed that Japanese tits produce unique alarm calls when encountering predatory snakes, which serve to enhance the visual attention of call receivers with respect to snake‐like objects. Moreover, tits often combine discrete types of meaningful calls into fixed‐ordered sequences according to an ordering rule, conveying a compositional message to receivers. These findings indicate that two core capabilities of language, namely, referentiality and compositionality, have independently evolved in the avian lineage. I describe how these linguistic capabilities can be examined under field conditions and discuss how such research may contribute to exploring the origins and evolution of language.

An opportunist predator hidden in the vegetation: on the predation of birds by Philodryas olfersii (Serpentes: Dipsadidae)

ABSTRACT Snakes are common predators of birds. However, reported cases of snake predation on Troglodytes musculus are scarce. Here, we report a predation attempt of a Troglodytes musculus nestling by the dipsadid snake Philodryas olfersii. We also present a list with bird species recorded as prey of this snake species. We found 25 predation events of P. olfersii on adult, juvenile, and nestling birds. A total of 19 bird species from 14 families have been reported as prey of P. olfersii. Most predation events occurred on the vegetation, while some others were observed on the ground, cage, and artificial nest.

Olfactory lures in predator control do not increase predation risk to birds in areas of conservation concern

Abstract Context Lethal control of predators is often undertaken to protect species of conservation concern. Traps are frequently baited to increase capture efficacy, but baited traps can potentially increase predation risk by attracting predators to protected areas. This is especially important if targeted predators can escape capture due to low trap success. Snake traps using live mouse lures may be beneficial if traps effectively remove snakes in the presence of birds and do not attract additional snakes to the area. Aims The present study evaluated whether mouse-lure traps in areas occupied by birds (simulated by deploying bird-lure traps) could influence predation risk from an invasive snake on Guam. Methods Snake traps were used, with Japanese quail (Coturnix japonica) as a proxy for predation risk, to assess if an adjacent trap with a mouse (Mus musculus) would attract brown treesnakes (Boiga irregularis) to a focal area and increase contact between an invasive snake and avian prey. Catch per unit effort (CPUE) at stations containing either a bird-lure trap, mouse-lure trap or pair of traps (i.e. one bird-lure and one mouse-lure trap) was evaluated. Key results Bird-lure traps paired with mouse-lure traps did not differ in CPUE from isolated bird-lure traps. At paired stations, CPUE of snakes in mouse-lure traps was 2.3× higher than bird-lure traps, suggesting mouse lures were capable of drawing snakes away from avian prey. Bird-lure traps at paired stations experienced a decay in captures over time, whereas CPUE for isolated bird-lure traps increased after 9 weeks and exceeded mouse-lure traps after 7 weeks. Conclusions Mouse lures did not increase the risk of snakes being captured in bird-lure traps. Instead, mouse-lure traps may have locally suppressed snakes, whereas stations without mouse-lure traps still had snakes in the focal area, putting avian prey at greater risk. However, snakes caught with bird lures tended to be larger and in better body condition, suggesting preference for avian prey over mammalian prey in larger snakes. Implications Strategic placement of olfactory traps within areas of conservation concern may be beneficial for protecting birds of conservation concern from an invasive snake predator.

The Horseshoe whip snake (Hemorrhois hippocrepis) on Ibiza: predator release in an invasive population

Abstract The key to fighting a biological invasion may lie in understanding every variable that can explain its success. The Enemy Release Hypothesis (ERH) states that when an invader arrives to a new environment, the absence of its common enemies (predators, parasites and competitors) facilitates the invasion success. The Horseshoe whip snake (Hemorrhois hippocrepis) has been recently introduced from the Iberian Peninsula to the island of Ibiza, and it is currently threatening the only endemic vertebrate, the Ibiza wall lizard (Podarcis pityusensis). We hypothesized that the snake invasion success is caused by the absence of natural predators, and we checked the ERH by relating the tail breakage rate to predation pressure. The invasive population showed a much lower incidence of tail breakage than the source population, which is in agreement with the almost absence of snake predators among the Ibizan reduced and naïve native vertebrate community. These results confirm the ERH, and support the prolongation of invasive snake trapping campaigns.

Life-History Modeling Reveals the Ecological and Evolutionary Significance of Autotomy.

AbstractAutotomy, the self-amputation of body parts, serves as an antipredator defense in many taxonomic groups of animals. However, its adaptive value has seldom been quantified. Here, we propose a novel modeling approach for measuring the fitness advantage conferred by the capability for autotomy in the wild. Using a predator-prey system where a land snail autotomizes and regenerates its foot specifically in response to snake bites, we conducted a laboratory behavioral experiment and a 3-year multievent capture-mark-recapture study. Combining these empirical data, we developed a hierarchical model and estimated the basic life-history parameters of the snail. Using samples from the posterior distribution, we constructed the snail's life table as well as that of a snail variant incapable of foot autotomy. As a result of our analyses, we estimated the monthly encounter rate with snake predators at 3.3% (95% credible interval: 1.6%-4.9%), the contribution of snake predation to total mortality until maturity at 43.3% (15.0%-95.3%), and the fitness advantage conferred by foot autotomy at 6.5% (2.7%-11.5%). This study demonstrated the utility of the multimethod hierarchical-modeling approach for the quantitative understanding of the ecological and evolutionary processes of antipredator defenses in the wild.

Cracking the chemical code: European common lizards (Zootoca vivipara) respond to an hexane soluble predator kairomone

In many animals, chemosensation acts as a first line of defence against snake predators. However, in spite of their obvious importance, the chemical nature of cues used by prey to detect snakes remains to be discovered. Here, we analyse which neutral lipids, extracted with n-hexane, are present in the skin of the European adder (Vipera berus) using Gas Chromatography – Mass Spectrometry. The analyses revealed that the washes held a complex cocktail of chemical compounds, with a total of 165 different molecules, mostly steroids (82% of the total ion current) and alkanes (13%), and smaller amounts of carboxylic acids, wax esters, ketones, amides and alcohols. Using bio-assays in which we confronted individuals of a prey species (the European common lizard, Zootoca vivipara) with these washes, we were able to confirm that the kairomones can be extracted using n-hexane. In fact, lizards did not respond to chemical cues still present in adder skin after washing, indicating that the kairomones are indeed strongly n-hexane soluble. Consequently, we have set a next step in deciphering the chemical nature of the predator-prey interaction between the European adder and the European common lizard. We hope our results facilitate further investigation into the chemical ecology of snakes and their prey.

Physiological Stress Integrates Resistance to Rattlesnake Venom and the Onset of Risky Foraging in California Ground Squirrels.

Using venom for predation often leads to the evolution of resistance in prey. Understanding individual variation in venom resistance is key to unlocking basic mechanisms by which antagonistic coevolution can sustain variation in traits under selection. For prey, the opposing challenges of predator avoidance and resource acquisition often lead to correlated levels of risk and reward, which in turn can favor suites of integrated morphological, physiological and behavioral traits. We investigate the relationship between risk-sensitive behaviors, physiological resistance to rattlesnake venom, and stress in a population of California ground squirrels. For the same individuals, we quantified foraging decisions in the presence of snake predators, fecal corticosterone metabolites (a measure of “stress”), and blood serum inhibition of venom enzymatic activity (a measure of venom resistance). Individual responses to snakes were repeatable for three measures of risk-sensitive behavior, indicating that some individuals were consistently risk-averse whereas others were risk tolerant. Venom resistance was lower in squirrels with higher glucocorticoid levels and poorer body condition. Whereas resistance failed to predict proximity to and interactions with snake predators, individuals with higher glucocorticoid levels and in lower body condition waited the longest to feed when near a snake. We compared alternative structural equation models to evaluate alternative hypotheses for the relationships among stress, venom resistance, and behavior. We found support for stress as a shared physiological correlate that independently lowers venom resistance and leads to squirrels that wait longer to feed in the presence of a snake, whereas we did not find evidence that resistance directly facilitates latency to forage. Our findings suggest that stress may help less-resistant squirrels avoid a deadly snakebite, but also reduces feeding opportunities. The combined lethal and non-lethal effects of stressors in predator–prey interactions simultaneously impact multiple key traits in this system, making environmental stress a potential contributor to geographic variation in trait expression of toxic predators and resistant prey.

Olfactory predator recognition in the brown mouse lemur (Microcebus rufus) in Ranomafana National Park, Madagascar.

Predator odors such as urine and feces are known to elicit antipredator behaviors in prey including avoidance, fear, and curiosity. We measured how wild brown mouse lemurs (Microcebus rufus) responded to odors of mammalian, avian, and snake predators as well as nonpredator controls. The first experiment took place under controlled conditions in a laboratory where we recorded the occurrence of four behavioral categories (ignore, curiosity, alert, and fear) in response to a single odor. Subjects exhibited behavioral change significantly more often in response to the predator than to control stimuli, but did not distinguish between familiar and unfamiliar predators. Mammalian predator urine and feces were most likely to elicit behavioral change. The owl was the only predator to never elicit behavioral change, possibly because owls do not provide relevant odor cues. A second experiment employing live traps in the forest found that neither predator nor control odors affected the likelihood of capture. Due to their longevity, odors do not provide accurate information of spatial and temporal risk, and while mouse lemurs may have initially hesitated to enter a trap, in the absence of additional information about risk, they may have eventually ignored the stimuli. This study found that brown mouse lemurs are able to distinguish between predator and nonpredator odors, and that risk assessment may be affected by the experience, as well as predator and sensory stimulus quality.