Narrow-headed gartersnake

Thamnophis rufipunctatus

Identification

Narrow-headed gartersnakes are perhaps the easiest to differentiate among the five gartersnake species in Arizona. These snakes have a reddish brown, charcoal, tan, or olive background color, with paired red, reddish brown, dark brown, or grey blotches on the back (after Brennan and Holycross 2006, Fowlie 1965). In both adults and juveniles, these blotches tend to be more obvious near the head and fade toward the tail. The belly is lighter colored, often yellowish or greenish, and may have dark irregular markings. Younger snakes have more striking markings, while older adults lose their pattern. Snakes in certain populations, e.g. the Black River (see cover image) may be melanistic; others may be very light-colored, almost green, with red spots; and still others may be almost uniformly red with faint spots. Individuals from within the same litter may exhibit different color morphs (normal brown or red).

The most striking feature of the species, however, is the long, narrow snout, resulting in a decidedly pointed facial appearance. This feature is also evident in whole shed skins found in the water; with practice narrow-headed gartersnake shed skins may be distinguished from other species by the lack of obvious pattern, and by the long, pointed snout in front of the eye shields. Adult female narrow-headed gartersnakes can reach 44 inches in length (1,115 mm; Brennan and Holycross 2006); newborns are slightly larger and thicker than a No. 2 pencil.

Similar species include the spotted, non-striped morph of the wandering gartersnake. The two species may be differentiated by snout length and shape. Also, wandering gartersnake blotches tend to resemble regularly spaced square dots, whereas narrow-headed gartersnake blotches are typically more rounded and irregular, and may touch each other.

Status & distribution

The narrow-headed gartersnake (Thamnophis rufipunctatus) is a federally-threatened riparian-obligate snake (US Fish and Wildlife Service [USFWS] 2014). Critical habitat for this sensitive species has been proposed but not yet finalized (USFWS 2013). This species is protected under Arizona Game and Fish Department Commission Order 43 (Reptiles): no collection, harassment or harming, hunting, trapping, or capture is allowed without special permits (Arizona Game and Fish Department 2011a).

The species is found in the Southwestern United States; a closely related species, the Madrean narrow-headed gartersnake, T. unilabialis, occurs in the Sierra Madre Occidental of northwestern Mexico (Tanner 1990, Wood et al. 2011). Disjunct (widely scattered) populations occur in fast-flowing higher-elevation (typically at 3937 – 6233 feet [1200-1900 m] elevation) headwater streams near and below the Mogollon Rim in Arizona and New Mexico (Degenhardt et al. 1996, Holycross and Brennan 2006, Wood et al. 2011, Emmons and Nowak 2012; reviewed in USFWS 2014).The range of the Narrow-headed Gartersnake has decreased to the point where populations have become ecologically and genetically isolated (Wood et al. 2011; unpubl. data), and currently five or fewer historic localities are thought to contain “likely viable” populations (USFWS 2014).

Ecology

Narrow-headed gartersnakes are highly aquatic, fish-eating specialists occupying a water snake niche (Hibbitts and Fitzgerald 2005); in fact at various times taxonomists have placed them in the water snake (Nerodia) genus (Rossman et al. 1996a, Crother et al. 2008).

The hibernation period for telemetered narrow-headed gartersnakes in Oak Creek Canyon, Arizona (2004-2006) began between late October and late November, and lasted until early to late March (Nowak 2006). Telemetered snakes were not observed active at or outside of hibernation sites during the winter. Hibernation sites generally appeared to be above the 100-year floodplain, and included rock outcrops (30-200m from water’s edge), rocky slopes above the creek, and rock piles.

Though active on land, telemetered narrow-headed gartersnakes did not appear to enter the water on a regular basis before mid-May, likely due to creek temperatures being too cold (11.5°C on May 1; Nowak 2006). Less than ¼ of the telemetered snake observations during the active season were in the water, but most snakes were found within 100 m of water’s edge (Nowak 2006). The mating season is presumed to be in the spring and early summer, with 8-18 young typically born from July to August (Rossman et al. 1996a, Brennan and Holycross 2006). Gartersnakes give birth to their young, and develop a kind of placentation during pregnancy, presumably with some ability to convey nutrients to, and wastes from, embryos (e.g. Blackburn and Lorenz 2003, Thompson and Speak 2003).

Primary prey items are native fish (especially suckers, dace, and trout), soft-rayed non-native fish (e.g. trout and mosquitofish Gambusia affinis; Nowak and Santana-Bendix 2002, Hibbitts et al. 2009; Jennings and Christman 2010). While historic records also include tadpoles (e.g. Ranid frogs, Lithobates spp. and tree frogs, Hyla spp.) and tiger salamanders (Ambystoma tigrinum), these are likely based primarily on captive records and may not represent normal wild diets (USFWS 2014). Narrow-headed gartersnakes have several derived morphological features (e.g. a long, pointed snout and eyes forward on the head) thought to be adaptations to capturing fish prey underwater (Hibbitts and Fitzgerald 2005). When compared to two other gartersnakes in a laboratory setting, narrow-headed gartersnakes consistently foraged on the bottom of the water column, whereas the other species very rarely or never took fish near the bottom of the experimental tank (de Queiroz 2003).

These laboratory observations are directly relevant to field surveys for narrow-headed gartersnakes: individuals of all age classes are often found underwater, including under rocks or debris, in woody debris in pools, in bedrock channels, underneath riffles, or simply crawling along the stream bottom (Nowak and Santana-Bendix 2002, Nowak 2006, Jennings and Christman 2010). They may also be found swimming on the surface of the water, or perched in willows, fountain-shaped sedges (Carex sp.), or other vegetation above the water (presumably to watch for fish), or basking on vegetation or under bark near the water (Rosen and Schwalbe 1988, Nowak and Santana-Bendix 2002, Holycross et al. 2006). When alarmed, narrow-headed gartersnakes near water typically flee quickly into the water and dive under large boulders. As ectotherms with low metabolic rates, they appear capable of holding their breath for several to tens of minutes (Nowak, pers. obs.); however, more research is needed to determine both duration and the physiological processes that allow long-term breath-holding. Away from water (e.g. while basking, shedding, or while females are pregnant), narrow-headed gartersnakes often hide under large boulders, in rock talus, or in burrows under vegetation (Nowak 2006, Jennings and Christman 2010).

Threats

Narrow-headed gartersnakes have suffered extensive population declines throughout their ranges in the United States (Holycross et al. 2006, Hibbitts et al. 2009, USFWS 2014). Surveys in Arizona and New Mexico indicate that many declines have occurred within the last two decades (Rosen and Schwalbe 1988, Nowak and Santana-Bendix 2002, Holycross et al. 2006, USFWS 2014, Nowak and Drost 2015).

Threats include introduced non-native predators (e.g. fish, bullfrogs Lithobates catesbeianus, and crayfish Orconectes virilis), disappearance of native fish and amphibian prey, and loss or degradation of habitat (Rosen and Schwalbe 1988, 2002; Nowak and Santana-Bendix 2002; Holycross et al. 2006; Hibbitts et al. 2009, USFWS 2014). Factors such as disease, siltation (resulting in loss of foraging habitat) and loss of fish fauna after catastrophic fires, human predation, intense recreation pressure causing loss of near-shore habitat, and overgrazing are also suspected or hypothesized as reasons for decline in some areas (Nowak and Santana-Bendix 2002, Hibbitts et al. 2009, USFWS 2014, Nowak and Drost 2015; P. Rosen, pers. comm.). Recent apparent range expansions in native predator populations, such as otters (Lontra canadensis, Nowak, unpubl. data) and common black hawks (Buteogallus anthracinus, Etzel 2010), may also have impacts on populations of these gartersnakes that are already reduced by other factors; however these potential effects have not been studied. It is likely that no one factor has resulted in declines, but rather combinations of factors may act synergistically to cause declines.

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