Elaphe Obsoleta Research Articles

Environmental Enrichment Alters the Behavioral Profile of Ratsnakes (Elaphe)

This study investigated the effects of environmentally enriched and standard laboratory housing conditions on behavioral performance in 16 subadult ratsnakes (Elaphe obsoleta) using a split-clutch design. In a problem-solving task, snakes housed in enriched environments (EC) exhibited shorter latencies to the goal hole as compared to snakes housed in standard conditions (SC). In an open field task, EC snakes tended to habituate more quickly than SC snakes with repeated testing. A feeding task did not reveal any significant differences between EC and SC snakes. A discriminant function analysis correctly assigned all snakes to their appropriate housing treatment groups, based on the responses in each of the behavioral tasks. This suggests that each group had a distinct behavioral profile; that is, EC snakes were more behaviorally adaptive than SC snakes. This study demonstrated that housing conditions can affect the behavior of captive snakes and produce improvements in behavior similar to those seen in mammalian enrichment studies.

Patterns of Snake Predation at Songbird Nests in Missouri and Texas

Snakes are frequent predators of eggs and nestlings, but general patterns of snake predation at bird nests are not well known. We reviewed 84 video observations of snakes visiting nests of four songbird species in Texas and Missouri to identify patterns of predatory behavior. Eastern Ratsnakes (Elaphe obsoleta) were the most common species, and coachwhips, racers, kingsnakes, and a garter snake also were recorded. Snakes almost always removed all nest contents during a single visit but sometimes force-fledged nestlings that were old enough to escape. During many visits late in the nestling period, snakes pinned their prey in the nest while feeding, thereby preventing many of the young from escaping. Snakes spent an average of 13 min and 23 sec at each nest (1 min and 52 sec before striking), and the duration of nocturnal visits exceeded the duration of diurnal visits. Snakes sometimes returned to empty nests after they caused failure but only after nestlings were depredated. Visits by Texas Ratsnakes (Elaphe obsoleta lindheimeri) were mostly nocturnal, whereas visits by Black Ratsnakes (Elaphe obsoleta obsoleta), coachwhips, racers, and kingsnakes were diurnal. Snake predation increased as the nesting cycle progressed with the highest rate occurring in the last few days of the nestling period. Increased predation at the end of the nestling period suggests that avian activity (i.e., feeding visits, nest defense, and nestling movement) contributes to the foraging success of snakes at our sites.

ABSENCE OF DETECTABLE SALMONELLA CLOACAL SHEDDING IN FREE-LIVING REPTILES ON ADMISSION TO THE WILDLIFE CENTER OF VIRGINIA

Salmonellosis is an important reptile-associated zoonotic infection in the United States. Cloacal swabs were collected from reptiles admitted to the Wildlife Center of Virginia, Waynesboro, Virginia, cultured for Salmonella using Hektoen and xylose lysine deoxycholate agars, and inoculated in selenite broth. All three were incubated at 37 degrees C for 18-24 hr. Seventy-five animals were included in the study, representing eight species, 34 eastern box turtles (Terrapene carolina carolina), 14 eastern painted turtles (Chrysemys picta picta), 14 snapping turtles (Chelydra serpentina), 6 black rat snakes (Elaphe obsoleta obsoleta), 2 redbelly turtles (Pseudemys rubriventris), 2 yellowbelly sliders (Trachemys scripta scripta), 2 eastern garter snakes (Thamnophis sirtalis sirtalis), and 1 eastern river cooter (Pseudemys concinna concinna). All cultures were negative for Salmonella spp., which is in contrast to the high prevalence of Salmonella cloacal shedding reported in captive reptiles but similar to previous reports in free-living North American reptiles. We recommend, nonetheless, practicing proper hygiene methods when handling and housing all reptiles.

Genetic evidence for sexual selection in black ratsnakes, Elaphe obsoleta

We investigated benefits of polyandry and phenotypic correlates of male mating success in black ratsnakes. We used 10 microsatellite loci to identify the sires of 375 hatchlings from 34 clutches with known mothers. Multiple paternity occurred in 88% of clutches, despite the fact that ratsnakes mate when dispersed. The incidence of multiple paternity did not vary with female size or with clutch size. Hatching success tended to be higher in multiply sired clutches, but offspring from these clutches were not longer or heavier. We identified 34 males as the sires of 144 hatchlings. Most instances where sires could not be identified resulted from exclusion of all 426 potential sires that we screened. Unidentified sires were probably males that hibernated outside our study area and thus were not included in the intensive sampling at hibernacula in the study area. Among males that sired offspring, body size but not tail length contributed to success, consistent with male-biased sexual size dimorphism and male–male combat shown by this species. Large males were more successful primarily by siring more offspring per clutch rather than by siring offspring in more clutches. This may be a result of greater success in sperm competition. Neither body condition nor genetic similarity to the female was related to male mating success. Our results, in conjunction with published data on movement patterns, suggest that snakes of both genders can benefit from actively seeking multiple matings.

Long-term effects of radiotelemetry on black ratsnakes

We assessed the effect of radiotelemetry on the growth, reproduction, and survival of black ratsnakes (Elaphe obsoleta) using data from a 6-year study. Transmitters were surgically implanted for more than one year and were <2.5% of the snakes' mass and 3.8% of their length. Compared to snakes without transmitters, snakes with transmitters exhibited lower annual growth in mass but not length, and females produced lighter clutches of eggs relative to their body size. Although results were equivocal, radiotelemetry also may have adversely affected survival. Potential explanations for the negative effects of radiotelemetry include direct effects of transmitters on snakes (impaired behavior, cost of transportation, infection) and indirect effects (increased disturbance by researchers). Because we conducted the study at the northern limit of the species' distribution, snakes in this population may be particularly sensitive to the negative effects of radiotelemetry. Despite the apparent costs, we believe that use of radiotelemetry is still warranted because of the benefits realized.

Phenotypic consequences of nest-site selection in black rat snakes (Elaphe obsoleta)

Nest-site selection is the only behaviour that can be considered parental care in most oviparous reptiles because eggs are abandoned after laying and because incubation conditions resulting from nest-site selection can have profound effects on offspring. During a 7-year study of black rat snakes, Elaphe obsoleta (Say in James, 1823), we investigated phenotypic effects of incubation temperature on hatchlings, monitored temperatures in nests, and determined the preferred nesting temperature. Temperatures of communal nests were higher than those of single-female nests. In the laboratory, females preferred to nest at temperatures most similar to those of communal nests. Hatchlings from eggs incubated at temperatures similar to those in the warmer communal nests hatched faster, were longer, swam faster, were less aggressive, and had fewer scale anomalies than hatchlings from eggs incubated at temperatures similar to those in single nests. A possible disadvantage of communal nests is that eggs in communal nests may be at greater risk to parasitism by Nicrophorus pustulatus (Herschel, 1807). The incubation experiment allowed a test of a key assumption of a model proposed to explain environmental sex determination. Contrary to that assumption, we found no evidence that incubation temperature affected males and females differently. Our results might explain why temperature-dependent sex determination appears not to occur in snakes.

Surgical Removal of an Artificial Chicken Egg from the Gastrointestinal Tract of a Black Rat Snake, Elaphe obsoleta

ABSTRACT A black rat snake, Elaphe obsoleta, with a three month history of a gastrointestinal foreign body was presented for evaluation. Radiographs and surgery were performed to remove an artificial chicken “egg” from the lumen of the intestine. The snake recovered uneventfully and remains healthy.

Seasonal and Prey-size Dietary Patterns of Black Ratsnakes (Elaphe obsoleta obsoleta)

Black ratsnakes (Elaphe obsoleta obsoleta) prey extensively on both birds (eggs and nestlings) and mammals. There is conflicting evidence, however, regarding whether the snakes specialize on birds during the birds' nesting season or whether predation on birds is opportunistic. We tested these alternatives by determining seasonal dietary patterns from 81 fecal samples collected from black ratsnakes in eastern Ontario over 4 y. We also used these data to determine how diet varies with snake size. Birds occurred in the snakes' diet from May through August, but the occurrence of birds never exceeded that of mammals in any month. This pattern was the same as that previously reported for black ratsnakes in Kansas and supports the hypothesis that black ratsnakes prey on birds opportunistically. Relative to smaller individuals, larger ratsnakes preyed on larger species of mammals and reduced their consumption of smaller species of mammals. The reduction in the consumption of small prey by large snakes was due to diet diversification rather than specialization. However, because larger snakes continued to include small prey in their diet, predation patterns on birds and mammals suggest that ratsnakes are opportunistic predators.

A test of the thermal coadaptation hypothesis with black rat snakes ( Elaphe obsoleta) and northern water snakes ( Nerodia sipedon)

1. The thermal coadaptation hypothesis predicts that (1) ectotherms experiencing a narrow range of body temperatures in the wild will evolve to perform well over a narrow range of body temperatures and that (2) the optimal temperature for performance will be equal to the preferred body temperature of the species. 2. We tested the predictions of the thermal coadaptation hypothesis with black rat snakes ( Elaphe obsoleta) and northern water snakes ( Nerodia sipedon) because black rat snakes experience lower and more variable body temperatures than northern water snakes at our study site. 3. We measured swimming speed, tongue-flicking speed, and striking speed in black rat snakes, and swimming speed and tongue-flicking speed in northern water snakes. 4. Adult water snakes generally had narrower performance breadths and higher optimum performance temperatures than adult black rat snakes. 5. Performance breadths were the same for swimming, tongue flicking, and striking within adult black rat snakes, but performance optima for these behaviours differed significantly. Performance breadths differed and performance optima were the same for swimming and tongue flicking within adult northern water snakes. 6. The relative swimming performance of neonates of the two species was similar in breadth to that of adults, but the thermal optimum for neonate black rat snakes was higher than that of adults. 7. Overall, our results provided support for the thermal coadaptation hypothesis.

Isolation and characterization of microsatellite loci in the black rat snake (Elaphe obsoleta)

AbstractWe obtained molecular markers useful for population level studies of the black rat snake (Elaphe obsoleta) by screening genomic DNA libraries enriched for dinucleotide, tetranucleotide, and pentanucleotide microsatellite repeats. Following sequencing of the positive clones, 11 pairs of primers were designed for polymorphic loci and their variability assessed in &gt; 350 individuals from four populations in North America. The loci had between 9 and 40 alleles and observed heterozygosities ranged from 0.071 to 0.87. Some of these pairs of primers also successfully amplified DNA from two other snake species.

Implications of movement patterns for gene flow in black rat snakes (Elaphe obsoleta)

Gene flow is fundamental to evolutionary processes but knowledge about movements of individuals and their offspring necessary for gene flow is scant. We investigated potential ecological components of genetic connectivity within a population of black rat snakes (Elaphe obsoleta) by radio-tracking 82 individuals. Because adult black rat snakes are highly faithful to their hibernaculum, gene flow between hibernaculum populations has to occur through mating between members of different hibernacula or through juvenile dispersal. The present study was the first to assess the spatial dispersion of a complete network of hibernacula. The mean distance between the nearest-neighbour hibernacula was 811 m, which was less than the mean distances that reproductive males and females were found from their hibernacula during the mating season. Estimates of maximum distances individuals were from their hibernacula during the mating season indicated that, on average, a female was likely to mate with males that came from two hibernacula away from the female's own hibernaculum. Both males and females appeared to contribute actively to gene flow by moving more and increasing their distance from their hibernacula during the mating season. In addition, on average, females nested closer to a hibernaculum other than the one they attended, thereby potentially increasing the likelihood that their offspring would join hibernacula other than their mothers'. Thus, spatial and movement patterns of male and female black rat snakes are consistent with genetic evidence of extensive out-breeding among local hibernaculum populations.

Barking up the wrong tree: climbing performance of rat snakes and its implications for depredation of avian nests

Nest depredation is the leading cause of nest failure in Neotropical–Nearctic migratory birds, which are of interest because of their declining populations. In a recent study in a bottomland hardwood forest, Acadian Flycatchers (Empidonax virescens) experienced higher nest success in Nuttall oak (Quercus nuttallii), a tree species with relatively smooth bark at maturity. To determine if variation in bark-surface irregularities may influence the ability of a predator species to access the contents of avian nests, we examined the climbing abilities of rat snakes (Elaphe obsoleta) on trees having three different bark types. None of the subjects was able to ascend large Nuttall oaks in the absence of vines; with vines present, subjects still required more time to climb Nuttall oaks than to climb other species. A few of the subjects successfully climbed smaller Nuttall oaks lacking vines, but ascent time was longer and climbing behavior was modified from that observed in the other trials. Our results indicate that the likelihood of nest predation by rat snakes decreases in this forest when birds nest in trees with smooth bark and without vines. Investigators need to consider differences among nest substrates that are important to both the prey and the predator.

Comparative demography of black rat snakes (Elaphe obsoleta) in Ontario and Maryland

AbstractThis study investigated how demographic characteristics of black rat snakes Elaphe obsoleta are affected by the length of the active season, and also used the resulting demographic data to determine the proximate factors responsible for male‐biased sexual size dimorphism (SSD) in the species. Demographic data collected from 1981 to 1998 in Ontario (ON; 583 males and 588 females) and from 1942 to 1976 in Maryland (MD; 180 males and 150 females) were used to develop growth models with the von Bertalanffy growth equation. Instantaneous growth rates declined significantly with increasing snout–vent length (SVL) in males and females of each population. The growth models predicted age using SVL satisfactorily, but the accuracy of the model decreased significantly with increasing SVL. As predicted, based on the brevity of their active season (ON ≊ 135 days, MD ≊ 190 days), rat snakes of both sexes from Ontario had lower and more variable instantaneous growth rates and matured at a more advanced age (ON ≊ 9 years, MD ≊ 4 years) than snakes from Maryland. However, the rapid growth and early maturation in Maryland snakes occurred at the expense of longevity (maximum: ON ≊ 30 years, MD ≊ 20 years). Slower growth and later maturation will make rat snakes in Ontario less capable of recovering from population declines. Within each population, males grew faster than females. Survivorship for Ontario snakes did not vary by sex, but increased significantly with increasing SVL. The demographic consequence of sex differences in growth was a male‐biased sex ratio among larger snakes. Because SSD is a function of males growing faster than females, SSD in black rat snakes is probably a product of sexual selection, suggesting that large size confers a mating advantage in males.

Thermal Ecology of Black Rat Snakes (Elaphe obsoleta) in a Thermally Challenging Environment

Thermal Ecology of Black Rat Snakes (Elaphe obsoleta) in a Thermally Challenging Environment

An experimental test of the link between foraging, habitat selection and thermoregulation in black rat snakes Elaphe obsoleta obsoleta

Summary Most physiological processes are temperature‐dependent. Thus, for ectotherms, behavioural control of body temperatures directly affects their physiology. Ectotherms thermoregulate by adjusting habitat use and therefore thermoregulation is probably the single most important proximate factor influencing habitat use of terrestrial reptiles, at least in temperate climates. Snakes have been shown to raise their body temperature following feeding in a laboratory thermal gradient, presumably to enhance digestion. This experiment was exported to the field to explore the link between feeding, habitat selection and thermoregulation in free‐ranging snakes. Experimental feeding was conducted in the laboratory and in the field on black rat snakes (Elaphe obsoleta obsoleta) that had temperature‐sensitive radio‐transmitters surgically implanted. Snakes had higher mean body temperatures following feeding than prior to feeding in a laboratory thermal gradient. Some, but not all evidence, indicated that black rat snakes increased their mean body temperature following feeding in the field. Indices of thermoregulation indicated that the snakes thermoregulated more carefully and more effectively after they had eaten. Forest edges provided the best opportunities for thermoregulation in the study area. Black rat snakes were less likely to move following feeding when fed in edges than when fed in the forest and were more likely to be found in edges following feeding, whether they had been fed in the forest or in an edge. Results of this study and one previous study suggest that thermoregulatory behaviour of snakes following feeding in the laboratory is a reliable predictor of their behaviour in the field. A review of 13 studies of the thermoregulatory behaviour of snakes following feeding in the laboratory revealed that not all species behave similarly. However, the quality and number of studies currently available is not adequate for testing hypotheses about which species should change thermoregulatory behaviour in response to eating and which should not.

HABITAT USE BY BLACK RAT SNAKES (ELAPHE OBSOLETA OBSOLETA) IN FRAGMENTED FORESTS

Declining nest success of forest birds in fragmented habitat has been attri- buted to increased nest predation. Better understanding of this problem and potential so- lutions to it require information on why nest predators are attracted to habitat edges. Toward this end we investigated habitat use by black rat snakes (Elaphe obsoleta obsoleta), an important avian-nest predator in eastern deciduous forests. We radio-tracked 52 black rat snakes for periods of 3-41 mo from 1996 to 1999. All black rat snakes exhibited a strong preference for edge habitats. Consistent with edges being used because they facilitate thermoregulation, gravid females associated more strongly with edges than did males and nongravid females, and sites used by snakes when shedding were significantly associated with habitat edges. Gravid females lost an average of >20% of their body mass, while nongravid females and males did not lose mass, suggesting that edges were not used because they offered high success in foraging. Similarly, an increase in use of edge habitat through the season by all rat snakes was inconsistent with the snakes being attracted principally to hunt: avian prey would have been more abundant in spring when birds were breeding, and the density of small mammals in edges did not vary seasonally. Also, snakes moved longer distances and were found traveling.more often when located in forests. Because our results collectively are most consistent with the hypothesis that rat snakes use edges for ther- moregulatory reasons, the negative impact of the snakes on nesting birds may be coinci- dental; the snakes primarily use edges for reasons other than foraging but opportunistically exploit prey they encounter there. Rat snakes appeared to respond to the edge structure rather than to how the edge was created (natural vs. artificial). Thus, fragmentation of forests by humans has created habitat structurally similar to that preferred by rat snakes in their natural habitat, thereby inadvertently increasing contact between the snakes and nesting birds.

Systematics of the Eastern Ratsnake Complex (Elaphe obsoleta)

The eastern ratsnake, Elaphe obsoleta currently includes seven highly variable and taxonomically confusing subspecies. Recently, maximum likelihood and maximum parsimony phy- logenetic analyses of two mitochondrial gene sequences suggested that the complex of E. obsoleta (including E. bairdi) is composed of four distinct evolutionary lineages found in four geographical areas: 1) an eastern clade located east of the Apalachicola River and the Appalachian Mountains, 2) a central clade located west of the Apalachicola River and the Appalachian Mountains and east of the Mississippi River, 3) a western clade located west of the Mississippi River, and 4) E. bairdi is located in southwest Texas and northeastern Mexico. With respect to this phylogeographic hy- pothesis, the former seven subspecies of E. obsoleta do not represent distinct evolutionary lineages. In this paper, the morphology of Elaphe obsoleta and E. bairdi is compared to the results of the previous molecular study. Univariate and multivariate analyses of 67 morphological characters scored from 1006 specimens provided statistical support for the recognition of the same four evolutionary lineages identified in the phylogeographic study. Specimens can be classified morphologically by using canonical discriminant function analysis into the four molecular clades more accurately than they can be grouped into subspecific categories. Moreover, the identification of these subspecies proved difficult when using the traditional characters ascribed to them. In light of the corroborating molecular and morphological evidence, it is suggested that the recognition of the subspecies of E. obsoleta be discontinued. Instead, the four molecular clades should be recognized as four species: 1) eastern clade = E. alleghaniensis, 2) central clade = E. spiloides, 3) western clade = E. obsoleta, and 4) E. bairdi = E. bairdi.

MITOCHONDRIAL DNA PHYLOGEOGRAPHY OF THE POLYTYPIC NORTH AMERICAN RAT SNAKE (ELAPHE OBSOLETA): A CRITIQUE OF THE SUBSPECIES CONCEPT

Subspecies have been considered artificial subdivisions of species, pattern classes, or incipient species. However, with more data and modern phylogenetic techniques, some subspecies may be found to represent true species. Mitochondrial DNA analysis of the polytypic snake, Elaphe obsoleta, yields well‐supported clades that do not conform to any of the currently accepted subspecies. Complete nucleotide sequences of the cytochrome b gene and the mitochondrial control region produced robust maximum‐parsimony and maximum‐likelihood trees that do not differ statistically. Both trees were significantly shorter than a most parsimonious tree in which each subspecies was constrained to be monophyletic. Thus, the subspecies of E. obsoleta do not represent distinct genetic lineages. Instead, the evidence points to three well‐supported mitochondrial DNA clades confined to particular geographic areas in the eastern United States. This research underscores the potential problems of recognizing subspecies based on one or a few characters.

Habitat Use by Three Species of Snakes at the Middle Fork Fish and Wildlife Area, Illinois

We used radiotelemetry to determine habitat use by 11 black rat snakes (Elaphe obsoleta obsoleta), five fox snakes (Elaphe vulpina vulpina) and four blue racers (Coluber constrictor foxii) at the Middle Fork Fish and Wildlife Area in east-central Illinois in 1997 and 1998. Black rat snakes selected forested habitats, whereas fox snakes and blue racers selected old fields and prairie restorations. No consistent association with forest- field edges was noted for any species. Fox snakes and blue racers were primarily terrestrial, whereas black rat snakes used all categories of vertical space but were primarily arboreal. Snakes were tracked to three hibernation sites, including an abandoned railroad trestle and two abandoned trash and construction-material dumps. These data provide the first comparative, quantitative descriptions of habitat use for these species in sympatry, and one of the few descriptions of hibemacula in a region dominated by row-crop agriculture. Due to their secretive behavior, snakes are difficult to study in the field and many impor- tant features of their ecology and natural history are not well known (Seigel et al., 1987; Seigel and Collins, 1993). Snakes also are frequently considered vermin and often indiscriminately killed by humans (Dodd, 1987; Greene, 1997). Because many species of snakes are declining in numbers (Dodd, 1987; Greene, 1997), it is im- portant to identify and protect critical habitats and landscape features relevant to their conser- vation. In temperate regions, sites used as hi- bemacula may be particularly important to the persistence of populations of many species of snakes (e.g., Prior and Weatherhead, 1996; Bur- brink et al., 1998). However, little information exists about habitat selection and sites used as hiberacula by snakes in agricultural regions of the midwestern United States.

Plasticity in Preferred Body Temperature of Young Snakes in Response to Temperature during Development

Abstract We investigated whether the thermal history of Black Rat Snakes (Elaphe obsoleta) and Northern Water Snakes (Nerodia sipedon) during development affected their preferred body temperatures (PBT) after hatching or birth. Eggs of black rat snakes were incubated at high or low temperatures. Gravid female water snakes were maintained in rooms under low, medium, or high ambient temperatures. PBT of neonates were measured in a controlled thermal gradient. We only found plasticity in PBT with developmental temperature for northern water snakes, where offspring that developed under warmer temperatures demonstrated a significant preference for warmer temperatures. Our results suggest that PBT are plastic in only some species of snakes and may explain some of the individual variation in PBT observed in adult snakes.