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Home , Cerastes (genus), Cerastes cerastes, Crotalus, Crotalus cerastes

Herpetology Notes, volume 12: 453-455 (2019) (published online on 01 May 2019)

Density, recapture probability, biomass, productivity, and population structure of Sidewinders ( ) in the Sonoran of

Daniel J. Leavitt1,* and Ashley A. Grimsley2

In the of the American Southwest, of Yuma (32.4502°N, 114.5770°E) and the other on Hallowell, 1854 occupies an the Barry M. Goldwater Range (BMGR; 32.4740°N, important role as a predator. Known as the sidewinder, 114.4653°E). Surveys were conducted on two five-day this psammophilous moves across the sand in sessions (with two days off between sessions) resulting a sinusoidal fashion (Secor et al., 1992). It is a well- in ten “capture occasions” (i.e., survey visits) per plot. camouflaged sit-and-wait predator and one of the A capture occasion was defined as the completion of smallest desert viperids in North America (Campbell one entire plot search, conducted by five to seven and Lamar, 2004). The feeds primarily on surveyors with teams of two to four observers covering and less frequently on small mammals, , 4.5 ha (half the 9-ha survey plot). Surveyors searched and other (Webber et al., 2016). When describing the plot on foot by spacing observers 18–25 m apart and the species from the in , walking in a serpentine fashion along transects for the Hallowell (1854) remarked that it “occurs in large length of the plot. numbers” and “is also seen in the Desert of , When encountered, snakes were captured by gently but is much less abundant”. Density estimates in the restraining them with snake tongs and employing an Kelso Dunes in the Mojave Desert ranged between 0.29 acrylic tube (Midwest Tongs, Greenwood, Missouri, and 0.71 snakes per hectare (Brown, 1970; Brown and USA). The snout–vent length (SVL) was measured on Lillywhite, 1992). Greene (1997) reported “estimates of each specimen using a measuring tape (Keson, Aurora, individuals per hectare are < 1”, presumably referring Illinois, USA) and specimens were weighed using a to the Mojave Desert. During the summer of 2015, we spring scale (Pesola, Schindellegi, Switzerland). All C. had an opportunity to conduct intensive sampling on C. cerastes captured for the first time were marked with cerastes in the Sonoran Desert of Yuma County, Arizona, a unique number on the side of their body using black USA. The objective of this work was to gather baseline indelible ink markers for rapid visual identification demographic data on C. cerastes. Specifically, we were in the event of repeated detections during the same interested in estimating density, recapture probability, season. Markings allowed us to know if the snake had and biomass, as well as insights into population structure already been tagged, thereby avoiding additional stress of this snake species in the Sonoran Desert. to the snake. All C. cerastes of sizes > 180 mm were From 17–28 August 2015 and 14–25 September 2015 PIT-tagged with HPT 8 tags using disposable MK 165 we surveyed two rectangular 9-hectare (ha) plots 12 implanters (Biomark, Boise, , USA). Sex was km apart in Yuma County, Arizona. One of these was determined by inserting a small probe (Midwest Tongs, located on Bureau of Reclamation (BOR) lands south Greenwood, Missouri, USA) into the cloacal opening to detect hemipenial pockets (in males) or anal scent glands (in females) by observing the depth to which the probe could be inserted. Age was determined as either young-of-year or adult based on SVL (Reiserer, 2001). 1 Resources Management and Planning Branch, Naval Air To investigate the population dynamics of C. cerastes, Weapons Station, China Lake, California 93555, USA. 2 Arizona Game and Fish Department, 5000 West Carefree we summarized data for each plot separately, as well as Highway, Phoenix, Arizona 85086, USA. for both plots combined. We estimated density by two * Corresponding author. E-mail: [email protected] means; one included a direct calculation, dividing the 454 Daniel J. Leavitt & Ashley A. Grimsley number of snakes per number of hectares of the plot with 20 and 21 juveniles captured at BMGR and BOR, for adults and juveniles. We also conducted a closed- respectively. Fewer recaptures occurred at BMGR (n = capture Huggins model in Program MARK (White and 3) than at BOR (n = 6). Adult SVL averaged 510.6 mm Burnham, 1999) to estimate adult density and capture/ with a range of 431–647 mm, and females (mean SVL recapture probabilities. We built a set of models that 526.0 mm) were larger than males (mean SVL 487.5 examined different sources of heterogeneity including mm). Juvenile SVL averaged 211.6 mm with a range of temporal, behavioural, and individual heterogeneity 175–275 mm. Adult mass averaged 185.0 g and females to evaluate these populations (Otis et al., 1978). To were on average slightly heavier (193.1 g) than males determine which of these models was the best fit, (172.1 g). Juvenile mass averaged 7.0 g. Analysed by we compared AICc values (Burnham and Anderson, study plot, the observed biomass of snakes was slightly 2003). To estimate the biomass of C. cerastes, we first higher at BMGR (2.03 kg) than at BOR (1.96 kg). With aggregated adult and juvenile snake mass data per plot corrections for area this equals 0.22 kg/ha and 0.23 kg/ after removing recaptured individuals. We calculated ha for BOR and BMGR, respectively. average values for adult and juvenile snakes and then The model that best explained adult population multiplied the density estimates per age group to the densities and had the lowest AICc value accounted for average biomass estimates for each group. To estimate differences between plots and suggested differences in productivity, we compared total number of juvenile C. behaviour after initial capture (Table 1). The model that cerastes by plot. Population structure was described best explained juvenile density indicated differences by evaluating the number of adults to juveniles and by in initial capture and recapture probabilities but no examining the range in SVL for individuals. differences between populations (Table 1). Adult We marked 61 C. cerastes (20 adults, 41 juveniles) and population estimates (± standard error) for the 9-ha plots recaptured nine adults and six juveniles during the course were 11.76 ± 1.76 (BMGR) and 17.93 ± 12.58 (BOR) of the study. Ten adult snakes were found at each plot, and juvenile estimates were 70.90 ± 27.48 and 74.47 ±

Table 1. Different models of demographic parameters used to estimate Crotalus cerastes adult (A) and juvenile (B) density at two locationsTable in the 1. DifferentSonoran modelsDesert, of Yuma demographic County, parameters Arizona, 2015. used to Acronyms estimate Crotalus for parameters: cerastes adultsite (s), (A) behaviour and juvenile (b), (B) time (t), and constant (.).density at two locations in the Sonoran Desert, Yuma County, Arizona, 2015. Acronyms for parameters: site (s), behaviour (b), time (t), and constant (.).

(A) Model AICc ∆ AICc AICc Model Number of Deviance Weight Likelihood Parameters s (b) 121.54 0.00 0.60 1.00 3 99.51 s (.) 123.72 2.18 0.20 0.34 2 103.75 (b) 124.74 3.20 0.12 0.20 2 104.77 (.) 125.50 3.97 0.08 0.14 1 107.57 s (t*b) 135.48 13.94 < 0.01 < 0.01 16 84.75 (t*b) 137.49 15.95 < 0.01 < 0.01 11 98.25 (t) 138.95 17.41 < 0.01 < 0.01 10 101.93 s (t) 144.72 23.18 < 0.01 < 0.01 19 86.81

(B) Model AICc ∆ AICc AICc Model Number of Deviance Weight Likelihood Parameters (.) 81.79 0.00 0.46 1.00 3 57.56 (b) 83.34 1.55 0.21 0.46 4 57.07 s (.) 83.83 2.04 0.17 0.36 4 57.55 (t*b) 84.42 2.63 0.12 0.27 11 43.58 s (b) 87.45 5.66 0.03 0.06 6 57.07 s (t*b) 91.20 9.41 < 0.01 < 0.01 21 28.65 (t) 92.56 10.77 < 0.01 < 0.01 12 49.60 s (t) 95.47 13.67 < 0.01 < 0.01 20 35.13

Population aspects of Sidewinders in the Sonoran Desert of Arizona 455

28.69 for the two plots, respectively, probably due to the References higher number of recaptures at BOR. Density estimates Brown, T.W. (1970): Autecology of the sidewinder (Crotalus for adults were 1.31/ha (BMGR) and 1.99/ha (BOR) and cerastes) at Kelso Dunes, Mojave Desert, California. Unpublished juvenile densities were estimated at 7.88/ha and 8.27/ha PhD Thesis, University of California, Los Angeles, USA. for BMGR and BOR, respectively. These data suggest Brown, T.W., Lillywhite, H.B. (1992): Autecology of the Mojave adult to juvenile ratios of 1:6 and 1:4 in the two plots, Desert Sidewinder, Crotalus at Kelso Dunes, respectively. Detection probabilities decreased between Mojave Desert, CA. In: Biology of the Pitvipers, p. 279–308. Campbell, J.A., Brodie, E.D., Eds., Tyler, , USA, Selva. initial capture (BMGR: 0.21 ± 0.9; BOR: 0.09 ± 0.09) Burnham, K.P., Anderson, D.R. (2003). Model selection and and recapture (BMGR: 0.01 ± 0.01; BOR: 0.05 ± 0.03) multimodel inference: a practical information-theoretic for adult snakes, whereas juvenile capture probability approach. Springer Science and Business Media. was constant (0.03 ± 0.01). Campbell, J.A., Lamar, W.W. (2004): The Venomous of Density estimates found in our plots in the Sonoran the Western Hemisphere. Volume II. Ithaca, New York, USA, Desert were much higher than those estimated from the Cornell University Press. Kelso Dunes in the Mojave Desert (Brown, 1970) and Greene, H.W. (1997): Snakes: the Evolution of Mystery in Nature. Berkeley, California, USA, University of California Press. those suggested by Greene (1997). Further, in contrast Hallowell, E. (1854). Descriptions of new reptiles from California. to what Hallowell (1854) remarked, the species is not Proceedings of the Academy of Natural Sciences of Philadelphia “much less abundant” in the Sonoran Desert. The data 7: 91–97. that we provide here suggest that C. cerastes is a very Jones, T.R., Babb, R.D., Hensley, F., Li Wan Po, C., Sullivan, abundant predator in the Sonoran Desert. Road surveys B.K. (2011): Sonoran Desert snake communities at two sites: on the Maricopa Road and Sun Valley Parkway near concordance and effect of increased road traffic. Herpetological Phoenix, Arizona, found C. cerastes to be the most Conservation and Biology 6: 61–71. Leavitt, D.J., Collins, J., Crawford, C., Crayon, J., Grant, T.J., commonly encountered species in the snake community Heatwole, N.B., et al. (2015): Multiyear monitoring (2007– (Jones et al., 2011). In the Sonoran Desert near Organ 2013) of flat-tailed horned lizards (Phrynosoma mcallii). Pipe National Park, Rosen and Lowe (1994) found Herpetological Conservation and Biology 10: 189–202. that C. cerastes ranked as their ninth-most abundant Otis, D.L., Burnham, K.P., White, G.C., Anderson, D.R. (1978): snake species which they attributed to habitat quality. Statistical inference from capture data on closed In addition, during a four-year road survey at Florence, populations. Wildlife Monographs 62: 3–135. Reiserer, R.S. (2001): Evolution of life histories in . Arizona, C. cerastes was the fourth-most commonly Unpublished PhD Thesis, University of California, Berkeley, observed species in the snake community (Sullivan et California, USA. 285 pp. al., 2017). Rorabaugh, J. (2002): Diurnal activity and a minimum population Clear differences exist in the methods used to evaluate density estimate of the shovel-nosed snake snake densities. For example, estimates from Brown (Chionactis occipitalis annulata). Sonoran Herpetologist 15: (1970) were based on tracks and not a mark-and- 32–33. recapture design. However, this does not suggest that Rosen, P.C., Lowe, C.H. (1994): Highway mortality of snakes in the Sonoran Desert of southern Arizona. Biological Conservation the true population density of sidewinders in the area 68: 143–148. investigated by Brown (1970) was higher or lower. Secor, S.M., Jayne, B.C., Bennett, A.F. (1992): Locomotor The habitat available in our study area is part of a very performance and energetic cost of by the snake large contiguous tract of relatively undisturbed land. Crotalus cerastes. Journal of Experimental Biology 163: 1–14. As such, we echo the sentiment of Rosen and Lowe Sullivan, B.K., Leavitt, D.J., Sullivan, K.O. (2017): Snake (1994) regarding habitat quality. Other species communities on the urban fringe in the Sonoran desert: influences were also found to occur in high densities in this region on species richness and abundance. Urban Ecosystems 20: 199– 206. (Rorabaugh, 2002; Leavitt et al., 2015). However, Webber, M.M., Jezekova, T., Rodrigues-Robles, J.A. (2016): further research is needed to assess the factors that Feeding ecology of sidewinder rattlesnakes, Crotalus cerastes determine good habitat quality for C. cerastes. (). Herpetologica 72: 324–330. White, G.C., Burnham, K.P. (1999): Program MARK: survival Acknowledgements. We thank our field crew, including D. estimation from populations of marked . Study 46: Abbate, R. Rhoads, J. Gonzalez, E. Moreno, W. Crumbo, L. 120–139. Piest, K. Sullivan, A. Commerfield, N. Heatwole, and E. Zamora. Activities on the Barry M. Goldwater Range were supported by A. Rosenberg and R. English. We received helpful comments on Accepted by Maximilian Dehling this manuscript from A.T. Holycross and B.K. Sullivan.