Daniel D. Beck

Ecology and Energetics of Three Sympatric Rattlesnake Species in the Sonoran Desert

I investigated habitat use, home ranges, activity patterns, thermal biology, and energetics of sympatric western diamondback (Crotalus atrox), black-tailed (C. molossus), and tiger rattlesnakes (C tigris) in the Sonoran desert of southeastern Arizona. The three species differed significantly in their choice of habitats, and habitats used by snakes were significantly influenced by season. Crotalus atrox used mainly creosotebush flats, but switched to rocky slopes during winter. Crotalus molossus frequented rocky areas, but during late summer and fall used arroyos and creosotebush flats. Crotalus tigris was a strict rock dweller during winter and spring, but used edges of arroyos during summer. Crotalus atrox, C. molossus, and C. tigris had mean home range sizes of 5.42 ha, 3.49 ha, and 3.48 ha, respectively. Over the

HABITAT USE BY GILA MONSTERS: THE IMPORTANCE OF SHELTERS

Abstract Many desert organisms cope with extreme and variable conditions by retreating to sub-surface refugia, yet little is known of the patterns of refuge use by most desert inhabitants. We investigated shelter use by the Gila Monster, Heloderma suspectum, an ectotherm closely tied to sub-surface refugia in a strongly seasonal desert environment. We addressed hypotheses that ectotherms may use habitats based on availability of shelters, select shelters based on particular cues, respond to seasonal variation in refuge characteristics, and show fidelity to specific retreats. Using radiotelemetry, we monitored microhabitat use by eight to ten Gila Monsters for six years, recording timing, frequency, and duration of visitation to over 250 specific shelters. We used transects to assess shelter availability, recorded structural features of all shelters, and used dataloggers to monitor seasonal changes in microenvironments within subsets of shelters for periods up to two years. Shelters, and the habitats where they occurred, were not chosen by Gila Monsters at random. Heloderma spent more time in areas where a higher density of potential shelters was available, and selected shelters based on rockiness, slope and entrance aspect, depth, humidity, and temperature. Gila Monsters showed longer residence times and greater fidelity to shelters used during extreme periods (e.g., winter) and these patterns were paralleled by seasonal changes in the characteristics of shelters chosen. Winter shelters tended to be south-facing, rockier, deeper, and warmer than those used in other seasons, whereas dry-summer shelters were more soil-like in composition, cooler, and more humid. Gila Monsters showed strong fidelity to specific shelters, some of which were used by two or more lizards, sometimes concurrently. Seasonal variation in use of “social” shelters coincided with annual cycles of intraspecific behaviors and reproduction. Our results underscore the importance of sub-surface refugia in the ecology of a sedentary desert ectotherm. Because many other ectotherms also spend significant periods sequestered in below-ground retreats, it is surprising that ecologists have not more extensively investigated this phenomenon. An understanding of the cues used by desert ectotherms to choose refuge-sites, the spatial and temporal variability in refuge characteristics, and the fidelity shown to particular retreats, may help better explain patterns of habitat selection, behavior, distribution, and abundance.

Ecology and behavior of the Gila monster in southwestern Utah

Activity patterns, behavior, food habits, and thermal biology were investigated by radio- telemetry in a population of banded Gila monsters in southwestern Utah. Twenty-seven Gila monsters were observed within a 2 km2 area. They fed on eggs and young mammals taken from nests. Quantities as large as 210 g, eaten in a single meal, did not appear to be envenomated. Activity peaked between late April and mid June, from 0800 to 1200 h. Distances traveled during activity bouts averaged 210 m (ap- proximately 50 min), although individuals occasionally traveled over 1 km. Lizards were active on less than 10 days/month during their 90-day activity season, spending over 95% of their time below ground in shelters. This low energetic investment to activity is contrary to traditional descriptions of activity of lizards that forage on patchy prey. Gila monsters had a relatively low activity temperature (x = 29.4 C) and at rest spent over 83% of the year at body temperatures of 25 C or below. Lizards occasionally basked near shelters in the spring. Several shelters were reused, some by more than one lizard, occasionally concurrently. Intraspecific interactions, including male combat, observed near shelters suggest that these helodermatids have a structured social system. Analysis of a 3-h fight between two large males revealed similarities with varanid lizard and crotaline snake combat, as well as similarities to combat in captive helodermatids.

Conservation phylogenetics of helodermatid lizards using multiple molecular markers and a supertree approach

We analyzed both mitochondrial (mt-) and nuclear (n) DNAs in a conservation phylogenetic framework to examine deep and shallow histories of the Beaded Lizard (Heloderma horridum) and Gila Monster (H. suspectum) throughout their geographic ranges in North and Central America. Both mtDNA and intron markers clearly partitioned each species. One intron and mtDNA further subdivided H. horridum into its four recognized subspecies (H. n. alvarezi, charlesbogerti,exasperatum, and horridum). However, the two subspecies of H. suspectum (H. s. suspectum and H. s. cinctum) were undefined. A supertree approach sustained these relationships. Overall, the Helodermatidae is reaffirmed as an ancient and conserved group. Its most recent common ancestor (MRCA) was Lower Eocene [35.4 million years ago (mya)], with a approximately 25 my period of stasis before the MRCA of H. horridum diversified in Lower Miocene. Another approximately 5 my passed before H. h. exasperatum and H. h. horridum diverged, followed by approximately 1.5 my before H. h. alvarezi and H. h. charlesbogerti separated. Heloderma suspectum reflects an even longer period of stasis (approximately 30 my) before diversifying from its MRCA. Both H. suspectum (México) and H. h. alvarezi also revealed evidence of historic range expansion following a recent bottleneck. Our conservation phylogenetic approach emphasizes the origin and diversification of this group, yields information on the manner by which past environmental variance may have impacted its populations and, in turn, allows us to disentangle historic from contemporary impacts that might threaten its long-term persistence. The value of helodermatid conservation resides in natural services and medicinal products, particularly venom constituents, and these are only now being realized.

Dry season habitat use by lizards in a tropical deciduous forest of Western Mexico

Tropical deciduous or dry forests are characterized by strong seasonality in precipitation, typically having a prolonged dry season lasting at least four months (Bullock, 1986; Murphy and Lugo, 1986). As the dry season progresses, the forest canopy changes from a relatively homogeneous dense cover of the wet season to a more variable and open canopy (Lott et al., 1987; Bullock and Solis-Magallanes, 1990). As deciduous trees lose their leaves, more sunlight penetrates the canopy and creates a variety of forest gaps and thermal microenvironments on or near the ground. In contrast, forest habitat near seasonally dry watercourses (arroyos), remains green throughout the dry season, providing shaded habitats with dense canopy cover (Lott et al., 1987; Bullock and Solis-Magallanes, 1990). The dry season in a tropical deciduous forest represents a challenging time of year for most ground dwelling vertebrates. Water and energy resources are at the yearly low (Janzen and Schoener, 1968; Lister and Garcia, 1992), and thermal options may also be reduced, especially in the more shaded habitats of arroyos. Many vertebrates show reduced activity or seasonal changes in habitat use during the dry season (Beck and Lowe, 1991; Ceballos, 1995). Other species may move away from upland habitats and into arroyos or watercourses, which are used as dry season refuges (Ceballos, 1990). Those that remain active tend to be juveniles or adults of smaller species (Fleming and Hooker, 1975; Lister and Garcia, 1992; Casas-Andreu and Gurrola-Hidalgo, 1993; Fitzgerald et al., 1999). We know little about how dry forest lizards respond to seasonal changes in habitat structure or of the patterns of activity exhibited by lizards that remain active during the dry season. Our study examines how lizard habitat use and activity (i.e., species found to be active, timing, and amount of activity) are influenced by the variability in forest structure during the dry season in a tropical deciduous forest in southwest Mexico. We address the following questions: (1) During the dry season, does lizard activity differ between arroyo and upland habitats? (2) Is lizard activity related to forest canopy cover during the dry season?

Ecology and Ontogenetic Variation of Diet in the Pigmy Short-Horned Lizard (Phrynosoma Douglasii)

ABSTRACT To date, the diet of the pigmy short-horned lizard (Phrynosoma douglasii) is not known. We report the diet of the pigmy short-horned lizard to determine whether it shows a more generalized diet, similar to other short-horned lizards or a more specialized diet consisting primarily of ants. We compare variation in diet among habitat variables and age/sex classes. We also compare ant head capsules consumed among age/sex classes to determine if lizard groups consume ants of varying size and diversity proportional to their body sizes. Similar to other short-horned lizards, P. douglasii consumes relatively lower proportions of ants (71%) than highly myrmecophagous horned lizard species, followed by pebbles (13%) and Coleopteran insects (11%). Aside from terrain, diet varies among all habitat variables measured, but especially among age and sex classes; neonates feed almost exclusively on ants (89%) while adults consume fewer ants (72%) and yearlings consume the lowest proportion of ants (60%). Most ants consumed by adults represent a single ant genus (Camponotus), while yearlings and neonates consume multiple ant genera of smaller sizes (Camponotus, Pheidole, Tetramorium). We found a significant positive correlation between lizard SVL and the size of ant heads in the diet of P. douglasii. These results are important in understanding variation in diet and ecology of the pigmy short-horned lizard and also in addressing foraging and diet in other insectivorous Phrynosomatid lizards, particularly horned lizards.

ECOLOGY OF THE PYGMY SHORT-HORNED LIZARD (PHRYNOSOMA (TAPAJA) DOUGLASII) IN WASHINGTON

Abstract We investigated population characteristics, microhabitat use, and activity patterns of Phrynosoma (Tapaja) douglasii (Pygmy Short-horned Lizard) within shrub-steppe habitat in Washington. Females were significantly larger (and more commonly encountered) than were males. Overall, lizards preferred lithosol microhabitat, which is characterized by rocky soils and sparse vegetation. Age, sex, and season, however, affected how lizards used lithosol, loamy, and ecotone microhabitats. Lizard age also affected daily, monthly, and seasonal activity. Adult activity peaked in June, yearling activity in April, and neonate activity in July. During spring and fall, adult activity peaked when daytime temperatures were highest, whereas in summer, the activity peak occurred in early morning and evening. In contrast, neonates remained active during temperature maximums in summer and throughout the day in fall. Although lizards preferred relatively open terrain, they were found closer to shrubs than expected, based on comparisons with random sites. Our results underscore the importance of seasonal variation and age in habitat use and activity patterns of P. (Tapaja) douglasii.

Habitat Use and Activity Patterns of a Terrestrial Turtle (Rhinoclemmys rubida perixantha) in a Seasonally Dry Tropical Forest

Abstract We report the results of a field study on Mexican Spotted Wood Turtles (Rhinoclemmys rubida perixantha) in a seasonally dry tropical forest of coastal Jalisco, Mexico. We used field surveys, trail spools, and radio telemetry to investigate activity patterns, estimate home range size with three different techniques, and develop a generalized linear model to identify features associated with habitats used by R. r. perixantha. We found that turtles were most frequently active at midday, with peak activity occurring from 0900 to 1500 h. During the dry season (January–mid-June), R. r. perixantha showed reduced activity (fewer movements and shorter travel distances) compared to the wet season (late June–September). Home range size did not differ among the three methods we compared, and all estimates revealed that R. r. perixantha have small home ranges, with males having larger home ranges than females. Sites used by turtles were positively associated with leaf litter and woody debris, herbaceous plants, vegetation, vine-like shrubs, and sloped terrain, and negatively associated with bare ground. Our findings can be used to strengthen future conservation efforts for R. r. perixantha, as well as other terrestrial geoemydids.

Use of Communal Shedding Sites by the Northern Pacific Rattlesnake (Crotalus oreganus oreganus) in Central Washington State

Ecdysis (shedding of skin) is an important event for a snake. For rattlesnakes, most adults shed only once per year, although some adult males may shed more than once per year (Klauber 1972; Diller and Wallace 1984, 2002; Macartney and others 1990). During this time, feeding and mating opportunities are compromised, snakes are more vulnerable to predators, and they show a narrowed range of tolerance to temperature and humidity (Klauber 1972; Peterson and others 1993). Females may be particularly receptive to mating immediately after shedding, as sex hormones may be released from the skin (Graves and Duvall 1987; Aldridge and Brown 1995) and males may respond to the female shedding cycle by searching for mates (Schuett 1992). Given these ecological, behavioral, and physiological consequences, the decision of where to shed becomes particularly important for a rattlesnake. Like many northern latitude squamate reptiles, rattlesnakes gather (sometimes in large numbers) and overwinter communally in subsurface rock shelters (hibernacula) to escape potentially lethal winter temperatures (St. John 2002). Northern Pacific Rattlesnakes (Crotalus oreganus oreganus) are able to locate hibernacula by recognizing structural qualities that afford thermal protection (Gienger and Beck 2011). Such qualities allow for use by several different age and size classes of C. o. oreganus (Gregory 1984). In the spring, adult males may be the first to emerge before perhaps making long-distance movements to foraging and breeding areas (Graves and Duvall 1990). Adult females with developing follicles openly bask, and at this time copulations may take place (Fitch 1970). Young snakes bask side-by-side with each other and adults before leaving to forage. Similarly, during fall ingress, hibernacula afford all individuals protected basking opportunities to fully digest their last meals (Greene 1997). Here we describe both direct and indirect observations of multiple shedding aggregations near a communal hibernaculum of Crotalus o. oreganus from a location in central Washington State. We present evidence that, in addition to overwintering hibernacula, shed rocks may comprise an important feature of the social structure of this population of rattlesnakes. Our study site is in Grant County, approximately 8 km south of George, Washington (elevation: 370 m), and located in the shrubsteppe of the Columbia Basin eco-region. This is a habitat characterized by open, sandy flats with Big Sagebrush (Artemesia tridentata), Stiff Sagebrush (A. rigida), buckwheat (Erigonium spp.), rabbitbrush (Chrysothamnus spp.), and Bluebunch Wheatgrass (Pseudoroegneria spicata), with small to large basalt rock outcrops scattered throughout the landscape. At the southeastern edge of the site is a large, wetland dominated by Russian Olive (Elaeagnus angustifolia), willow (Salix spp.), cattail (Typha spp.), and a mix of non-native invasive species. We haphazardly searched for snakes and potential shed rocks on an irregular schedule throughout the active season (late March through early October) in 2012 and 2013. In August and September 2012, we observed multiple C. o. oreganus skins at 3 separate basalt outcrops (Table 1). The 1st outcrop was found on 14 August 2012, and was approximately 0.7 km east from the only 2 overwintering dens in this area (Shed Rock 1; Fig. 1A). This outcrop had 5 adult-sized skins along the edges of the rocks or below the largest rock (approximately 1.0 x 0.6 x 0.3 m) in that outcrop. Less than 1 m away from the large rock, 2 adult C. o. oreganus (1 male, 1 female) were observed coiled together under a smaller rock. This outcrop was ,3 m away from the edge of the wetland area, receiving partial shade from overhanging willow and Russian Olive. At a second, smaller GENERAL NOTES