Texas Ratsnakes Research Articles

Characterization of the Leucistic Texas Rat Snake Pantherophis obsoletus

Albinism and leucism are phenotypes resulting from impaired melanin pigmentation in the skin and skin appendages. However, melanin pigmentation of eyes remains unaffected in leucism. Here, using transmission electron microscopy, we show that the leucistic morph of the Texas rat snake (Pantherophis obsoletus lindheimeri) lacks both melanophores and xanthophores in its skin and exhibits a uniform ivory white color generated by iridophores and collagen fibers. In addition, we sequenced the full genome of a leucistic individual and obtained a highly-contiguous near-chromosome quality assembly of 1.69 Gb with an N50 of 14.5 Mb and an L50 of 29 sequences. Using a candidate-gene approach, we then identify in the leucistic genome a single-nucleotide deletion that generates a frameshift and a premature termination codon in the melanocyte inducing transcription factor (MITF) gene. This mutation shortens the translated protein from 574 to 286 amino acids, removing the helix-loop-helix DNA-binding domain that is highly conserved among vertebrates. Genotyping leucistic animals of independent lineages showed that not all leucistic individuals carry this single-nucleotide deletion. Subsequent gene expression analyses reveal that all leucistic individuals that we analyzed exhibit a significantly decreased expression of MITF. We thus suggest that mutations affecting the regulation and, in some cases, the coding sequence ofMITF, the former probably predating the latter, could be associated with the leucistic phenotype in Texas rat snakes.MITFis involved in the development and survival of melanophores in vertebrates. In zebrafish, a classical model species for pigmentation that undergoes metamorphosis, larvae and adults of homozygousmitfamutants lack melanophores, show an excess of iridophores and exhibit reduced yellow pigmentation. On the contrary, in the leucistic Texas rat snake, a non-metamorphic species, only iridophores persist. Our results suggest that fate determination of neural-crest derived melanophores and xanthophores, but not of iridophores, could require the expression ofMITFduring snake embryonic development.

PREDATION ON NORTHERN BOBWHITE AND SCALED QUAIL BY SNAKES IN TEXAS, USA

Snakes are a known predator of quail; however, the influence of snake predation on quail populations is unknown. We used a long-term data set collected by eight radiotelemetry studies in Texas, encompassing 23 years (1994–2017) and 5,369 quail, to quantify snake predation on quail. We documented that northern bobwhite (Colinus virginianus) and scaled quail (Callipepla squamata) mortalities were caused by three species: western diamondback rattlesnakes (Crotalus atrox), prairie rattlesnakes (Crotalus viridis viridis), and Texas rat snakes (Pantherophis obsoletus). This study is the first to document predation of quail (Odontiphoridae) by the latter two species. We found 30 mortalities (0.6%) attributable to western diamondback rattlesnakes. We found 1 mortality (0.03%) attributable to a prairie rattlesnake and 2 mortalities (0.06%) attributable to Texas rat snakes of the 3,206 quail exposed to predation by those two species. We concluded that snakes are not major predators of adult quail, but that they will prey opportunistically upon them.

Debunking the viper's strike: harmless snakes kill a common assumption.

To survive, organisms must avoid predation and acquire nutrients and energy. Sensory systems must correctly differentiate between potential predators and prey, and elicit behaviours that adjust distances accordingly. For snakes, strikes can serve both purposes. Vipers are thought to have the fastest strikes among snakes. However, strike performance has been measured in very few species, especially non-vipers. We measured defensive strike performance in harmless Texas ratsnakes and two species of vipers, western cottonmouths and western diamond-backed rattlesnakes, using high-speed video recordings. We show that ratsnake strike performance matches or exceeds that of vipers. In contrast with the literature over the past century, vipers do not represent the pinnacle of strike performance in snakes. Both harmless and venomous snakes can strike with very high accelerations that have two key consequences: the accelerations exceed values that can cause loss of consciousness in other animals, such as the accelerations experienced by jet pilots during extreme manoeuvres, and they make the strikes faster than the sensory and motor responses of mammalian prey and predators. Both harmless and venomous snakes can strike faster than the blink of an eye and often reach a target before it can move.

Preferred nest site characteristics reduce predator-specific predation risk in a canopy-nesting raptor

Habitat features influence nest survival and, as a result, identifying relationships between habitat characteristics and nest survival remains a central focus among studies of avian reproduction. In cases where nest predation is the main cause of failure, knowing how the habitat affects predation risk may provide managers with a tangible means by which to improve reproductive success. The Mississippi kite (Ictinia mississippiensis) is a species of regional conservation concern due to small population sizes and high rates of nest failure. We monitored Mississippi kite nests, documented causes of nest failure, and examined relationships between habitat features and predator-specific patterns in nest predation in a floodplain forest in east-central Arkansas. We identified Texas ratsnakes (Pantherophis obsoletus) and owls (Strigidae) as the dominant nest predators and predation by each was influenced by different habitat features. Ratsnake predation was greater in areas with fewer overstory trees and when kite nests were positioned farther above the tree canopy. Owls were more likely to depredate nests farther from the forest edge and nests that had less canopy coverage around them. Our results illustrate that the nest site characteristics preferred by kites reduce nest predation risk, indicating most of the management actions proposed to promote kite nesting are likely to create or maintain quality habitat for this species in the Mississippi Alluvial Valley. Beyond knowing the main causes of nest failure in kites, our results may also provide a glimpse into threats faced by mid-story and other canopy-nesting birds, a guild for which very little information exists regarding causes of nesting failure. © 2014 The Wildlife Society.

Mountain Biking Trail Use Affects Reproductive Success of Nesting Golden-Cheeked Warblers

We evaluated foraging and nesting behavior, territory size, and nest success of Golden-cheeked Warblers (Dendroica chrysoparia), a federally endangered songbird, relative to mountain biking trail use. We conducted our study at two mountain biking sites and two control sites at Fort Hood Military Base and in Austin, Texas, in spring 2002 and 2003. Territories of male Golden-cheeked Warblers in biking sites (2.2 ha) were >1.5 times as large as those in non-biking sites (1.4 ha). Mayfield nest success in biking sites (n = 33) was 35% compared to 70% in non-biking sites (n = 22). Nest abandonment was three times greater in biking areas (15%) than non-biking areas (5%). Seven nests were depredated in biking sites, but only two nests were depredated in non-biking sites. Texas rat snakes (Elaphe obsoleta) were the most frequent nest predator at biking sites, accounting for 71% of the predations. We conducted behavioral observations of male Golden-cheeked Warblers in biking (n = 139) and non-biking (n = 204) sites. Males spent similar amounts of time in diurnal behaviors in biking and non-biking sites. We used video-camera systems to record female nesting behaviors at 17 nests in biking sites and 15 nests in non-biking sites. Nesting behaviors of females did not differ between biking and non-biking sites. The cumulative effect of disturbance from mountain biking trail use on Golden-cheeked Warbler foraging and nesting behavior appears to be minimal, but fragmentation and alteration of habitat by mountain biking trails may reduce quality of nesting habitat for Golden-cheeked Warblers.

Ratsnakes and Brush Piles: Intended and Unintended Consequences of Improving Habitat for Wildlife?

Brush pile creation is a common habitat management method used to attract wildlife. However, there is a paucity of data regarding effectiveness of brush pile creation and the indirect effects of brush piles on multi-species interactions. Here we document use of man-made brush piles by Texas ratsnakes (Elaphe obsoleta), examine mechanisms behind that use, and present results of a pilot study comparing avian nest success in areas with and without brush piles to determine if predator attraction to brush piles negatively affects the surrounding bird community. Radio-tracked snakes were found in brush piles 10% of the time, despite brush piles comprising less than 0.2% of the habitat by area. More abundant small mammals and more moderate temperatures in brush piles than in surrounding habitats could explain snakes' attraction to brush piles. Nest success of birds was similar in areas with and without brush piles in the year following brush pile creation. Because it may take substantially longer than 1 y for snake use to reach its maximum, however, it is premature to conclude that brush piles do not affect birds nesting in adjacent habitat. Given the apparent prevalence of brush pile creation, and the demonstrated preference of brush piles by ratsnakes, further research to document the consequences of brush pile creation is warranted.

Texas Ratsnake Predation on Southern Flying Squirrels in Red-Cockaded Woodpecker Cavities

Elaphe spp. (ratsnakes) are frequent predators on cavity-nesting birds and other vertebrates, including Glaucomys volons (Southern Flying Squirrels). They are known predators of Picoides borealis (Red-cockaded Woodpeckers), especially during the nestling phase. Picoides borealis cavities are frequently occupied by Southern Flying Squirrels, often several squirrels per cavity. Behavioral aspects of ratsnake predation on flying squirrels in woodpecker cavities is an important component required for a full understanding of the potentially complex interaction between Red-cockaded Woodpeckers, Southern Flying Squirrels, and ratsnakes. We induced previously captured Elaphe obsoleta (Texas Ratsnake) to climb boles of pine trees and gain access to Red-cockaded Woodpecker cavities known to contain Southern Flying Squirrels, and observed the resulting predatory interactions. Eight of nine ratsnakes successfully captured 14 of 22 Southern Flying Squirrels present in the cavities.

Texas Ratsnake Predation on Southern Flying Squirrels in Red-Cockaded Woodpecker Cavities

Texas Ratsnake Predation on Southern Flying Squirrels in Red-Cockaded Woodpecker Cavities

Effects of parasitic infection and radio‐transmitters on condition, hematological characteristics and corticosterone concentrations in Texas ratsnakes

AbstractParasites are a health concern of many wildlife species, although their effect on reptiles is poorly studied. Here we examine effects of hemogregarine and external parasites on Texas ratsnake Elaphe obsoleta white blood cell (WBC) concentrations, WBC differentials, heterophil/lymphocyte ratios, packed cell volume (PCV), corticosterone concentrations and body condition. We found little evidence that either ectoparasites or hemogregarines affected the health of Texas ratsnakes. We found a seasonal increase in corticosterone, consistent with glucocorticoids priming the snakes to deal with higher predation risks later in the season. We also examined whether the potential stress of carrying a surgically implanted radio‐transmitter compounds any parasitic health effects. We found no effect of transmitters on most aspects of health. We did find equivocal evidence that WBC concentrations were higher in snakes with transmitters and that PCV decreased following transmitter implantation. Although our results generally support the view that data collected using radio‐telemetry are unlikely to be biased due to adverse health effects of transmitters, the growing importance of telemetry for studies of snakes and other taxa argues for further research on this topic. When possible, researchers should design telemetry studies in such a way that assessing potential heath effects of transmitters is one of the objectives.

Sex differences in behavior associated with sex‐biased mortality in an oviparous snake species

Sex differences in behavior associated with reproduction often result in sex‐biased mortality. Male‐biased mortality appears to be the prevalent pattern for birds and mammals, but recent work suggests that higher female mortality may be the norm for snakes, at least for viviparous species. Here we used radio‐telemetry to examine sex‐biased mortality in Texas ratsnakes Elaphe obsoleta, an oviparous species, and test the hypothesis that differences in behavior are associated with higher rates of mortality. Female ratsnakes had lower survival than male ratsnakes. For both sexes decreased survival was associated with higher activity and increased basking. Male ratsnakes were most active and basked most during the spring when mating occurred, which was when almost all male mortality occurred. Although female ratsnakes also moved and basked most during the mating season, they maintained relatively high levels of movement and basking through the summer and fall, and female mortality occurred throughout that period. Thus, contrary to the expectation that the cost of reproduction should be highest prior to egg laying for females of oviparous snakes, the mortality pattern documented here suggests the cost of reproduction is greatest following egg laying, similar to what has been found for females of viviparous species. As capital breeders (whether oviparous or viviparous), female snakes must rebuild energy reserves following a bout of reproduction, and the associated increase in foraging and basking required to do so increases female susceptibility to predation. Further studies are required to determine if female‐biased mortality is the norm in snakes and if so, to determine the demographic and life‐history consequences.

Does Prey Availability Determine Seasonal Patterns of Habitat Selection in Texas Ratsnakes

An animal's requirements (e.g., food vs. shelter) from its environment are likely to vary seasonally and, therefore, so too should habitat selection. Here, we test the hypothesis that Texas Ratsnakes (Elaphe obsoleta) choose habitats based on prey availability during their active season and on cover during winter. We examined snake habitat selection at three spatial scales and compared that to abundance of small mammals and nesting birds, which we confirmed by diet analysis to be the snakes' principal prey. Small mammal trapping and avian point counts showed that overall prey abundance was higher on mesas and slopes compared to savannahs. Compared to availability of habitats within the entire study area, snakes selected home ranges with a high proportion of slope habitat. Within home ranges, however, selection for slopes was exhibited only during winter when foraging is at a minimum and snakes are relatively inactive. Snakes did not use habitat within home ranges selectively during the active season or during the avian breeding season. The latter result suggests that ratsnakes are effective avian nest predators despite preying on birds opportunistically. However, it is also possible that some individual ratsnakes specialize on birds, whereas the majority preys on mammals. Microhabitat analysis comparing winter and active season sites showed that snakes preferentially used areas of high canopy cover and rock ground cover during winter. Collectively these results provide limited support for the hypothesis that ratsnakes use habitats based on prey availability but do indicate that ratsnakes select winter habitat based on cover availability.

Is nest predation on two endangered bird species higher in habitats preferred by snakes?

Higher predation on birds' nests is often associated with habitat fragmentation and edges, but little research has addressed whether these predation patterns result from non-random habitat use by predators. Using 2 endangered bird species, black-capped vireo (Vireo atricapilla) and golden-cheeked warbler (Dendroica chrysoparia), and their primary nest predator, the Texas ratsnake (Elaphe obsoleta), we test the hypothesis that birds nesting in habitats preferred by ratsnakes suffer higher nest predation than those nesting in non-preferred habitats. Ratsnakes did not use their habitat randomly, instead preferring locations with more structure and closer to cover objects and edges. Despite large sample sizes (186 nests and 31 snakes with radio transmitters), however, we did not find clear relationships between snake habitat preference and avian nest survival. Our results, in conjunction with those of another study, suggest that warbler nests were at greater risk if edge was abundant near the nest. Thus, reducing edge could promote nest survival. Additionally, because ratsnakes preferred warbler habitat over vireo habitat, vireos might suffer less predation in larger habitat patches that would increase average distances of nests from the snakes' preferred habitat. In making one bird species' habitat less attractive to ratsnakes, however, we may increase snake predation on other species.

PREY-MEDIATED EFFECTS OF DROUGHT ON CONDITION AND SURVIVAL OF A TERRESTRIAL SNAKE

Drought can have severe ecological effects and global climate-change theory predicts that droughts are likely to increase in frequency and severity. Therefore, it is important that we broaden our understanding of how drought affects not only individual species, but also multitrophic interactions. Here we document vegetation and small-mammal abundance and associated patterns of Texas ratsnake (Elaphe obsoleta) body condition and survival before, during, and after a drought in central Texas, USA. Vegetation (grass and forbs) height and small-mammal capture rates were two times greater in wet years compared to the drought year. The decline of small mammals (the snakes' principal prey) during the drought was associated with a drop in ratsnake body condition, consistent with reduced food intake. During the drought, snake mortality also increased 24%. Although higher snake mortality was attributable to predation and road mortality rather than being a direct result of starvation, an increase in risk-prone behavior by foraging snakes probably increased their exposure to those other mortality factors. Drought conditions lasted only for 21 months, and vegetation, small-mammal abundance, and snake condition had returned to pre-drought levels within a year. Although estimates of snake population size were not available, it is likely that substantially more than a year was required for the population to return to its previous size.

GOLDEN-CHEEKED WARBLER NEST MORTALITY AND PREDATORS IN URBAN AND RURAL LANDSCAPES

Abstract Predation is a major cause of nest failure for songbirds, yet information is lacking on the relative importance of predator species in different landscapes. We identified nest predators of Golden-cheeked Warblers (Dendroica chrysoparia) in an urban landscape, compared cause-specific mortality rates between urban and rural landscapes, and evaluated whether monitoring nests with cameras affected nest survival. We monitored 68 nests with cameras in Austin, Texas, during 2005, 2006, and 2008 to identify causes of mortality, including predators, in an urban landscape. The period mortality and predation rates were 0.60 (95% CI: 0.42–0.73) and 0.52 (95% CI: 0.37–0.68), respectively. We identified predators at 20 nests: Texas rat snakes (Elaphe obsoleta lindheimerii) depredated eight nests (40%), Western Scrub-Jays (Aphelocoma californica) depredated six (30%), Cooper's Hawks (Accipter cooperii) depredated two (10%), fox squirrels (Sciurus niger) depredated three (15%), and fire ants (Solenopsis sp.) dep...

Snake activity affects seasonal variation in nest predation risk for birds

Variation in predator behavior has been proposed, but not tested, as a mechanism producing seasonal declines in avian nest success. We test this hypothesis by documenting seasonal activity of Texas ratsnakes Elaphe obsoleta and nest failure of endangered black‐capped vireos Vireo atricapilla and golden‐cheeked warblers Dendroica chrysoparia on which the snakes prey. Nest survival analysis was based on 880 vireo and 228 warbler nests and 3,060 snake locations from 62 radio‐tracked snakes. Although nest success varied with snake activity for both birds, specific patterns differed substantially. Vireo daily nest survival was negatively correlated with snake activity over the three‐year study, despite substantial variation among years in weather, and the fact that these birds are almost certainly a minor prey species of the ratsnakes. Warblers exhibited less clear‐cut seasonal variation in nest success, and the association between nest success and snake activity was less pronounced than for vireos. Increased activity at warmer temperatures explained some of the seasonal change in snake movements, although mating may have accounted for a mid‐season peak in activity. These results indicate that variation in predator behavior can be associated with and potentially cause seasonal changes in nest success, but also that these relationships are species specific even within the same community and may depend on aspects of the nesting ecology of the prey such as nest site selection.

Use of Trees by the Texas Ratsnake (Elaphe obsoleta) in Eastern Texas

We present information on the use of trees by Elaphe obsoleta (Texas Ratsnake) in a mesic pine-hardwood forest in eastern Texas. Using radiotelemetry, seven snakes (3 females, 4 males) were relocated a total of 363 times from April 2004 to May 2005, resulting in 201 unique locations. Snakes selected trees containing cavities and used hardwoods and snags for a combined 95% of arboreal locations. Texas Ratsnake arboreal activity peaked during July and August, well after the peak of avian breeding activity, suggesting arboreal activity involves factors other than avian predation.

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.

Genetics of color mutations in the snake, Elaphe obsoleta

The following snakes were located and acquired: two albino black rat snakes; one xanthic black rat snake, one hypopigmented black rat snake with phenotype not previously described; one leucistic Texas rat snake, one F1 wild-type black rat snake heterozygous for albinism, and one male and two female F1 wild-type Texas rat snakes heterozygous for albinism. Between 1975 and 1983 these snakes were subjected to various breeding combinations to determine their genetics. The results of 29 matings are summarized. All of the aberrant phenotypes were found to be autosomal recessive mutations. Allelic and nonallelic forms of albinism were found to exist in the black rat snake. The xanthic form of hypopigmentation was found to be tyrosinase—positive partial albinism. Leucism in the Texas rat snake appears to be associated with bilateral exophthalmos in some instances. The previously undescribed black rat snake phenotype was designated “brindle” because of its appearance. It appears to be a genetically determined alteration in the quantity or quality of pigment, or both, and it does not undergo ontogenetic loss of pattern. It is not a form of tyrosinase-positive albinism analogous to the xanthic phenotype.

Texas Rat Snake Feeds on Mexican Freetail Bat and Wood Duck Eggs

Texas Rat Snake Feeds on Mexican Freetail Bat and Wood Duck Eggs

Scanning electron microscopy and distribution of specialized mechanoreceptors in the texas rat snake, Elaphe obsoleta lindheimeri (Baird and Girard).

Scanning electron microscopy (SEM) of the surface tubercles of a specialized mechanoreceptor found within the head of Elaphe obsoleta lindheimeri indicates that the tubercle consists of a craterlike structure with a peg emerging from its center. After removal of the outer keratinized layers of the epidermis, the SEM discloses a replicate tubercle on the underlying alpha keratin layer. Over 6000 tubercles were found within a single snake. The mechanoreceptors were more densely concentrated on anterior scales, and their number appears to be species specific so that they are more concentrated in snakes with smaller heads than in those with larger ones.