Pantherophis obsoletus - (Say, 1823)
Western Ratsnake
Other English Common Names: Texas Ratsnake, Western Rat Snake, western ratsnake
Synonym(s): Elaphe obsoleta (Say, 1823) ;Pantherophis obsoleta (Say, 1823)
Taxonomic Status: Accepted
Related ITIS Name(s): Elaphe obsoleta (Say in James, 1823) (TSN 174177)
Unique Identifier: ELEMENT_GLOBAL.2.840332
Element Code: ARADB13030
Informal Taxonomy: Animals, Vertebrates - Reptiles - Snakes
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Reptilia Squamata Colubridae Pantherophis
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Concept Reference
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Concept Reference: Burbrink, F. T. 2001. Systematics of the eastern ratsnake complex (Elaphe obsoleta). Herpetological Monographs 15:1-53.
Concept Reference Code: A01BUR01NAUS
Name Used in Concept Reference: Pantherophis obsoleta
Taxonomic Comments: Burbrink et al. (2000) and Burbrink (2001) examined genetic and morphological variation in Elaphe obsoleta and determined that the nominal subspecies do not represent evolutionary lineages and should no longer be recognized. Further, these authors identified three clades within E. obsoleta, corresponding to populations (1) west of the Mississippi River (western clade), (2) east of the Mississippi River and west of the Appalachian Mountains and Apalachicola River (central clade), and (3) east of the Appalachians and the Apalachicola River (eastern clade). Burbrink (2000) recognized the three clades as distinct species: E. obsoleta (western clade), E. spiloides (central clade), and E. alleghaniensis (eastern clade). In mapping the distribution of the species, Burbrink indicated a very large area of "taxonomic uncertainty" extending from New England to northern Georgia. In this region the distribution of E. alleghaniensis was deemed "somewhat questionable with regard to hybridization with members of Elaphe spiloides." Although Burbrink concluded that the molecular data show that E. alleghaniensis and E. spiloides represent independently evolving units with separate evolutionary histories and thus should be recognized as different species under the evolutionary species concept, contact zones were not critically examined, so the nature and dimensions of clade boundaries, and the precise distributions of alleghaniensis and spiloides along the length of the Appalachians, remain uncertain. Jensen et al. (2008) mentioned Burbrink's proposed split but did not adopt it.

Molecular data indicate that Elaphe obsoleta lindheimeri, E. o. quadrivittata, and E. o. rossalleni are not distinct evolutionary lineages (Burbrink et al. 2000). The checklists by Crother et al. (2003) and Crother (2008) did not accept lindheimeri, quadrivittata, or rossalleni as valid taxa.

Elaphe bairdi, confirmed as a valid species by Burbrink (2001), was included in Elaphe obsoleta by some authors in older literature.

Utiger et al. (2002) examined mtDNA variation in New World and Old World "Elaphe" and determined that North American rat snakes currently included in the genus Elaphe form a monophyletic limeage that is distinct from Old World snakes that also have been regarded as Elaphe. They resurrected the genus Pantherophis for the rat snakes north of Mexico, including the following species: Pantherophis obsoletus (and P. alleghaniensis and P. spiloides, if one recognizes those taxa as species), P. guttatus, P. emoryi, P. vulpinus, P. gloydi, and P. bairdi. Based on mtDNA and nuclear DNA data, Burbrink and Lawson (2007) determined that New World Elaphe are not closely related to Old World Elaphe. Here we follow these studies and Crother (2008) and transfer New World Elaphe to the genus Pantherophis.
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 18Apr2016
Global Status Last Changed: 16Nov2001
Ranking Methodology Used: Ranked by calculator
Rounded Global Status: G5 - Secure
Reasons: Large range and many collection sites and locations in central North America; can be common in altered rural habitats; presumed large population size; likely relatively stable or slowly declining; no known major threats.
Nation: United States
National Status: N5 (06Nov2001)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Arkansas (S5), Iowa (S4), Kansas (S5), Louisiana (S5), Minnesota (S2), Missouri (S5), Nebraska (S4), Oklahoma (S5), Texas (S5)

Other Statuses

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent: 200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Range Extent Comments: As defined by Burbrink (2001), this species occurs west of the Mississippi River, from southern Louisiana along the Gulf Coast to southern Texas, west to central Texas on the Edwards Plateau, and northwward through Oklahoma, central and eastern Kansas, southeastern Nebraska, and southeastern Iowa to extreme southeastern Minnesota.

Area of Occupancy:  
Area of Occupancy Comments: Area of occupancy is known but very large.

Number of Occurrences:  
Number of Occurrences Comments: The number of distinct occurrences has not been determined using consistent criteria, but this species is represented by a very large number of collection sites and locations (as defined by IUCN).

Population Size: 100,000 to >1,000,000 individuals
Population Size Comments: Total adult population size is unknown but very large (presumably exceeds 100,000) This species is locally common in much of its range.

Overall Threat Impact: Low
Overall Threat Impact Comments: Intensive agricultural development and urbanization likely have caused localized declines, and collectors probably have depleted some easily accessible populations, but in most areas this snake is not threatened by these factors. As of 2016, this species was not known to be significantly affected by snake fungal disease.

Short-term Trend: Decline of <30% to relatively stable
Short-term Trend Comments: Trend over the past 10 years or three generations is uncertain, but extent of occurrence, area of occupancy, number of subpopulations, and population size probably have been relatively stable or slowly declining.

Other NatureServe Conservation Status Information

Distribution
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Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) As defined by Burbrink (2001), this species occurs west of the Mississippi River, from southern Louisiana along the Gulf Coast to southern Texas, west to central Texas on the Edwards Plateau, and northwward through Oklahoma, central and eastern Kansas, southeastern Nebraska, and southeastern Iowa to extreme southeastern Minnesota.

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: endemic to a single nation

U.S. & Canada State/Province Distribution
United States AR, IA, KS, LA, MN, MO, NE, OK, TX

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
IA Dubuque (19061)
MN Fillmore (27045), Houston (27055)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
07 Root (07040008)+, Coon-Yellow (07060001)+, Upper Iowa (07060002)+, Apple-Plum (07060005)+, Maquoketa (07060006)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Reproduction Comments: Lays clutch of 5-30 eggs, late June or July in Kansas. Eggs hatch August-October. May lay two clutches annually in south. May lay eggs in communal nest. Sexually mature in 4th year (Fitch 1970).
Ecology Comments: Red-tailed hawk is an important predator in Kansas (Fitch 1963).
Non-Migrant: Y
Locally Migrant: Y
Long Distance Migrant: N
Mobility and Migration Comments: Home range size is typically 12 ha or more in south (Tennant 1984), up to about 12 ha in Kansas (Fitch 1963). Home range averaged 5.6 ha (up to 13.4 ha) in Arkansas (Mullin et al. 2000).
Palustrine Habitat(s): FORESTED WETLAND, Riparian
Terrestrial Habitat(s): Bare rock/talus/scree, Cliff, Cropland/hedgerow, Forest - Conifer, Forest - Hardwood, Forest - Mixed, Old field, Savanna, Suburban/orchard, Woodland - Conifer, Woodland - Hardwood, Woodland - Mixed
Special Habitat Factors: Burrowing in or using soil, Fallen log/debris, Standing snag/hollow tree
Habitat Comments: Habitats include hardwood forest and woodland, wooded canyons, swamps, rocky timbered upland, wooded areas of streams and rivers, farmland near woods, old fields, barnyards, and rural buildings in wooded areas. These snakes often occur where wooded and open habitats (such as fields or farmland) are intermixed. They often climb trees, especially rough-barked species or those with vines, and they sometimes enter water. Hibernation sites are in deep crevices or underground.
Adult Food Habits: Carnivore
Immature Food Habits: Carnivore
Food Comments: Diet includes birds and their eggs, small mammals, lizards, frogs, and invertebrates; adults eat mainly endotherms while young eat mainly ectotherms.
Adult Phenology: Crepuscular, Diurnal, Hibernates/aestivates, Nocturnal
Immature Phenology: Crepuscular, Diurnal, Hibernates/aestivates, Nocturnal
Phenology Comments: Diurnal in spring and fall, nocturnal in summer (Behler and King 1979). Active late April to October in north, presumably longer in south.
Length: 257 centimeters
Economic Attributes Not yet assessed
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Management Summary Not yet assessed
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Population/Occurrence Delineation
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Group Name: Medium And Large Colubrid Snakes

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals (including eggs) in or near appropriate habitat where the species is presumed to be established and breeding.
Separation Barriers: Busy highway or highway with obstructions such that snakes rarely if ever cross successfully; major river, lake, pond, or deep marsh (this barrier pertains only to upland species and does not apply to aquatic or wetland snakes); densely urbanized area dominated by buildings and pavement.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 10 km
Separation Justification: Available information on movements of colubrid snakes is limited to a small minority of species. These data indicate that nearly all species have home ranges smaller or much smaller than 25 ha (e.g., less than 3 ha, Pituophis catenifer in California, Rodriguez-Robles 2003), with some up to about 75 ha (Heterodon platirhinos, average 50 ha, Plummer and Mills 2000), and the largest up to 225 ha in the biggest colubrids (Drymarchon, summer mean 50-100 ha, USFWS 1998).

Radiotelemetry data for Pantherophis indicate that residents of hibernacula that are 1-2 km apart (with suitable intervening habitat) probably interbreed (Prior et al. 1997, Blouin-Demers and Weatherhead 2002). However, "evidence of genetic structure even over short distances (e.g., 2-20 km) implies that gene flow among rat snake populations can be easily disrupted" (Prior et al. 1997). Loughheed et al. (1999) found evidence of substantial genetic exchange among local hibernacula (< 6 km apart), but gene flow over distances of 10s of km appears to be substantially less. Based on extensive radio-tracking data, Blouin-Demers and Weatherhead (2002) found that home range size of Pantherophis averaged 18.5 ha and ranged up to 93 ha; based on the most mobile individuals, Pantherophis from hibernacula up to 8 km apart can come together for mating. Pantherophis and probably other colubrids exhibit high fidelity to hibernacula and shift even to nearby sites only rarely (Prior et al. 2001).

Many of the several studies that report small home ranges for colubrids did not employ methods (e.g., radio telemetry) suitable for detecting full annual or multi-annual home range size, dispersal, or other long-distance movements, so these may have yielded underestimates of home ranges or activity areas.

At least some colubrids, including medium-sized species such as garter snakes, not uncommonly move between areas up to a few kilometers apart, and several species make extensive movements of up to several kilometers, so separation distances of 1-2 km for suitable habitat are too small for medium-sized and large colubrids.

A separation distance of 10 km for suitable habitat was selected as most appropriate for snakes assigned to this Specs Group because it seems generally unlikely that two locations separated by less than 10 km of suitable habitat would represent distinct occurrences.

For the purposes of these occurrence specifications, upland habitat is regarded as unsuitable habitat for aquatic and wetland snakes. For upland snakes, shallow or patchy wetlands are treated as unsuitable habitat whereas large deepwater habitats (subjective determination) are barriers.

Inferred Minimum Extent of Habitat Use (when actual extent is unknown): .5 km
Date: 12Feb2013
Author: Hammerson, G.
Notes: Separation distance for suitable habitat was changed from 5 km to 10 km based on comments from Dale Jackson (12 Feb 2013).
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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Element Ecology & Life History Edition Date: 18Apr2016
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

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