HR44(2)213-215DOrgeix (1)

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Herpetological Review, 2013, 44(2), 213–215.© 2013 by Society for the Study of Amphibians and Reptiles

Northern Mexican Gartersnakes, Thamnophis eques megalops, feeding on Spea multiplicata in an Ephemeral Pond

The Northern Mexican Gartersnake, Thamnophis eques megalops, is the only subspecies of the Mexican Gartersnake oc-curring in the United States. Historically, it ranged from central Arizona and southwestern New Mexico southward through the Mexican states of Sonora, Chihauhua, Durango, Guanajuato, Hi-dalgo, and San Luis Potosí (Brennan and Holycross 2006; Rosen and Schwalbe 1988; Rosen et al. 2002), but is now thought to be at extremely low population densities or extirpated in New Mexico (Holycross et al. 2006). In Arizona, population declines have been recorded in approximately 83% (15/18) of the Mexican Garter-snake populations originally surveyed in the early to mid-1980s and re-surveyed in 1995–2000 (Rosen et al. 2002). Survey data from the Gila River watershed in Arizona and New Mexico during 2004–2005 suggest continued severe population declines and lo-cal extirpations (Holycross et al. 2006). These declines were con-sidered significant enough that the Center for Biological Diver-sity petitioned (CBD) to list the Northern Mexican Gartersnake as Threatened or Endangered under the U.S. Endangered Species Act (CBD 2003). Although the petition was initially unsuccessful (USFWS 2006), the U.S. Fish and Wildlife Service (USFWS) later concluded that the Northern Mexican Gartersnake is threatened with extirpation, or may already be extirpated from 85–95% of its historical distribution in the United States and that listing was warranted (USFWS 2008). The USFWS expects to publish updat-ed information in the Federal Register on the status of Northern Mexican Gartersnakes (J. M. Servoss, pers. comm.)

Northern Mexican Gartersnakes are associated with perma-nent water and cienega habitats containing aquatic vegetation and a wide range of terrestrial vegetation (Rosen and Schwalbe 1988; Rossman et al. 1996). Their prey consists primarily of fish, frogs and tadpoles, although invertebrates, lizards (T. R. Jones, pers. comm.), and mammals are also eaten (Garcia and Drum-mond 1988; Rosen and Schwalbe 1988; Van Devender and Lowe 1977).

Observations.—On 15 July 2012 at 2130 h following one of the first heavy monsoon rains in the area, a male Mexican Gar-tersnake was observed feeding on a Mexican Spadefoot (Spea multiplicata) in a seasonal pond at the Appleton-Whittell Re-search Ranch (AWRR) of the National Audubon Society, near Elgin, Arizona, USA. The pond, which had been dry since the summer of 2010 (R. Cogan, L. Kennedy, pers. comm.), filled earlier that day to approximately 150 × 30 × .5 m (L×W×D) from overflow of an adjacent dry wash which had also been dry since the previous summer (Fig. 1). A breeding aggregation (>50) of S. multiplicata, that had not been present on previous nights, was active in the tank. The 520 mm SVL snake was captured by hand, photographed, and released on site. The following morn-ing during 0745–0950 h, five other Mexican Gartersnakes were observed basking at the bases of Sacaton grass (Sporobolus wrightii) surrounding the pond. Four were captured by hand, but the fifth eluded capture. The captured snakes included two males (505 mm, 520 mm SVL) and two females (675 mm, 737 mm SVL). The snakes were released at their site of capture fol-lowing data collection. All five snakes captured were at or near sexual maturity. Male Mexican Gartersnakes from nearby Finley Tank, also at AWRR, are thought to reach sexual maturity when

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CHRISTIAN A. D’ORGEIX1*

TOM MATHIES2

BROOKE L. ELLISON1 KELSEY L. JOHNSON1

IVAN V. MONAGAN1

TODD A. YOUNG1

1 Department of Biology, Virginia State University, Petersburg, Virginia 23806, USA

2Genesis Laboratories, Inc., PO Box 1195, Wellington, Colorado 80549, USA *Corresponding author; e-mail: [email protected]

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they are 410–580 mm SVL; females at SVL’s between 550–700 mm (Rosen and Schwalbe 1988).

The four snakes captured on the morning of 16 July were engorged with anurans (Fig. 2). One female regurgitated seven S. multiplicata upon capture and palpation revealed two more. The seven regurgitated spadefoots, one female and six males, had a combined mass of 60 g (Fig. 3). The approximate mass of all nine spadefoots ingested by the snake was 77 g, representing approximately 39% of the total mass of the 200 g snake, recorded after she had re-ingested all seven of the regurgitated prey. No feeding or aquatic activity was observed during the morning of 16 July, indicating that the snakes had fed during the previous night or in the early morning hours prior to the initial sighting of two snakes basking at 0745 h.

Discussion.—To our knowledge, this is the first documenta-tion of Mexican Gartersnakes feeding on any species of spade-foot and the first report of nocturnal foraging in this species. In contrast to reports stating that Mexican Gartersnakes are restricted to riparian habitats with permanent sources of water (Brennan and Holycross 2006; Rosen and Schwalbe 1988; Ross-man et al. 1996), our observations raise the possibility that this species can occur, at least temporarily, in riparian areas where standing water is only seasonally available. In a study of Mexican Gartersnakes at Finley Tank in 2007, two neonates were found at the tank in July, the beginning of the monsoons, which had been dry since the previous winter, suggesting at least one adult female had successfully reproduced without access to a nearby permanent water source containing frogs or fish (d’Orgeix 2011).

The species is either extirpated or occurs at extremely low densities at the Babacomari River, which is the nearest large permanent water source 4.2 km N and downstream from the pond, and none has been seen since 2007 in a small rock pool in Post Canyon 1.5 km SW of the pond (d’Orgeix 2011). The near-est known population of Mexican Gartersnakes is 1.2 km distant at Finley Tank where individuals have been seen as recently as 2009 (d’Orgeix 2011). Although Finley Tank was once a perma-nent water source, it has contained water only intermittently since 2006 (d’Orgeix 2011). Following the July–August monsoons in 2011, Finley Tank went dry and did not fill again until the night we observed snakes in the pond. If the snakes we observed had emigrated from Finley Tank between the time of the pond filling and our observations, they would have had to have left Finley Tank as it was filling with rainwater and moved 1.2 km overland through open semi-desert grassland in 6–17 h. Even less plausi-bly, snakes could have followed the single connecting riparian corridor from Finley Tank to the pond (~2.3 km long) that would have required upstream travel against rapidly moving floodwa-ters carrying substantial debris. Last, none of the five snakes we captured at the pond were marked individuals from the Finley Tank population where all individuals encountered (N = 29) had been given unique identification marks and PIT tags from 2007 to 2009 although recapture rates were low (d’Orgeix 2011). These considerations collectively suggest that the snakes we observed were already present in the near vicinity of the pond before it filled.

Our observations raise the possibility that, under drought conditions, spadefoots are an important food source for Mexican Gartersnakes, and are taken during the brief time these anurans are breeding in ephemeral ponds. Snakes may then be aestivat-ing when the pond is dry. Aestivation in snakes has rarely been documented, but the small aquatic snake Seminatrix pygaea aestivates in seasonally dry wetland and has been predicted to

fig. 1. Ephemeral pond at the National Audubon Society Appleton-Whittell Research Ranch, Santa Cruz County, Arizona. Northern Mexican Gartersnakes, Thamnophis eques megalops, were observed basking at the bases of Sacaton grass, Sporobolus wrightii, in the left foreground and left rear shore of the pond.

fig. 2. A Northern Mexican Gartersnake engorged on Mexican Spade-foots, Spea multiplicata, at the National Audubon Society Appleton-Whittell Research Ranch, Santa Cruz County, Arizona.

fig. 3. Seven Mexican Spadefoots, Spea multiplicata, regurgitated by a female Northern Mexican Gartersnake, Thamnophis eques mega-lops, upon her capture at the National Audubon Society Appleton-Whittell Research Ranch, Santa Cruz County, Arizona. Toads were re-ingested by the snake prior to her release at the site of capture.

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survive multiyear droughts in this manner (Winne et al. 2006). However, we cannot exclude the possibility that the snakes are also feeding on other terrestrial organisms (e.g., lizards, rodents) when ephemeral sites are dry, or emigrating to other sites with permanent water.

To confirm whether our findings are more widely applicable to the ecology of Mexican Gartersnakes, additional surveys for snakes are needed at ephemeral sites in riparian habitat when spadefoots are breeding. Subsequent results may determine whether use of this previously unrecognized habitat and food source is more prevalent than previously thought and contribute meaningfully to recovery strategies.

Acknowledgments.—We thank Tom Jones, Joe Mitchell, Jeff Ser-voss, and two anonymous reviewers for providing comments and suggestions that improved this manuscript. Linda Kennedy and Roger Cogan at the National Audubon Society Appleton-Whittell Re-search Ranch provided plant identification data and pond measure-ments in addition to providing logistic support. This research was partially funded through a grant from the National Science Founda-tion under HBCU-UP (HRD-1036286) to C. d'Orgeix. Reasearch was conducted under an Arizona Game and Fish Department Scientific Collecting permit #566344. All applicable institutional animal care guidelines were followed.

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Behavior of Plethodon metcalfi Following Anesthetization with Tricaine Methanesulfonate (MS-222)

Tricaine methanesulfonate (also called Ethyl 3-aminobenzo-ate methanesulfonic acid or MS-222) is commonly used as an anesthetic in fish and amphibian research. Because MS-222 gen-erally appears to be safe and effective for a range of amphibian species, it is commonly used in the process of surgery or mark-ing of animals (e.g., Chelgren et al. 2006; Osbourn et al. 2011; Peterman et al. 2008). Amphibian responses to anesthesia may be species-specific (Fellers et al. 1994), and a number of studies have performed multi-species evaluations of induction and re-covery times (Cecala et al. 2007; Lowe 2004; Peterman and Sem-litsch 2006). Recovery times of individuals following anesthesia have previously been reported as the time until first response to a stimulus (Cecala et al. 2007; Peterman and Semlitsch 2006), re-covery of a righting reflex (Crook and Whiteman 2006), or recov-ery of normal motor function with no indication of sluggishness or disorientation (Cecala et al. 2007; Crook and Whiteman 2006). In many cases, researchers will face a trade-off between the de-sire to minimize the time that animals are in captivity and the need to ensure that animals have adequate time to recover from anesthesia before release.

As a practical consideration for field research, allowing am-phibians adequate time to recover from anesthesia may be criti-cal for ensuring that our research activities do not cause preda-tion or desiccation-related mortality. Behavioral studies are also conducted on the assumption that released individuals are behaving normally between subsequent observations. Further-more, many mark-recapture models for estimating population parameters are based on the assumption that all individuals in

KATHLEEN M. DIPPLEDepartment of Biology, Appalachian State University, Boone, North Carolina 28608, USAGRANT M. CONNETTE*Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211, USARAYMOND D. SEMLITSCHDivision of Biological Sciences, University of Missouri, Columbia, Missouri 65211, USA

* Corresponding author; e-mail: [email protected]