Snake Predators Research Articles

Predator-risk-sensitive foraging behavior of Carolina chickadees (Poecile carolinensis) and tufted titmice (Baeolophus bicolor) in response to the head orientation of snake predator models

The risk of predation varies with behavioral cues and body characteristics of potential predators. One such body characteristic is the head/face orientation of the predator. However, a prey individual’s ability to detect the head may be more difficult when the predator’s body is serpentine, with little distinguishing the head from the tail. Here, we tested whether individuals in mixed-species flocks of Carolina chickadees (Poecile carolinensis) and tufted titmice (Baeolophus bicolor) distinguish the head orientation of predator snake models. We conducted behavioral observations at multiple sites each having a bird feeder stocked with seed. Each chickadee and titmouse flock was exposed to two counterbalanced trials: a snake model with head closest to the seed area of the feeder and with tail closest to the seed area of the feeder. Observers recorded the number of seeds taken by each species and also the number of unsuccessful feeder visits. Chickadees and, to a lesser extent, titmice took fewer seeds and had more unsuccessful feeder visits when the head of the snake model was closest to the seed, compared to when the tail was closest to the seed. Titmice, furthermore, had more unsuccessful feeder visits to the black snake model type representing a real snake nest predator for these small songbirds. Therefore, head orientation seems an important factor that some species use to assess predation risk, even for predatory species where head orientation may be a subtle cue.

Evaluating the functional importance of secretive species: A case study of aquatic snake predators in isolated wetlands

AbstractAlthough the need to prioritize limited conservation resources has prompted increased interest in understanding the functional importance of species within ecosystems, species that are infrequently observed are often written off as being unimportant. In this study, we use aquatic snakes as a case study for examining the importance of secretive predators. Most snakes are extremely cryptic and secretive, traits that not only lead to the perception that they are rare, and of minor importance, but also impede attempts to quantify densities. We used high sampling effort and robust‐design capture–recapture analyses to estimate density of aquatic snakes inhabiting an isolated 5.4‐ha wetland in South Carolina, USA. We assessed snake diets and coupled field measurements of growth rates with laboratory‐derived data on mass conversion efficiency to estimate prey consumption by snakes over a 1‐year period. We found a peak density 171 snakes ha−1 of wetland habitat, corresponding to a standing biomass of 7.77 kg ha−1. We calculated that snakes within the wetland consumed a total of over 200 kg (>55 000 individuals) of amphibian prey annually, translating into >150 000 kJ ha−1 of energy flow from secondary to tertiary consumers within the wetland food web. Further, because many amphibians are primarily terrestrial as adults and are consumed by aquatic snakes only when they return to wetlands to breed, snakes can be responsible for substantial transfer of energy and biomass between terrestrial and aquatic habitats. Our study is one of the first comprehensive evaluations of the importance of snakes as predators and underscores the need to consider snakes in initiatives aimed at preserving overall ecosystem integrity.

Preys’ exploitation of predators’ fear: when the caterpillar plays the Gruffalo

Alike the little mouse of the Gruffalo's tale, many harmless preys use intimidating deceptive signals as anti-predator strategies. For example, several caterpillars display eyespots and face-like colour patterns that are thought to mimic the face of snakes as deterrents to insectivorous birds. We develop a theoretical model to investigate the hypothesis that these defensive strategies exploit adaptive cognitive biases of birds, which make them much more likely to confound caterpillars with snakes than vice versa. By focusing on the information-processing mechanisms of decision-making, the model assumes that, during prey assessment, the bird accumulates noisy evidence supporting either the snake-escape or the caterpillar-attack motor responses, which compete against each other for execution. Competition terminates when the evidence for either one of the responses reaches a critical threshold. This model predicts a strong asymmetry and a strong negative correlation between the prey- and the predator-decision thresholds, which increase with the increasing risk of snake predation and assessment uncertainty. The threshold asymmetry causes an asymmetric distribution of false-negative and false-positive errors in the snake-caterpillar decision plane, which makes birds much more likely to be deceived by the intimidating signals of snake-mimicking caterpillars than by the alluring signals of caterpillar-mimicking snakes.

Wait Until Dark? Daily Activity Patterns and Nest Predation by Snakes

AbstractPredation involves costs and benefits, so predators should employ tactics that reduce their risk of injury or death and that increase their success at capturing prey. One potential way that predators could decrease risk and increase benefits is by attacking prey at night when risks may be reduced and prey more vulnerable. Because some snakes are facultatively nocturnal and prey on bird nests during the day and night, they are ideal for assessing the costs and benefits of diurnal vs. nocturnal predation. We used automated radiotelemetry and cameras to investigate predation on nesting birds by two species of snakes, one diurnal and the other facultatively nocturnal. We predicted that snakes preying on nests at night should experience less parental nest defence and capture more adults and nestlings. Rat snakes (Pantherophis obsoletus) were relatively inactive at night (23–36% activity) but nearly always preyed on nests after dark (80% of nest predations). Conversely, racers (Coluber constrictor) were exclusively diurnal and preyed on nests during the times of day they were most active. These results are consistent with rat snakes strategically using their capacity for facultative nocturnal activity to prey on nests at night. The likely benefit is reduced nest defence because birds defended their nests less vigourously at night. Consistent with nocturnal predation being safer, rat snake predation events lasted three times longer at night than during the day (26 vs. 8 min). Nocturnal nest predation did not make nests more profitable by increasing the likelihood of capturing adults or removing premature fledging of nestlings. The disconnect between rat snake activity and timing of nest predation seems most consistent with rat snakes locating prey during the day using visual cues but waiting until dark to prey on nests when predation is safer, although designing a direct test of this hypothesis will be challenging.

Is there more than one way to skin a newt? Convergent toxin resistance in snakes is not due to a common genetic mechanism.

Convergent evolution of tetrodotoxin (TTX) resistance, at both the phenotypic and genetic levels, characterizes coevolutionary arms races between amphibians and their snake predators around the world, and reveals remarkable predictability in the process of adaptation. Here we examine the repeatability of the evolution of TTX resistance in an undescribed predator-prey relationship between TTX-bearing Eastern Newts (Notophthalmus viridescens) and Eastern Hog-nosed Snakes (Heterodon platirhinos). We found that that local newts contain levels of TTX dangerous enough to dissuade most predators, and that Eastern Hog-nosed Snakes within newt range are highly resistant to TTX. In fact, these populations of Eastern Hog-nosed Snakes are so resistant to TTX that the potential for current reciprocal selection might be limited. Unlike all other cases of TTX resistance in vertebrates, H. platirhinos lacks the adaptive amino acid substitutions in the skeletal muscle sodium channel that reduce TTX binding, suggesting that physiological resistance in Eastern Hog-nosed Snakes is conferred by an alternate genetic mechanism. Thus, phenotypic convergence in this case is not due to parallel molecular evolution, indicating that there may be more than one way for this adaptation to arise, even among closely related species.

Nest Defense by a White-rumped Shama (Copsychus malabaricus) Against Snakes

ABSTRACT Snakes represent a serious nest predator to birds. We describe detailed information about interactions between the White-rumped Shama (Copsychus malabaricus) and a nest predator, the Cantor’s Kukri Snake (Oligodon cyclurus) using video recordings. We observed a female White-rumped Shama defending its nest from a Cantor’s Kukri snake by pecking at it when it came within 1 m of the nest. One snake was driven away without consuming a nestling. Two subsequent visits by a larger snake also ended with the snake leaving, but in each attack the snake successfully consumed one nestling. In comparison to findings of an immediate response of other passerines fleeing nests upon snake incursion and subsequent anti-predator attacks, the female shama in this observation attacked the snake predator immediately at its first appearance at the nest.

Experience may allow increasing accuracy of the innate chemosensory recognition of snake predators by Iberian wall lizards

Many animals can recognize chemical cues of predators and show defensive responses, but antipredatory behavior can be costly and should be modulated depending on the level of risk posed by each predatory species. Recognition ability may be innate, but it is not clear whether there might also be local adaptation to predation pressure levels or some learning component. We examined the chemosensory ability of naive and adult Iberian wall lizards, Podarcis hispanicus, to detect chemical cues of two closely related Coronella snake species in two localities within the same continuous population. Lizards in each locality are sympatric with only one of the two snake species. Our results showed an innate chemosensory discrimination of predatory snake cues, as both adult lizards and captive reared naive hatchlings, which had not had any previous experience with the snake cues, had short latencies to the first tongue-flick, increased tongue-flick responses, and active escape behavior from the scent of either of the two snake species. Moreover, adult lizards, but not naive hatchlings, showed differential responses to the two different snake species, with higher responses to the snake species that is sympatric in each locality. This strongly suggests that there is a learning component acquired through previous lifetime experiences that may increase accuracy of the discrimination of the sympatric snake. Therefore, through learning of local conditions, lizards may modulate their innate antipredatory responses to the risk level posed by each snake species.

Visual Detection of Speckles in the Fish Xenotoca variata by the Predatory Snake Thamnophis melanogaster in Water of Different Turbidity.

Semi-aquatic snakes integrate visual and chemical stimuli, and prey detection and capture success are therefore linked to the display of visual predatory behavior. The snake Thamnophis melanogaster responds preferentially to individuals of the fish Xenotoca variata with a greater number of bright, colorful spots (lateral speckles) compared with those with a smaller number; however, water turbidity can reduce underwater visibility and effect the vulnerability of fish. In this study, we tested whether the presence of iridescent speckles on the flanks of male X. variata interacted with water turbidity to modify the predatory behavior displayed by the snake T. melanogaster. We predicted that in an experimental laboratory test, the snakes would increase the frequency of their predatory behavior to the extent that the water turbidity decreases. The snakes were tested at six different levels of water turbidity, in combination with three categories of male fish (with few, a median number of, or many speckles). The results showed that in a pool with high or zero turbidity, the number of speckles is not a determining factor in the deployment of the predatory behavior of the snake T. melanogaster toward X. variata. Our findings suggest that snakes can view the fish at intermediate percentages of turbidity, but the number of speckles in male X. variata is irrelevant as an interspecific visual signal in environments with insufficient luminosity. The successful capture of aquatic prey is influenced by integration between chemical and visual signals, according to environmental factors that may influence the recognition of individual traits.

Assessment of predation risk through referential communication in incubating birds.

Parents of many bird species produce alarm calls when they approach and deter a nest predator in order to defend their offspring. Alarm calls have been shown to warn nestlings about predatory threats, but parents also face a similar risk of predation when incubating eggs in their nests. Here, I show that incubating female Japanese great tits, Parus minor, assess predation risk by conspecific alarm calls given outside the nest cavity. Tits produce acoustically discrete alarm calls for different nest predators: “jar” calls for snakes and “chicka” calls for other predators such as crows and martens. Playback experiments revealed that incubating females responded to “jar” calls by leaving their nest, whereas they responded to “chicka” calls by looking out of the nest entrance. Since snakes invade the nest cavity, escaping from the nest helps females avoid snake predation. In contrast, “chicka” calls are used for a variety of predator types, and therefore, looking out of the nest entrance helps females gather information about the type and location of approaching predators. These results show that incubating females derive information about predator type from different types of alarm calls, providing a novel example of functionally referential communication.

Cooperative rescue and predator fatality involving a group-living strepsirrhine, Coquerel's sifaka (Propithecus coquereli), and a Madagascar ground boa (Acrantophis madagascariensis).

The interactions between primates and their snake predators are of interest because snakes have influenced the evolution of primate visual systems and predation has driven the evolution of primate behaviour, including group living. However, there are few accounts of primate-snake interactions in the wild. We report an incident from Northwest Madagascar in which a large female Madagascar ground boa (Acrantophis madagascariensis) captured an adult female Coquerel's sifaka (Propithecus coquereli); upon capture, the prey's group members proceeded to bite and scratch the snake until it released the prey, which survived. However, a broken mandible suffered by the boa during the incident led to its death by starvation 2 months later. Our observations demonstrate that, in addition to improved predator detection and deterrence (i.e., mobbing), active defence against some predators may provide an additional benefit to group living in Coquerel's sifaka, and suggest that predation on group-living primates may be more costly for predators than attacking a solitary species of similar body size.

Snake predation by the Whistling Heron Syrigma sibilatrix in the Venezuelan Llanos

We describe a predation event on the snake Mastigodryas boddaerty (Colubridae) by the Whistling Heron Syrigma sibilatrix (Ardeidae) in the Venezuelan llanos. The Whistling Heron seems to include snakes occasionally in its diet as indicated by our observation, which also provide the second species of snake recorded in the diet of this heron.

Survivorship and Reproductive Success of Released Laboratory-bred and Native Golden Mice within a Forest-edge Habitat

Abstract We investigated season-of-release effects on survivorship and reproductive success of laboratory-bred compared with a native population of golden mice [Ochrotomys nuttalli (Harlan)] within a deciduous forest habitat. We released two sets of 32 adult pairs of laboratory-bred golden mice into eight experimental transects established in forest-edge habitat. Releases were conducted in early spring (7 Mar. 2009) and late autumn (2 Nov. 2009). Population abundance of laboratory-bred and native golden mice was severely reduced in late spring and summer following the spring release due to black rat snake [Elaphe obsoleta (Stejneger and Barbour)] predation. Laboratory-bred golden mice, however, maintained a stable population density of 15–18 individuals following the late autumn release as snake predation diminished during winter months. The native population of golden mice maintained an abundance of 25–28 individuals through mid-Mar. The laboratory-bred and native populations exhibited similar reproducti...

Snake predation on North American bird nests: culprits, patterns and future directions

Predation is the leading cause of nest failure for most birds. Thus, for ornithologists interested in the causes and consequences of variation in nest success, knowing the identity and understanding the behavior of dominant nest predators is likely to be important. Video documentation of nests has shown that snakes are frequent predators. Here we reviewed 53 North American studies that used nest cameras and used these data to identify broad patterns in snake predation. Snakes accounted for 26% (range: 0–90%) of recorded predation events, with values exceeding 35% in a third of studies. Snakes were more frequent nest predators at lower latitudes and less frequent in forested habitat relative to other nest predators. Although 12 species of snakes have been identified as nest predators, ratsnakes Elaphe obsoleta, corn snakes E. guttata and fox snakes E. vulpina were the most frequent, accounting for > 70% of all recorded nest predation events by snakes and have been documented preying on nests in 30–65% of studies conducted within their geographic ranges. Endotherm‐specialist snakes (Elaphe and Pituophis genera) were more likely to depredate nests in forests and the canopy relative to other snakes, due to their affinity for edge habitat. Predation by only ratsnakes and corn snakes was predominantly nocturnal and only ratsnakes were more likely to prey on nests during the nestling stage. Snakes were not identified to species in over 30% of predation events, underlining the need for more complete reporting of results. A review of research to date suggests the best approach to investigating factors that bring snakes and nests into contact involves combining nesting studies with radio tracking of locally important snake nest predators.

Wary invaders and clever natives: sympatric house geckos show disparate responses to predator scent

The ability to detect and avoid potential predators can enhance fitness, but also has costs, and thus many animals respond to potential predators either in a general (avoid all potential predators) or threat-sensitive (selectively avoid dangerous predators) manner. We used 2-choice trials to investigate strategies used by globally invasive house geckos (Hemidactylus frenatus) and native Australian house geckos (Gehyra dubia) to avoid chemical cues from potential snake predators (Acanthophis antarcticus, Antaresia maculosa, Boiga irregularis, and Pseudechis colletti). Invasive geckos did not respond to a novel chemical cue (perfume), but significantly avoided shelters scented by all 4 predatory snake species, and did not discriminate among snake species that occurred within or outside their current geographic range. Thus, the invasive gecko showed generalized predator avoidance. In contrast, native geckos avoided shelters scented with perfume but did not avoid shelters scented by any of the 4 predatory snake species. We interpret the lack of response by native geckos as threat sensitive, suggesting that they may require additional cues beyond scent alone (e.g., visual cues) to judge the situation as threatening. Generalized responses may be costly for native species living in native habitats filled with predators but may facilitate the rapid establishment of invasive species in novel (especially urban) environments, where general responses to predators may have relatively low costs and enhance survival.

Anti-snake behaviour in a facultative cooperative breeder, the Cape ground squirrel

Predator harassment is an anti-predator behaviour that may increase an individual’s risk of predation, as individuals approach, threaten and harass a potential predator, yet this behaviour is still not well understood. The Cape ground squirrel (Xerus inauris) is a highly social facultative cooperative breeder from southern Africa that harasses several species of venomous snakes. We examined whether harassment was part of alloparental care by comparing harassment behaviours among different age and sex classes in Cape ground squirrel social groups. We also assessed how individuals adjusted their behaviour dependent on levels of risk by examining the Cape ground squirrel’s harassment behaviour among non-venomous, and two species of venomous snakes. We found adult females with emerged juvenile offspring took the most risk, harassing for longer durations and at higher intensities than other group members, suggesting that snake harassment was a maternal behaviour. Females with juvenile offspring only harassed the highest risk elapid snake but increased vigilance and inspection with increasing snake risk suggesting that the Cape ground squirrel can discriminate between different types of snake predators.

Searching for the Audience of the Weeping Lizard's Distress Call

AbstractThe evolution and functions of avian and mammalian antipredator calls are well understood, which contrasts with a lack of progress in reptiles. Here, we present the first investigation of the functions of a distress call in a lizard. We studied Liolaemus chiliensis, which emits a short and complex high‐pitched scream when it is subdued. We determined the behavioral responses of two potential targets to these calls, conspecifics, and a snake predator. Additionally, we tested whether the chemical environment (presence of chemical scents from conspecifics) modulates the lizards' responses to calls. Both the conspecifics and the predator responded to the distress calls, which triggered a longer period of immobility in the lizards and a reduction in exploratory behavior in the snake, as compared to a white noise. In addition, the lizards in the arena with scents of conspecifics responded to distress calls and noise with more movements and escape attempts. These results suggest that distress calls may enhance the survival of L. chiliensis individuals.

Predation of Alouatta puruensis by Boa constrictor

Reports of successful predator attacks on primates are rare. Primates from all major radiations are particularly susceptible to raptors, carnivores, and snakes. Among New World primates, reports of snake predation are limited to medium- and small-bodied species. Here, we report the first documented case of successful predation of an atelid by a snake-an adult female Purús red howler monkey, Alouatta puruensis, that was subdued by a ca. 2-m-long Boa constrictor in an arboreal setting at a height of 7.5 m above the ground. The victim belonged to a group composed of six individuals (one adult male, two adult females, two juveniles, and one infant) that inhabited a ca. 2.5-ha forest fragment in the State of Rondônia, western Brazilian Amazon. The boa applied the species' typical hunting behavior of striking and immediately coiling around its prey and then killing it through constriction (probably in less than 5 min), but the entire restraint period lasted 38 min. The attack occurred around noon. The howler was swallowed head-first in 76 min. The only group member to respond to the distress vocalization emitted by the victim was the other adult female, which was closest to the location where the attack occurred. This female ran toward the snake, also vocalizing, and hit it with her hands several times, but the snake did not react and she moved off to a nearby tree from where she watched most of the interaction. The remaining group members stayed resting at a height approximately 15 m above the victim in a nearby tree without showing any overt signs of stress, except for a single whimper vocalization. This event indicates that even large-bodied atelids are vulnerable to predation by large snakes and suggests that B. constrictor may be a more common predator of primates.

Avian Predation and the Evolution of Life Histories in the Garter Snake Thamnophis elegans

Predation pressure has often been postulated as a major selective force for the evolution of life histories, with high predation (particularly on small sizes) resulting in a fast- living strategy characterized by fast growth, early maturation, and short lifespan. However, due to the difficulty of assessing actual predation pressure in the wild, evidence for a role of predation in life-history evolution is rare. We examined the relationship between avian predation and life-history strategy in replicate populations of fast and slow-living garter snake ecotypes. To assess avian predation, we first compiled a list of known and suspected predators based on direct observations of predation events recorded in our long term detailed field notes from 1978 - present. Furthermore, we added to this list with published records of snake predation involving avian species known to occur in our study site, and a novel method of inferring predator identity via analysis of bill marks on live snakes. Using this list of candidate predators, we conducted surveys quantifying predator incidence in replicate habitats of both ecotypes. We found that known and suspected predators are more abundant in habitats of the fast-living ecotype than in those of the slow-living ecotype. We also show a higher incidence of bill marks on slow-living snakes, which may indicate an increased effectiveness at escaping predation attempts. In general, we provide evidence to suggest that predation pressure may indeed have been an important selective force in the evolution of fast growth and early maturation in the fast-living ecotype and may continue to constitute an important source of extrinsic mortality leading to differences in lifespan between the two ecotypes.

Olfactory Snake‐Predator Discrimination in the Cape Ground Squirrel

AbstractSmall mammals have a number of means to detect and avoid predators, including visual, auditory and olfactory cues. Olfactory cues are particularly important for nocturnal or fossorial species where visual cues would not be as reliable. The Cape ground squirrel (Xerus inauris) is a semi‐fossorial, diurnal mammal from southern Africa. Cape ground squirrels encounter multiple species of predatory snake that pursue individuals underground where visual and social cues are limited. We assessed whether Cape ground squirrels use odours to discriminate between snakes by presenting a non‐venomous snake, a venomous snake and a control odour collected on polyethylene cubes to 11 adult female squirrels from 11 different social groups. Cape ground squirrels responded by inspecting the cube, displaying snake harassment–associated behaviours and decreasing time spent in close proximity to snake odours when compared with a control. They also displayed discrimination between two snake species by increasing the frequency of cube inspection and increasing harassment behaviours with venomous snake odours when compared with non‐venomous snake odours. We conclude that Cape ground squirrels respond with snake‐specific antipredator behaviours when presented olfactory cues alone. Olfactory discrimination may be maintained by the decreased utility of other methods of predator detection: sight and group detection, in below‐ground encounters.

The effects of cues from kingsnakes on the reproductive effort of house mice

Abstract It is not clear if rodents express inducible defenses in response to reptilian predators such as snakes. We tested the hypothesis that adult house mice Mus musculus decrease aspects of their reproductive effort upon 1 hour of exposure every 48 hours for a 25-day period to the fecal material and shed skins of a euryphagous ophidian predator, the kingsnake Lampropeltis getula, that had been fed mice. We found no significant differences in the total number of offspring born, the number of pups per litter, and the mean weight of pups in litters born to male and female mice that were exposed to predator cues and those mice that were not exposed to such cues. The lack of an inducible response may be associated with the low cost of an effective defense, or the lack of an effective defense against a generalist snake predator.