Spatial Ecology of the Trans-Pecos Rat Snake (Bogertophis Subocularis)

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2012-01-01 Spatial Ecology Of The rT ans-Pecos Rat Snake (bogertophis Subocularis) In The hiC huahuan Desert Of Trans-Pecos Texas Arturo Rocha University of Texas at El Paso, [email protected]

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Recommended Citation Rocha, Arturo, "Spatial Ecology Of The rT ans-Pecos Rat Snake (bogertophis Subocularis) In The hiC huahuan Desert Of Trans-Pecos Texas" (2012). Open Access Theses & Dissertations. 2175. https://digitalcommons.utep.edu/open_etd/2175

This is brought to you for free and open access by DigitalCommons@UTEP. It has been accepted for inclusion in Open Access Theses & Dissertations by an authorized administrator of DigitalCommons@UTEP. For more information, please contact [email protected]. SPATIAL ECOLOGY OF THE TRANS-PECOS RAT SNAKE (BOGERTOPHIS

SUBOCULARIS) IN THE CHIHUAHUAN DESERT OF TRANS-PECOS TEXAS

ARTURO ROCHA

Department of Biological Sciences

APPROVED:

______Jerry D. Johnson, Ph.D., Chair

______Carl S. Lieb, Ph.D.

______John C. Walton, Ph.D.

______Benjamin C. Flores, Ph.D. Interim Dean of the Graduate School

i SPATIAL ECOLOGY OF THE TRANS-PECOS RAT SNAKE (BOGERTOPHIS

SUBOCULARIS) IN THE CHIHUAHUAN DESERT OF TRANS-PECOS TEXAS

ARTURO ROCHA, B.S.

THESIS

Presented to the faculty of the Graduate School of

The University of Texas at El Paso

in Partial Fulfillment

of the Requirements

for the Degree of

MASTER OF SCIENCE

Department of Biological Sciences

THE UNIVERSITY OF TEXAS AT EL PASO

August 2012

ii ACKNOWLEDGEMENTS

Funding by the National Science Foundation (FSML) for the facilities at Indio Mountains

Research Station (IMRS) provided the main core of funding through grants, making this study possible.

Professors and committee members Carl S. Lieb, and John C. Walton provided valuable input for this study, as well as relevant literature for this project.

I wish to thank Dominic I. Lannutti, a Professor at El Paso Community College (EPCC) and

Dr. William P. Mackay at UTEP, who first introduced me to field ecological studies.

My advisor, Dr. Jerry D. Johnson (“Dr. J”) provided all the necessary resources both in the field, as well as in the input in the study and the final versions of this thesis. Dr. Johnson is also responsible for the maintaining the IMRS facilities, overseeing the research station and providing the direction to ongoing research activities. His dedication to IMRS has led to numerous publications and collaborations with other researchers who utilized the research station. Dr.

Johnson also cooked meals at IMRS, allowing myself and other graduate students to continue with their research with minimal distractions, as wells as preparing and assistance for the required protocols, proposal, and presentations to numerous events relating to this study. For all this, I am grateful.

When I first took the Field Biology course with Dr. Johnson, I met Dr. Vicente Mata-Silva.

During that course, I volunteered to help radiotrack Crotalus lepidus on IMRS that was part of his dissertation study at the time. It was in these initial steps that led me to achieve my B. S. in

iii Biological Sciences, and subsequently working on my graduate studies. Dr. Mata-Silva provided valuable advice, as well as words of encouragement throughout the duration of this study. I witnessed his gradual journey from Ph. D. student, to candidate, to full realization of the title

“Doctor”, although he always put in the time to assist myself (and others) in our research. I thank you as a colleague, and as a friend for all your help.

There are individuals I wish to thank that I met throughout the duration of my research out at

IMRS. Prior to my graduate studies and the initial phases of this study, these individuals befriended me to make the transition of a new environment flow more easily. As colleagues, they also shared a similar interest in herpetology and science in general, and numerous entertaining stories we’ve shared at IMRS. Steve “Chalupa” Dilks, whom taught us the “two rock method” while out in the field. Those out in the field will be the only ones who understand what that means. Luis “El Napoleón” Miranda, showed me around IMRS on my first visits. Also there is a tale of his at IMRS that is humorous, that only a few will know about, but it involves a mine and apparel. Anthony “Crazy Tony” Gandara and I initially assisted Vicente in the beginning phases of his study. How a person hiking through rugged terrain, while explaining the relationship between memes and genes, fall into a thicket of Agaves, get up, and continue with the conversation as if nothing happened is beyond words. Hector “Bionic Leg” Riveroll Jr. served as an unofficial “tutor”, or “guru” to many students, also joined us in radiotracking snakes on several occasions. In the latter phases of this study, individuals such as William “Hey Art, check this out” D. Lukefahr (whose rants are entertaining as well as engaging), Julia “Butterfingers”

Alva, Ross “Hey y’all!”Couvillon, and Geoffrey “Now hold on!”Wiseman also provided companionship while at IMRS.

iv All these individuals and myself helped one another out at IMRS, be it from preparing food, changing tires, driving in flash floods, fixing the roads (to this day I still don’t know which rocks

Dr. J was referring to) after the rains, and in times of extremes (hot and cold), looked out for one another. Thank you guys!

I am thankful to Dr. Rebecca Escamilla (who graduated in the spring of 2012) whom assisted me in GIS maps and related applications. She kindly allowed me to use her GIS map of IMRS for use in the analysis of field data.

To my parents, Norma Rocha and Alejandro Rocha, who always supported my studies and provided a pillar of support. I could not have accomplished this project without them. My brothers Alex, Abraham, and sister Raquel were also supportive in all aspects. Abraham accompanied me once at IMRS during the study. Although it possibly raised more questions than answers, his presence there provided a bridge to my family in exactly what was I doing “out there”. In all, to my family, thank you for your love and encouragement.

This study would have been far more difficult without the use of the ATVs out at IMRS, which would have meant hiking even longer distances than those experienced during the study. I thank Department of Biology professors Dr. Craig. E. Tweedie as well as Dr. Johnson for the vehicles.

I thank all the students from the UTEP Field Biology and Maymester courses whom assisted me and were also fascinated with the nature of my project.

To all herpetologists, especially those who’ve radiotracked snakes, their efforts have motivated me throughout the study.

v Finally, I want to thank the UTEP Department of Biological Sciences and the Graduate

School in which supported trips to national and international meetings. This allowed me to give oral and poster presentations on the spatial ecology of the Trans-Pecos Rat Snake.

vi ABSTRACT

The Trans-Pecos Rat Snake (Bogertophis subocularis) is a medium to large rat snake that occurs from south-central New Mexico, south-central Texas, down into the north-central and northeastern states of Mexico. There is paucity in the ecology of B. subocularis to date. Some

North American colubrid snakes, such as Thamnophis sirtalis, are the most represented species in thermal ecology and life history studies in all reptiles. There is nothing known on the winter ecological aspects of this species, and very little information regarding its overall ecology. The goal of this study is to determine home range, movement patterns, habitats and utilization of microhabitats, and the overwintering characteristics of the Trans-Pecos Rat Snake (Bogertophis subocularis) in the Chihuahuan Desert on the Indio Mountains Research Station (IMRS) located in Hudspeth County, in far west Texas. From the summers of 2009 – 2011, six adult snakes were captured, monitored, and radiotracked in their active seasons (May – October) and winter seasons (November – March) (two males and three females). Average home ranges occupied by individuals was large (58.8 ha), and ranged from 20.9 to 123.6 ha. Snakes emerged from their overwintering sites in late April to early May, and returned to those sites in late October to early

November. By sex, mean home ranges were 46.5 ha (n = 3) for females and 77.2 ha (n = 2) for males. Snakes occupied a small core areas (50 % kernel) (average 0.000005 ha), in which on average, males occupied slightly large core areas (0.000006 ha) than females (0.000004 ha).

Daily movement for all snakes averaged 17.3 m/d, with females moving at a greater rate (18.4 m/d) than males (14 m/d). There was no significance between daily movement rates by month,

vii however, daily movement rates between sexes was statistically significant. The greatest mean distance by month snakes traveled was May, followed by July, June August, September and

October.

Bogertophis subocularis was observed in four habitats on IMRS, and snakes were mostly associated rocky slope habitats (n = 74, 43 %), followed by alluvial flats (n= 43, 25 %), alluvial slopes (n= 32, 18%), and arroyo habitats (n = 24, 14 %). Snakes were found in five identified microhabitats, found under shrubs (36 %), followed by under rocks (20 %), and in burrows (20

%), with lesser occurrences under plant litter (14 %), and in crevices (10 %). The composition of microhabitats showed that snakes selected microhabitats in which vegetation was the most represented (41 %), followed by rocks (30 %), plant litter (20 %), and gravel (9 %). Bogertophis subocularis preferred microhabitats with specific compositional characteristics (vegetation) from a comparison of selected sites (n = 172) and random sites (n = 172).

The mean body temperature of B. subocularis during the active season was 28.7° C, of which males (29° C) were generally higher than females (28.6° C). The months of July (31.8°

C) and May (25.8° C) were the warmest and coolest (respectively) throughout the active seasons.

The mean number of days that snakes resided in their overwintering sites during the winter periods was 172.5 days. Snakes had a mean, cold body temperature of 15.3° C throughout the winter periods, of which November (23.2° C) and January (12.2° C) were the warmest and coldest months, respectively. The range of body temperatures during the winter periods were from 2.3° C to 26.5° C. Snakes overwintered singly at different sites from late October or early

November to late April/early May. All snakes overwintered at high slopes than normally found during surface activity throughout the active seasons.

viii TABLE OF CONTENTS

ACKNOWLEDGEMENTS……………………………………………………………………………iii

ABSTRACT………………………………………………………………………………………..vii

TABLE OF CONTENTS……………………………………………………………………………..Ix

LIST OF TABLES……………………………………………………………………………………x

LIST OF FIGURES…………………………………………………………………………………xii

INTRODUCTION……………………………………………………………………………………1

METHODS AND MATERIALS……………………………………………………………………….9

RESULTS………………………………………………………………………………………….21

DISCUSSION………………………………………………………………………………………46

LITERATURE CITED…………………………………………………………………………….....70

APPENDIX 1………………………………………………………………………………………89

VITA………………………………………………………………………………………………95

ix LIST OF TABLES

Table 1. Home range (MCP) and movement patterns of six B. subocularis in IMRS.

(Crosses denote the death of individual 06 early in the study) (Total m and mean

daily movement rate reflects data for the snakes’ active season)………………..23

Table 2. Frequency and percentage of microhabitats utilized by B. subocularis at IMRS..28

Table 3. Frequency and percentages of vegetation classes observed for snakes at IMRS (n

= 173 observations)………………………………………………………………31

Table 4. Overwintering characteristics of five B. subocularis on IMRS during the winters

of 2009-2010 and 2010-2011. * denotes the lost individual during the ingress date

range. …………………………………………………………………………...36

Table 5. Body temperatures of five individual B. subocularis during the winter periods of

2009-2010 and 2010-2011……………………………………………………….37

x LIST OF FIGURES

Fig. 1. An adult male Bogertophis subocularis (1,100 mm SVL) from Indio Mountains

Research Station, Hudspeth County, Texas……………………………………….5

Fig. 2. Geographic distribution and localities of Bogertophis subocularis. Solid dots refer

to known localities of B.s. subocularis (encircled star = type locality), and solid

squares refer to B. s. amplitonus (solid star = type locality). Half-filled squares are

possible integrades. White stars indicate fossil records (from Schulz, 1996)…….6

Fig. 3. Google Earth map depicting the boundaries of Indio Mountains Research Station

(white). The bottom boundary represents the United States-Mexico international

boundary (yellow). The thumbnail represents the approximate location of IMRS

headquarters compound…………………………………………………………10

Fig. 4. IMRS headquarters compound looking west…………………………………….11

Fig. 5. Typical mountainous landscape within IMRS…………………………………...11

xi Fig. 6. Passive Integrative Transponder (PIT-tag; Avid Inc.) used to identify snakes (2.1

mm in diameter, 15.0 mm in length)……………………………………………14

Fig. 7. SB-2 Transmitter (5 g) implanted into body cavity of B. subocularis (Holohil

Systems Ltd.)…………………………………………………………………….15

Fig. 8. X-ray depicting the typical location of the implantation of a temperature-sensitive

transmitter in a Mojave Rattlesnake (Crotalus scutulatus). Note the antenna

running laterally under the snake’s skin (from

http://www.holohil.com/snake.htm)...... 16

Fig. 9. Mean total distance traveled in meters by five Bogertophis subocularis (n = 173)

by month on IMRS during the active season. Bars denote standard error………24

Fig. 10. Mean daily distance traveled in m by sex of five Bogertophis subocularis (n =

173) by month on IMRS during the active season. Lines with circles are females,

and lines with triangles are males ………………………………………………24

xii Fig. 11. Relationship between body size (total body length; TBL) and annual

minimumconvex polygons (MCP) home range size for 5 adult Trans-Pecos Rat

Snakes (Bogertophis subocularis) at IMRS……………………………………...25

Fig. 12. Photographs of identified generalized habitats used in the study that snakes were

observed. Clockwise from top left: rocky slope, alluvial flat, alluvial slope, and

arroyo……………………………………………………………………………26

Fig. 13. Habitats utilized by B. subocularis at IMRS during the active season (n = 173

observations)……………………………………………………………………27

Fig. 14. Monthly habitats utilized by B. subocularis on IMRS during the active season (n

= 173 observations). Bars indicate: filled = rocky slopes, non-filled = arroyo;

diagonal = alluvial flat; checkered = alluvial slope……………………………...27

Fig. 15. Ground cover composition (%) of microhabitats utilized by B. subocularis (n =

173 observations). Bars denote standard error. Numbers in squares are

percentages………………………………………………………………………29

xiii Fig. 16. Mean percentage of ground cover (by month) of microhabitats utilized by B.

subocularis during the active period. Bars denote standard error. Symbols

represent the structural components of microhabitats (squares = vegetation, filled

circles = gravel, filled triangles = plant litter, and exes = rocks)………………30

Fig. 17 . Box plot of mean Tb of B. subocularis during the active season (n = 173

observations)……………………………………………………………………..33

Fig. 18. Box plot of mean Tb of female B. subocularis during the active season (n = 107

observations)..……………………………………………………………………34

Fig. 19. Box plot of mean Tb of male B. subocularis during the active season (n = 66

observations)……………………………………………………………………..34

Fig. 20. Tb profile of B. subocularis during the active season by month. Bars denote

standard error and numbers in boxes are average

temperatures……………………………………………………………………35

xiv Fig. 21. Mean temperatures of temperature variables (Tb = body temperature, Ta = ambient

temperature, Ts= substrate temperature, and Tmicro = microhabitat temperature) of

snakes by month during the active season……………………...... 35

Fig. 22. Box plot of body temperatures (Tb) during the two winter periods of five

individual B. subocularis at IMRS. Bars denote standard error (n= 2445

observations). ……………………...... 38

Fig. 23. Box plots of body temperatures (Tb) of females and males B. subocularis during

the two winter periods at IMRS. Bars denote standard error. …………………...39

Fig. 24. Mean winter Tb profile by month of B. subocularis at IMRS. Bars denote standard

error (n = 2445 observations). Number in boxes are means…………………..…39

Fig. 25. Mean daily Tb of B. subocularis (by hour) during the two winter periods at IMRS.

Bars denote standard error (n = 2445 observations)……………………………..40

Fig.. 26. Mean daily Tb of B. subocularis (by hour) during the two winter months of

November on IMRS (n = 510 observations)……………………………………..41

xv Fig. 27. Mean daily Tb of B. subocularis (by hour) during the two winter months of

December on IMRS (n = 763 observations)...…………………………………..41

Fig. 28. Mean daily Tb of B. subocularis (by hour) during the two winter month of January

on IMRS (n = 509 observations)…………………………………………………43

Fig. 29. Mean daily Tb of B. subocularis (by hour) during the two winter month of

February on IMRS (n = 267observations)…………………………………….…43

Fig. 30. Mean daily Tb of B. subocularis (by hour) during the two winter month of March

on IMRS (n = 395observations)………………………………………………….44

Fig. 31. Flat Top Mountain, a distinctive mesa and ridge system containing rocky slopes

that harbored overwintering sites for most B. subocularis studied herein. Snakes

move downward to other habitats during the activity season……………………48

Fig. 32. Typical overwintering site of female B. subocularis (ID 03), partially exposed

outside its overwintering site…………………………………………………….48

xvi INTRODUCTION

Today, the loss of habitat due to anthropogenic activities is one of the main causes for biodiversity loss on a worldwide scale (Wilson, 1992). The way an organism uses space in its environment is an integral element of overall fitness, and in the case of vertebrates, habitat loss or degradation has resulted in local to global decreases or extinctions (Porter et al., 2000; Gaston et al., 2003). However, in respect to the herpetofauna, lack of information of population viability is especially acute for snakes, which have been historically less represent in ecological literature than other major vertebrate groups (Shine and Bonnett, 2000; Bonnett et al., 2002). Several factors probably contribute to this disparity, as snakes are often highly cryptic, nocturnal, and many have low population densities (Parker and Plummer, 1987; Greene, 1997).

Knowledge on certain aspects of snake ecology, such as information on spatial ecology (e.g., habitat associations, home range, movement patterns, resource utilization) is crucial for determining essential ecological factors and for implementing conservation practices benefiting concerned species (Dodd, 1993). The study of movement patterns and home range dimensions are fundamental features of snake ecology and they reveal important indicators of resource requirements (Plummer and Congdon, 1994; Johnson, 2000). Ectotherms have many ecological constraints, such as abiotic and biotic factors limiting use of space and access to resources

(Macartney et al.,1988). One of the central themes in ecology is how organisms use spatial resources for organizing, structuring, and defining home ranges and associated territories. The recent development and use of modern technology in herpetology, especially radiotelemetry, has enhanced our understanding of spatial ecology in snakes and disclosed how environmental

1 factors control the natural history of organisms at both the individual and population levels

(Cooke et al., 2004).

Snakes are among the foremost predators in many ecosystems, exerting heavy mortality on prey species (Daly et al., 1990; Weatherhead and Blouin-Demers, 2004; Robinson et al., 2005;

Sperry et al., 2008), while also serving as essential prey for others as well (Janzen, 1976; DuVal et al., 2006; Moreno-Rueda and Pizarro, 2007). Predation pressure by snakes may also influence prey directly by affecting habitat use, foraging, and related activities (Weldon et al., 1987;

Dickman, 1992; Kotler et al., 1993, Bouskila, 1995). Predation risks, specifically from snakes, have been proposed as a driving factor in the evolution of some avian migratory patterns (Boyle,

2008), and even development of the primate brain (Isbell, 2006).

Information concerning movement and home range of most snakes is limited, largely because of their secretive behavior, which in turn leads to the perception that they are difficult to use for ecological research (Reinert, 1992; Bonnet et al., 2002). The difficulty observing free-ranging snakes has been amplified by general confusion due to inadequate or biased information on snake movement patterns and by erroneous descriptions of habitat preference (Reinert, 1984;

Gregory et al., 1987; Tiebout and Cary, 1987). Most recently, use of radiotelemetry has lead to a more precise way to investigate long-term and high resolution studies of snake behavior in the field (Brown and Parker, 1976; Reinert, 1984; Duvall et al., 1985). With radiotelemetry, investigators have been able to observe snakes selecting different habitats on a yearly basis, as well as monitoring more specific activities such as feeding, mating, overwintering site selection, and behavior related to environmental thermoregulation (Reinert, 1992; Beaupre, 1995). The study presented herein used radiotelemetry technology to determine movement patterns, home

2 ranges, and habitat uses by the Trans-Pecos Rat Snake (Bogertophis subocularis) in the

Chihuahuan Desert on Indio Mountains Research Station (IMRS), Hudspeth County, Texas.

Rat snakes in general are a group of related genera belonging to the family Colubridae inhabiting portions of the Eurasian and Nearctic biogeographical regions of the world. In North

America, rat snakes belonging to the genera, Bogertophis, Pantherophis, Pseudelaphe, and

Senticolis (Pyron and Burbrink, 2009; but also see Collins and Taggert, 2008), inhabit a large geographic area from Canada southward through Mexico into Central America. As a whole, New

World rat snakes are part of the Lampropeltini tribe; a group which diverged from the Old World rat snakes and ultimately dispersed across Beringia in the late Oligocene/early Miocene

(Burbrink and Python, 2009; Burbrink and Lawson, 2007).

With the exception of Fox Snakes, Corn Snakes, and Woodland Rat Snakes (genus

Pantherophis), few ecological investigations have been initiated, especially in spatial ecology.

Probably the best known species group, in respect to spatial ecological studies, is the Woodland

Rat Snakes, formerly regarded as subspecies of Pantherophis obsoletus (i.e. P. alleghaniensis, P. bairdi, P. obsoletus, and P. spiloides) (Blouin-Demers et al., 2007; Blouin-Demers et al., 2002;

Blouin-Demers and Weatherhead, 2001, 2002; and Durner and Gates, 1993). This monophyletic group has an extensive geographic range in eastern North America from Canada to the Gulf of

Mexico and west to central Texas (Conant and Collins, 1998). Few studies focusing on the ecology of B. subocularis are available, although the species is a prime model for spatial ecology using radiotelemetry because of its large size and relatively common occurrence in mountainous

Chihuahuan Desert scrubland habitats in western Texas, and adjacent areas of New Mexico and

Mexico. It is also interesting that Bogertophis, Pseudelaphe, and maybe Senticolis are more closely related to other colubrid genera (e.g., Arizona, Cemophora, Lampropeltis, Rhinocheilus,

3 and Stilosoma, than they are to Pantherophis, whose sister group is Pituophis (Pyron and

Burbrink, 2009; Rodríguez-Robles and Jesús-Escobar, 1999).

Bogertophis subocularis (Brown, 1901) is a medium to large-sized and normally yellowish species with a series of H-shaped dorsal blotches and anterior dark dorsal stripes (Fig. 1) with a maximum total length of 1,680 mm (Rhoads, 2008). A key phenotypical characteristic of B. subocularis are its large, protruding eyes (Schulz, 1996). Bogertophis subocularis possess a unique, high number of chromosomes (2n = 40), which along with its sister species, Bogertophis rosaliae (2n = 38) are distinct from other New World rat snakes (Dowling and Price, 1988).

Bogertophis subocularis and B. rosaliae also possess other distinguishing morphological characters, including loriolabial scales, and a higher frequency of supralabial and temporal scales, and dorsal scale rows (Keogh, 1996).

Bogertophis subocularis ranges from the vicinity of Elephant Butte Reservoir in south-central

New Mexico to the south-central Rio Grande of Texas (Malone, 2001), southward into the

Mexican states of Coahuila, Chihuahua, Nuevo León and Durango (Sawyer, 1993; Sawyer and

Baccus, 1996; Webb, 1990; Degenhardt and Degenhardt, 1965; Degenhardt et al., 1996; Rhoads,

2008; Worthington, 1980; Morafka, 1977; Tanner, 1985; Fig. 2). It is normally associated with the arid habitats of the Chihuahuan Desert and generally favors dry, rocky terrain, although it sometimes reaches into desert grassland and even higher into juniper/ponderosa pine habitats

(Rhoads, 2008; Degenhardt et al., 1996). The species, along with the other native herpetofauna of the Chihuahuan Desert occur in one of the most biodiverse areas of all desert ecoregions

(Fitzgerald et al., 2004).

4 Bogertophis subocularis is currently recognized as containing two pattern classes (as desbribed by Grismer, 2002), previously regarded as subspecies, B. s. subocularis and B. s. amplitonus, based upon variable clinal morphological patterns including features of dorsal body blotch features. The B. subocularis Amplitonus pattern class is limited to the Mexican state of

Durango, and suppossedly integrades with the B. subocularis Subocularis pattern class in the

Mexican states of Coahuila and Nuevo Leon (Webb, 1990) (Fig. 2). The mention of intergradation insinuates a geographical cline between the two pattern classes that reflects continuous gene flow. However, the subspecies category in modern taxonomy is of questionable legitimacy (Johnson et al., 2010), so it will not be recognized herein. This decision is due to the acceptance of the general lineage concept of species (de Queiroz 2005), which by inference does not identify continous clinal intergrading subpopulations as belonging to a formal taxonomic category; thus, it rejects a formal subspecies category.

FIG 1. An adult male Bogertophis subocularis (1,100 mm SVL) from Indio Mountains Research

Station, Hudspeth County, Texas.

FIG. 2. Geographic distribution and localities of Bogertophis subocularis. Solid dots refer to known localities of B.s. subocularis (encircled star = type locality), and solid squares refer to B. s. amplitonus (solid star = type locality). Half-filled squares are possible integrades. White stars indicate fossil records (from Schulz, 1996).

6 The ecophysical constraints of ectotherms have profound limitations on their behavior and physiology (Huey, 1982; Angilletta Jr. et al., 2002). Thus, these physiological proceses are all strongly temperatue dependent (Keogh and DeSerto, 1994). As ectotherms, snakes, and ultimately their ecology is influenced by regulation of body temperatures, which makes it one of the most important aspects affecting their fitness (Huey and Kingsolver 1989). In ectotherms, thermoregulation is a complex behavioral and physiological process. In reptiles, although being model organisms in thermal biology, physiological process that drive thermoregulation remain uncertain (Seebacher and Franklin, 2005). The link between thermoregulation and habitat selection is also crucial, as microhabitats can serve as refuges aiding achievement of optimal body temperature and ultimately, timing of behavioral activity (Huey et al., 1989, Grant 1990).

With this relationship, the cold, winter months in temperate latitudes often serve as reptiles’ primary period of inactivity. In New World rat snakes, latitude variation in seasonal flux can regulate their winter behavioral disposition (Sperry et al., 2010). Latitudinal variation exhibited in the southern populations of P. obsoletus reflects lack of hibernation leading to winter diurnal activity, whereas in warm summer months they become nocturnal (Sperry et al., 2010).

However, B. subocularis is reported to be always nocturnal and rarely or never becomes surface active during winter. The Chihuahuan Desert climate, although relatively cool to mild overall in the winter, has regular extended periods when temperatures plummet to less than 10° C on average, thus limiting surface activity during the winter months (Schmidt, 1986).

To date, only Sawyer (1993) and Sawyer and Baccus (1996) have reported on the ecology of

B. subocularis in any detail. The information presented herein will help qualify and quantify various ecological aspects of B. subocularis in the Chihuahuan Desert on IMRS. The information

7 can also be used to aid conservation biologists by identifying the ecological structure needed to preserve critical landscape components necessary for continued survival of B. subocularis.

Given the lack of prior field-based ecological information on B. subocularis, the present study addresses the following facets of the species’ ecology on IMRS using radiotelemetry: 1).

Distance and direction traveled, and home range utilized on a yearly and seasonal basis. 2).

General habitats and microhabitats used by the species throughout the year, including the composition of vegetation communities, geologic features, and hibernacula sites. 3). Variation in preferred body temperature throughout the year by males and females, including during winter dormancy, and its effect on movement patterns and habitat utilization. Protocols for this study were approved by the UTEP Institutional Animal Care and Use Committee, #A-201004-2. The style for the text follows the Journal of Herpetology.

8 METHODS AND MATERIALS

Description of Study Area. - This study took place on the 40,000 acre Indio Mountains

Research Station (IMRS) (centered on 30.75°N, 105.00°W; Figs. 3 and 4), which is managed by the University of Texas at El Paso (UTEP). IMRS is situated in the southeastern corner of

Hudspeth County, Texas, approximately 40 km southwest of Van Horn. Johnson (2000) and

Worthington et al. (2004; http://research.utep.edu/indio/) provide additional information on

IMRS, some of which is presented below.

FIG. 3. Google Earth map depicting the boundaries of Indio Mountains Research Station (white).

The bottom boundary represents the United States-Mexico international boundary (yellow). The thumbnail represents the approximate location of IMRS headquarters compound.

FIG. 4. IMRS headquarters compound looking west.

FIG. 5. Typical mountainous Chihuahuan Desert landscape within IMRS.

11 IMRS is delineated by the Indio Mountains (Fig. 5) that generally run north to south, with most main slopes facing east and west. The formation of the Indio Mountains oriented a shift in direction south of the Chihuahua Trough (Carciumaru and Ortega, 2008). Much of the mountainous substrate is composed of intermittent conglomerate, sandstone, limestone, and igneous rocks. Alluvial flats occur in the lower elevations, and most arroyos drain into the Rio

Grande to the southwest and east toward the Green River. The average elevation at IMRS is approximately 1100 m, but some peaks may exceed 1300 m (e.g., Squaw Peak). The vegetation community is typically Chihuahuan Desert scrub, consisting of dominant species such as

Creosotebush (Larrea tridentata), White-thorn Acacia (Acacia constricta), Catclaw (Acacia greggi), and Honey Mesquite (Prosopis glandulosa) that grow mostly on alluvial flats and along arroyos; and Lechuguilla (Agave lechuguilla), Ocotillo (Fouquieria splendens), Sotol

(Dasylirion leiophyllum), Torrey’s Yucca (Yucca treculiana), and Eve’s Needle (Yucca faxoniana) occurring mainly on rocky slopes, interspaced with grasses, such as Black Grama

(Bouteloua eriopoda), and Arizona Cottontop (Digitaria californica). The various alliances and combinations of these plant species along with variable geologic features provide a large variety of microhabitats for vertebrate species, including B. subocularis. The average annual precipitation in IMRS is typically 235 mm, with most rainfall (70 %) occurring during the summer monsoon season (June to September). The annual average temperature for the area near

IMRS headquarters is about 18° C (De La Cerda-Camargo, 2011).

Snake Procurement. –The study was commenced in July 2009 and spanned into August 2011.

During this time, six Trans-Pecos Rat Snakes (three males and three females) were caught by hand opportunistically during evenings of the warm months (20:00 to 24:00 h). Individuals were caught mainly by coming upon them on unpaved roads, and in habitats such as rocky and alluvial

12 slopes. In the span of the first monitoring period (July 2009 to June 2010), two adult males and two adult females were radiotracked. In the second monitoring period (June 2010 to August

2011), one adult male and one adult female were radiotracked. Once a snake was found, it was transported to the IMRS headquarters for processing. The following data was taken during the processing of the snakes: SVL (snout-vent length), TL (tail length), mass (measured to the nearest tenth gram). Sex was determined by cloacal probing. All snakes were marked with a PIT-

Tag, to allow quick identification of individuals. Transmitter implantation required selecting adult individuals who met the size criteria due to dimension of the transmitters (> 100 g).

Transmitter Implantation Surgery and PIT-Tagging. – Transmitters were implanted following the methods described by Reinert (1992), with modifications suggested by Hardy and Greene

(1999). Implant surgeries were performed by Vicente Mata-Silva, a UTEP colleague who was well experienced in the procedures. A short description covering the procedures of PIT-tagging, used for later identification, and surgical procedures are as follows.

Prior to PIT-tagging and transmitter implantation, each snake was weighed in a plastic container, examined for external parasites, and measured for SVL and TL. Following this, snakes’ were guided into a transparent plastic restraining tube to a depth of about one-third their body lengths for stability and to guard against potential bites. The posterior two-third portions of snakes’ bodies were seized and held by hand during PIT-tagging and transmitter implantation surgeries; sexes were determined by using a sterile probe. Once body measurements were taken,

PIT-tags were inserted sub-dermally into right dorsolateral sections previously disinfected with

70% ethanol, ca. 20 cm from cloacae using a sterile PIT-tagging syringe (Fig. 6). After implantations, liquid antiseptic bandages (New-Skin©) were applied to the small needle

13 punctures to induce healing and prevent infection. The tubed snakes were then placed on a sterilized table and positioned anteriorly into an anesthesia chamber for general inhalation using liquid isoflurane (1 to 2 ml). Cotton was placed between the tubed snakes and walls of the chamber to minimize release of excess gas into the laboratory room. Anesthesia was dispensed from a syringe into cotton mass located in the chamber directly in front of snakes’ heads. Prior to surgeries, the transmitters (SB2, 5g; Holohil Systems Ltd.; Fig. 7), along with clean surgical instruments were placed in sterilizing solution (benzalkonium chloride) for a minimum of one hour.

FIG. 6. Passive Integrative Transponder (PIT-tag; Avid Inc.) used to identify snakes (2.1 mm in diameter, 15.0 mm in length).

The surgery lasted from 10 to 15 minutes. After snakes were anesthetized, a wide area of skin was prepared around incision sites using a Betadine solution. 1 cm longitudinal incisions were made into the snakes’ peritoneal cavities on right sides of their bodies about one-third body length from their vents; transmitters were implanted into the cavities (Fig. 8). Antennas were then inserted subcutaneously between scale rows two and three anterior to the transmitters, using fine bore brass tubes that were removed through small incisions placed a distance slightly greater than the antennas’ length from transmitters. Finally, transmitter incisions were closed in a single layer via suturing. After surgeries, snakes were removed from the anesthesia chamber, which

14 was immediately taken outside lab into the open air for complete ventilation. During awakening periods, snakes remained in plastic tubes while being observed for adequacy of respiration and circulation. Once normal breathing and strong visible muscle tones were witnessed, snakes were returned to storage containers and kept warm (between 25° and 30° C). After being frequently monitored for several hours, snakes were then returned to original capture sites and released. A week later, snakes were re-located and then radio-tracked using R-1000 telemetry receivers and

RA-150 Yagi type directional antennas (Communicational Specialists, Inc.). Data taken included: snake identification, observation number, observer, date, time, GPS location using a

Magellan Triton 400, elevation, movement (distance and direction), temperatures of snakes, ground, and air, snake posture (if observed), and any noticeable behavior, and a description of habitat and microhabitat at observation site. All statistical analyses were performed using SPSS

Version 19 (SPSS Inc., 2010).

FIG. 7. SB-2 Transmitter (5 g) implanted into body cavity of B. subocularis (Holohil Systems

Ltd.)

FIG. 8. X-ray depicting the typical location of the implantation of a temperature-sensitive transmitter in a Mojave Rattlesnake (Crotalus scutulatus). Note the antenna running laterally under the snake’s skin (from http://www.holohil.com/snake.htm).

Movement and Home Range. - Daily movement was determined as straight-line displacement between subsequent locations, and divided by the number of days between those relocations. Average daily movement rates were calculated for each month during the active season and analyzed for differences between individual snakes using ANOVA (Beaupre, 1995).

Home ranges were obtained using minimum convex polygons (MCP, ha) (Jennrich and

Taylor, 1969). Hawk’s Tool Analysis was used to determine core areas where snakes spent 50 % of their time (50% kernels) (Beyer, 2004. http://www.spatialecology.com/htools). Current studies investigating home ranges of animals normally use least square cross validation (LSCV), a parameter within which allows smoothing of the bandwidth of the kernel contours. Due to the

16 many physiological and ecological limitations of reptiles, this method may produce the depiction of the sizes of home ranges of individuals as inconsistent (Row and Blouin-Demers, 2006;

Downs and Horner, 2007). Thus, problems overestimating home ranges in reptiles due to the shading factor can lead to inaccurate portrayal of home range size, which can lead to difficulty comparing it with other snake studies (Row and Blouin-Demers, 2006). This study will only use the recommended methods by Row and Demers (2006) using minimum convex polygons

(MCPs) as the ideal method in determining the home range of reptiles. A Mann-Whitney t test was used to see if there is a difference between MCP sizes, and 50 % kernel sizes of individual.

Habitat and Microhabitat. – Habitats selected by snakes were identified following four topographic characteristics of the terrain, and include rocky and alluvial slopes, alluvial flats, and arroyos. Plant associations were classified according to Escamilla (2012) (see below). Once a snake was located, the microhabitat type was determined by identifying percentage of the different ground cover components in a square meter centered on the position of the snake

(Reinert, 1984). Recognized ground cover components included the structural elements of vegetation, rocks, gravel, sand, alluvium, and plant litter. In this study, however, ground cover elements such as sand and alluvium were not used. Microhabitat structure was determined by the physical characteristics of the diurnal refuges of B. subocularis. The five recognized microhabitats in the study included: in crevice (a geologic fissure in rocky structures), in burrow

(circular, mammal refuge), under vegetation litter (decomposing organic plant matter on surface), under rocks, and under live shrubs (e.g., Sotols, Agaves, Yuccas, and Prickly Pear

Cacti). A photograph of each microhabitat site was taken every time a snake moved to a new location.

17 Geographic positions of snakes were plotted on a digital vegetation/habitat (VH) map to determine if there was a pattern between snake movements and the distribution of different classes identified in the study area. The GIS map containing a total of 11 VH classes was developed by Rebecca Escamilla in UTEP’s System Ecology Laboratory, which reflects geographic variation in large scale environmental structure (Escamilla, 2012). The 11 classes were numbered according to the association generated by the GIS map of IMRS. VH classes are as follows: 1 = Shadow (undetermined association), 2 = Bare Ground, 3 = River, 4 = River

Riparian, 5 = Yucca/Grassland/Mixed Scrub, 6 = Bouteloua scrub, 7 = ABV

(Agave/Bouteloua/Viguiera) Scrub, 8 = Larrea/Acacia, 9 = Larrea Shrubland, 10 = Tanks and 11

= Arroyo. River (3) and River Riparian (4) classes were not used in this study because they do not occur on IMRS proper. Chi square tests (X2) were used to analyze habitats and microhabitats frequencies.

Selected sites vs. Random sites. – 172 sites selected by Trans-Pecos Rat Snakes were compared to 172 random sites to substantiate if individual snakes preferred sites within home ranges based upon microhabitat characteristics. UTM coordinates were utilized in determining random sites, generated by a random distance (10 – 200 m) and the eight cardinal directions as a random bearing using Random.org (http//www.random.org). One-time locations by snakes were included only once in the analysis, and sites in which snakes were active were excluded (Blouin-

Demers and Weatherhead, 2001). Selected sites were compared with random sites using

MANOVA with repeated measures and Wilk’s lambda to test for significant difference.

Radiotelemetry and Thermoregulation: Active and Overwintering Periods – Six Trans-Pecos

Rat Snakes were monitored from July 2009 to August 2011. In that time frame, the monitoring of

18 thermoregulation was measured in the active season (warm months) and inactive season (winter period). The SB-2 radio transmitters used in the study (Fig. 3) were temperature-sensitive, and functioned by the emittance of pulses proportional to temperature (frequencies ranged between

138 and 235 MHz). Radio transmitters had specific calibration curves supplied by the manufacturer (pulse rates ranged between 0° C to 45° C in 5° C increments). During the active period (May through October), all six B. subocularis were monitored after they left their hibernacula (egress) until they again entered their site of winter dormancy (ingress). The active period during warm months was determined as the phase during which snakes were active in their environment during hours of darkness, because B. subocularis is nocturnal. Individuals were monitored while in or near their diurnal refuges; data recorded included: date, time, geographic location, temperature (body, ambient, substrate, and microhabitat), and any observed behavior. Body temperature data was acquired by recording time intervals between eleven continuous signals emitted by the temperature-sensitive transmitters. Average body temperatures per month as well as per individual were analyzed with paired sample t tests with Bonferroni adjusted probabilities. As soon as the ingress date was determined (no movement to a new place), snakes were monitored there during the overwintering period.

Only five B. subocularis were monitored during the winter period (November through March) from 2009 – 2010, and 2010 -2011. Early in the study, a male was killed by a predator on August of 2009, so it was not included in this section because it died before entering its winter refuge.

Therefore, two females and one male (winter 2009-2010), and one male and one female (winter

2010-2011) were monitored.

19 Winter body temperature readings were measured at the snakes over-wintering sites using the same approach as during the active season. However, MP3 digital voice recorders (Olympus ®) were used to obtain body temperature data continuously for the 12 to 24 hours when the investigator was not present. For the active season as well as the winter periods, parametric (t test) and non-parametric (Chi square) statistical tests were employed. Average body temperatures per month as well as per individual were analyzed with paired sample t tests with

Bonferroni adjusted probabilities.

20 RESULTS

Movement and Home Range.-From July 2009 to August 2011, five snakes were radiotracked on IMRS during the active season for time periods ranging from 22 to 408 days (Table 1).

Snakes emerged from their winter refuges during late April/early May (data for the month of

April was included with May, as only two individuals for that month were observed on the last day [30 April]), and returned to their overwintering sites in late October and early November

(Figure 9). The home ranges of the five Trans-Pecos Rat snakes are depicted in Appendix 1. The largest home range was attributed to a male, individual 04 (123.6 ha, Table 1, Appendix 1-E), followed by individual 02 (female, 92.1 ha, Table 1, Appendix 1-C). The other home range data for the snakes are as follows: individual 05 (male, 30.7 ha, Appendix 1-F), individual 03 (female,

26.5 ha, Appendix 1-D), and the individual with the smallest home range, individual 01 (female,

20.9 ha, Appendix 1-B). Home ranges for all individuals averaged 58.8 ha and ranged in size from 20.9 to 123.6 ha. By sex, mean home ranges were 46.5 ha (n = 3) for females and 77.2 ha

(n = 2) for males (Table 1). Of the five individual snakes in the study (IDs 01-05), the mean total movement was 6161.8 m (females= 6692.3 m, males=5366.3 m; Table 1).

The 50% kernel sizes within the home ranges of B. subocularis were profoundly smaller in size as opposed to the minimum convex polygons (MCP). The difference between the minimum convex polygons and the 50% kernels sizes (in ha) was statistically significant (W = 40.0, p <

0.01). In all, the total successive distances that Trans-Pecos Rat Snakes traveled were 31,761.2 m. Movements ranged from 0 to 1746 m. By sex, females traveled a total of 20076.7 m, and males traveled 11686.5 m. in successive movements. The greatest distance traveled in one

21 successive movement was by a male (individual 04, 1746 m). There was a significant difference in total movements traveled (m) between the sexes (t = 8.2, df = 172, p < 0.01).

By month, snakes displayed the highest total average movement in June (x¯ = 308.5 m; ♀ =

277.5 m, ♂ = 343.6 m), followed by July (x¯ = 203.3 m; ♀= 173.8 m, ♂= 270.7 m) and May (x¯ =

197.8 m; ♀ = 276.8 m, ♂ = 88.4 m). The months of September (x¯ = 186.9 m; ♀ = 209.5 m, ♂ =

157.7 m), October (x¯ = 117 m; ♀ =113.8 m, ♂ = 124.2 m), and August (104.1 m; ♀ = 276.8 m;

♂ = 88.4 m) registered the lowest movement for all snakes (Fig. 9). There was no significant difference in total average monthly movement patterns (F= 1.9, p= 0.08). The average daily movement for all snakes was 17.3 m/day (Table 1). Mean daily movement between sexes showed that females moved more frequently (18.4 m/d) than males (14 m/d). Individual mean daily mean movement (mean m/day) ranged from 12.4 to 19.6 m/d. There was also no significance between daily movement rates by month (F = 3.0, p = 0.11), however, there was a difference in daily movement rate between the sexes (t = 6.3, df = 11, p < 0.01). Snakes traveled the greatest mean distance by day during the month of May (19.3 m/d; ♀ = 21.9 m/d, ♂ = 16.6 m/d), followed by July (15.1 m/d; ♀ = 14.8 m/d, ♂ = 15.3 m/d), June (12.5 m/d; ♀ = 17.9 m/d, ♂

= 7.1 m/d) and August (11.7 m/d; ♀ = 13.3 m/d, ♂ = 10.1 m/d) (Fig 10). The months of

September (8.6 m/d; ♀ = 5.3 m/d, ♂ = 11.8 m/d) and October (4.9 m/d; ♀ = 5.7 m/d, ♂ = 4.0 m/d) had the lowest distanced traveled by day (Fig. 10). There was a positive relationship between snake total body length (TBL) and MCP home range size (ha), however, there was no statistical significance between them (R2 = 0.36, p = 0.29, Fig. 11).

22 TABLE 1. Home range (MCP) and movement patterns of six B. subocularis in IMRS. (Crosses denote the death of individual 06 early in the study) (Total m and mean daily movement rate reflects data for the snakes’ active season).

Mean daily Kernel (50%) Tracked movement ID Sex MCP (ha) (ha) days Total m rate

1 ♀ 20.9 0.000004 386 7557.1 19.6

2 ♀ 92.1 0.000006 408 7418.3 17.5

3 ♀ 26.5 0.000004 280 5101.3 18.2

4 ♂ 123.6 0.000009 407 7588.8 18.6

5 ♂ 30.7 0.000004 336 3143.7 12.4

6 ♂ † † 84 954 ------

FIG. 9. Mean total distance traveled in meters by five Bogertophis subocularis (n = 173) by month on IMRS during the active season. Bars denote standard error. Numbers in boxes are means.

FIG. 10. Mean daily distance traveled in m by sex for five Bogertophis subocularis (n = 173) by month on IMRS during the active season. Lines with circles are females, and lines with triangles are males.

FIG. 11. Relationship between body size (total body length; TBL) and annual minimum convex polygons (MCP) home range size for 5 adult Trans-Pecos Rat Snakes (Bogertophis subocularis) at IMRS.

25 Habitat and Microhabitat. - Four habitats that B. subocularis utilized were identified in the study (Fig. 12). The most recurrent habitats in descending order were: rocky slopes with 74 observations (43 %), followed by alluvial flats (n = 43, 25 %), alluvial slopes (n = 32, 18 %), and arroyo habitats (n = 24, 14 %) (Fig. 13). The distribution of habitats selected by all snakes was statistically significant (X2 = 30.9, df = 15, p < 0.05). By month during the active seasons, snakes

FIG. 12. Photographs of identified generalized habitats used in the study that snakes were observed. Clockwise from top left: rocky slope, alluvial flat, alluvial slope, and arroyo.

FIG. 13. Habitats utilized by B. subocularis at IMRS during the active season (n = 173 observations). Numbers in boxes reflect number of observations.

FIG. 14. Monthly habitats utilized by B. subocularis on IMRS during the active season (n = 173 observations). Bar patterns indicate: filled = rocky slopes, non-filled = arroyos; diagonal = alluvial flats; checkered = alluvial slopes.

27 were mostly associated with rocky slopes in May (7.5 %), June (9.8 %), and October (12.7%).

Snakes mostly inhabited alluvial flats in the month of August (8.7 %) (Fig. 14).

TABLE 2. Frequency and percentage of microhabitats utilized by B. subocularis at IMRS.

Microhabitat Observations Percent in crevice 17 10

in burrow 34 20 under rocks 35 20 under shrub 62 36 under plant litter 25 14

TOTAL 173 100

Five microhabitats were identified in which snakes were located. Of these diurnal retreats, snakes were mostly found under shrubs (36 %), followed by under rocks (20%), and in burrows

(20%), with lesser occurrences under plant litter (14%), and in crevices (10%) (Table 2). The distribution among those observations was highly significant (X2 = 49.2, df = 20, p < 0.01).

Regarding the under shrub microhabitat, snakes found under Sotols (45 %) and Yuccas (25 %)

28 accounted for most of the observations. In all, snakes revisited the same microhabitats 26 % of the time during the active season. Of these microhabitats, shrubs (36 %) (mostly Sotols) were revisited the most.

FIG. 15. Ground cover composition (%) of microhabitats utilized by B. subocularis (n = 173 observations). Bars denote standard error.

In regards to percent of microhabitat ground cover, vegetation was the most represented (41

%), followed by rocks (30 %), plant litter (20 %), and gravel (9 %) (Fig. 15). While vegetation was the main ground cover component snakes utilized by month, the other variables shifted in usage. Rocks appeared as the main component in the month of June (42 %), albeit with vegetation trailing slightly (40 %). Rocks again appeared as the most dominant component in the

29 month of October (Fig. 15). Other components such as plant litter were the main component during the month of July (36 %), and gravel remained, for the most part, the least important ground cover component throughout the activity season (Fig. 16). Results for the MANOVA for comparison between 172 snake sites and 172 random sites was statistically significant (Wilk’s Λ

= 0.8, F = 20.2, p < 0.01).

FIG. 16. Mean percentage of ground cover (by month) of microhabitats utilized by B. subocularis during the active period. Bars denote standard error. Symbols represent the structural components of microhabitats (squares = vegetation, filled circles = gravel, filled triangles = plant litter, and exes = rocks).

30 TABLE 3. Frequency and percentages of vegetation classes observed for snakes at IMRS (n = 173 observations).

Vegetation Class (VH) Frequency Percent (%)

Shadow 34 20

Bare Ground 12 7

Yucca/Grassland/Mixed Scrub 56 32

Bouteloua Scrub 6 4

Agave/Bouteloua/Viguiera (ABV) 30 17

Larrea/Acacia 15 9

Larrea Shrubland 11 6

Tanks 3 2

Arroyo 6 4

TOTAL 173 100

The overlay of land cover arrangement comprising 11 vegetation classes demonstrated that snakes were most frequently observed in the classes identified as Yucca/Grassland/Mixed Scrub,

Shadow, and Agave/Bouteloua/Viguiera (32 %, 20 %, and 17 %, respectively) (Table 3).

Although other vegetation classes tallied observations less than 10 %, Larrea/Acacia, Bare

Ground, and Larrea Shrubland were similarly partitioned (9 %, 7 %, and 6 %, respectively).

Vegetation classes consisting of Bouteloua scrub (4 %), Arroyo (4 %), and Tanks (2 %)

31 represented the least frequented communities selected by snakes (Table 3). The distribution among these observations was highly significant (X2 = 78.4, df = 40, p < 0.01).

Radiotelemetry and Thermoregulation: Active Periods. – Mean body temperatures (Tb) for all snakes during the active season was 28.7° C. (Fig. 17). The lowest body temperature was that of a female, at 17.7° C (ID 03) during the month of October; and the highest body temperature reading was 34.8°C (ID 01), another female during the month of August. By sex, females had an average Tb of 28.6° C (Fig. 18), while males had a similar Tb profile, albeit slightly higher (x¯ =

29° C, Fig. 19). By sex, although Tb were similar during the active season, females’ Tb were more variable than males (t =-0.6, df = 170, p < 0.01).

By month, snakes achieved the highest mean Tb during the month of July (31.8° C), and registered the lowest mean Tb in the month after egress (May, 25.8° C) (Fig. 20). Differences in

Tb during the months of the active season was statistically significant (t = 60.4, df = 164, p <

0.01). The distribution among Tb and the months of the active season was statistically significant

2 (X = 438.3, df = 385, p < 0.05). When comparing Tb and other environmental variables (Ta = ambient temperature, Ts = substrate temperature, and Tmicro = microhabitat temperature), Tb was found to be statistically significant over all variables: Tb vs Ta (t = -3.4, df = 172, p < 0.001), Tb vs Ts (t = -3.3, df = 172, p < 0.01) and Tb vs Tmicro (t = 2.6, df = 172, p < 0.05). By month, Ta and

Ts were closely correlated, in which the two variables are almost parallel to each other in the active season (Fig. 21). Microhabitat temperatures (Tmicro) were the most shifting, while body temperatures, for the most part, ranged below Ta and Ts, and were generally higher than microhabitat temperatures (Fig. 21).

FIG. 17. Box plot of mean Tb of B. subocularis during the active season (n = 173 observations).

FIG. 18. Box plot of mean Tb of female B. subocularis during the active season (n = 107 observations).

FIG. 19. Box plot of mean Tb of male B. subocularis during the active season (n = 66 observations).

FIG. 20. Tb profile of B. subocularis during the active season by month. Bars denote standard

error and numbers in boxes are average temperatures.

FIG. 21. Mean values of temperature variables (Tb = body temperature, Ta = ambient temperature, Ts= substrate temperature, and Tmicro = microhabitat temperature) of snakes by month during the active season.

Radiotelemetry and Thermoregulation/Overwintering Sites: Winter Period. - A total of five

Trans-Pecos Rat Snakes were radiotracked during the winter periods of 2009-2010, and 2010-

2011. The average number of days in which snakes resided in their respective overwintering sites was 172.5 days (Table 4) (data for individual 04 is not included due to the fact that the snake was not found during the period of the ingress).

A total of 2445 observations were recorded in respect to body temperatures during the winter months. Mean body temperatures (Tb) for B. subocularis during the winter period was 15.3° C

(Fig. 22). By sex, females attained a mean body temperature of 15° C, while males Tb was slightly higher, at 15.8° C (Fig. 23), in which there was a significant difference between the sexes (t = -3.1, df = 2443, p < 0.01). The span of body temperatures ranged from 2.3° C to 26.5°

C for all snakes. By sex, Tb ranged from 2.3° C to 26.5° C for females (n = 1793), and 13.3° C to

18.5° C for males (n = 652) (Fig. 23, Table 5). Tb for individual Trans-Pecos Rat Snakes was statistically significant (X2 = 8234.9, df = 96, p < 0.01).

TABLE 4. Overwintering characteristics of five B. subocularis on IMRS during the winters of

2009-2010 and 2010-2011. * denotes the lost individual during the ingress date range.

ID Sex TBL (mm) Ingress date Egress Date Total days Winter Period 1 ♀ 1190 24-Oct-2009 1-May-2010 176 2009-2010 2 ♀ 1170 24-Oct-2009 1-May-2010 176 2009-2010 3 ♀ 1070 11-Nov-2010 30-Apr-2011 170 2010-2011 4 ♂ 1300 * 1-May-2010 * 2009-2010 5 ♂ 1260 13-Nov-2010 30-Apr-2011 168 2010-2011 Average 1198 172.5

36 Initially at the start of the winter period, monthly mean Tb saw a dramatic fall after the ingress

month (November), and displayed a similar distribution of body temperatures in the following

months (Fig. 24). By month, November attained the highest mean Tb during the winter period

(23.2° C), while January recorded the coldest mean T b (12.2° C). After the month of November,

the mean Tb during the winter period was similarly distributed during December, January,

February, and March (13.2° C, 12.2° C, 13.2° C, and 14.3° C, respectively) (Fig. 24). After

January, the months following had a gradual, although slight, rise in mean Tb (Fig. 24).

2 Differences in average Tb for all individuals per month was statistically significant (X = 7889.8,

df = 96, p < 0.01).

TABLE 5. Body temperatures of five individual B. subocularis during the winter periods of

2009-2010 and 2010-2011.

Sex Females Males Mean Minimum Maximum Total N Mean Minimum Maximum Total N ID 01 Tb 26.3 26.0 26.5 277.0 . . . .0 02 Tb 15.5 12.5 20.9 1005.0 . . . .0 03 Tb 8.0 2.3 15.0 511.0 . . . .0 04 Tb . . . .0 18.1 18.0 18.5 257.0 05 Tb . . . .0 14.3 13.3 15.0 395.0

FIG. 22. Box plot of Tb during the two winter periods of five individual B. subocularis at IMRS.

Bars denote standard error (n = 2445 observations).

FIG. 23. Box plots of Tb of female and male B. subocularis during the two winter periods at

IMRS. Bars denote standard error.

FIG. 24. Mean winter Tb profile by month of B. subocularis at IMRS. Bars denote standard error

(n = 2445 observations). Number in boxes are means.

39 During the winter periods, all individual snakes displayed a general stability in mean Tb by hour during 00:00 to 14:30 h ( 15° C), then abruptly rising in Tb during 14:30 to 17:30 h time frame ( 15° C to 23° C) (Fig. 25). After this time frame, Tb again returned to the 15° C for the rest of the time.

FIG. 25. Mean daily Tb of B. subocularis (by hour) during the two winter periods at IMRS. Bars denote standard error (n = 2445 observations).

FIG. 26. Mean daily Tb of B. subocularis (by hour) during the two winter months of November on

IMRS (n = 510 observations).

FIG. 27. Mean daily Tb of B. subocularis (by hour) during the two winter months of December on

IMRS (n = 763 observations).

41 By months, mean Tb varied by hour. In the ingress month (November, n = 510), the Tb profile had a disjunct distribution. The mean Tb for November was 23.2 °C, however some jumps

(maximum Tb = 26°C; 10:00 to 15:00 h), and drops (minimum Tb = 19° C; 17:00 to 18:00 h)

(Fig. 26) were shown during the daily period. During the month of December (n = 763), most observations were within the 13° C range, with only a few observations dropping below 10° C

(14:00 to 14:30 h; Fig. 27) and with only one mean Tb observation at a higher average (15° C,

16:30 h) (Fig. 28).

The mean hourly Tb for January (n = 509) was characterized by a highly contrasting rising and falling relationships (Fig. 28). Tb stayed within the 10° C range (00:00 to 08:00 h) then rose sharply, tapering off at approximately 16° C in the 10:00 to 13:00 h time frame. A small drop

( 15°C; 14:30 to 15:00 h) and another sudden rise ( 18°C; 17:00 to 18:00 h) followed; with Tb returning the 10° C range after 18:00 h (Fig. 28). The mean hourly Tb for the month of February

(n = 267) appeared to display the most stable body temperatures compared to the other months.

Tb ranged mostly within 13° C range, with only few observations (mostly early morning or late afternoon) ranging between 12° C and 14° C (Fig. 29). During the month of March (n = 395), the mean hourly Tb typically stayed in the 14° C range, with some observations (early to mid- morning and late afternoon) ranging from 13° C to 15° C (Fig. 30).

FIG. 28. Mean daily Tb of B. subocularis (by hour) during the two winter month of January on

IMRS (n = 509 observations).

FIG. 29. Mean daily Tb of B. subocularis (by hour) during the two winter month of February on

IMRS (n = 267observations).

FIG. 30. Mean daily Tb of B. subocularis (by hour) during the two winter month of March on

IMRS (n = 395observations).

Individual Trans- Pecos Rat Snakes overwintered independently in IMRS. Overwintering sites were mostly composed of rocks, and had a mean elevation of 1317.2 m. The highest overwintering site was that of individual 03 (female) that overwintered at a site 1358 m in elevation, beneath a large rock near a northeast facing cliff. Snakes that had the largest home ranges (IDs 02 and 04, female and male respectively); overwintered underneath rocks on rocky slopes located in relatively large canyon areas far (> 1 km) from their normal summer ranges.

Another snake (ID 02) overwintered underneath a rock, on a rocky slope facing northwest (elev.

1287 m); while individual 05 selected an overwintering site underneath a rocky on a slope also facing northwest (elev. 1345 m). Individual 01 overwintered underneath rocks on a west facing

44 cliff ledge (1319 m), and individual 05 overwintered underneath loose rocks on a rocky slope facing west that was almost devoid of vegetation (1277 m elev.). Snakes 01, 03, and 05 all overwintered on different slopes of Flat Top Mountain (30º 44’20”N, 104º 59’35”W) (Fig. 31).

The structural compositions of overwintering sites were mostly rocks (86 %), followed by the lesser represented vegetation (8 %), gravel (4 %), and litter (2 %) microhabitats.

45 DISCUSSION

Movement and Home Range. – All Trans-Pecos Rat Snakes in this study were active approximately six months per year, with individual snakes abandoning their overwintering sites in late April or early May. Home ranges of all B. subocularis overlapped to some degree in the vicinity of Flat Top Mountain (Fig. 31). The species on IMRS is primarily nocturnal, although one individual (ID 03) was observed three times, once as it was actively foraging at 9:00 h, on 15

August 2010, and twice partially exposed at different sites within crevice retreats. The first of those two observations was at 1800 h on 28 August 2010 high on a north-facing rocky cliff with the lower third of its body exposed. It was later observed partially exposed on 27 November

2010 at 10:30 h outside the entrance to its winter retreat (Fig. 32). Thus, even though B. subocularis is strictly considered night active as indicated by Rhoads (2008), Sawyer (1993), and

Sawyer and Baccus (1996), on IMRS it still occasionally exposes itself during daylight hours when conditions allow, especially during late summer through early winter.

The activity period is comparable to other North American colubrids inhabiting southern temperate latitudes in North America (Ernst and Ernst, 2003), and very similar to the Green Rat

Snake (Senticolis triapsis) in Arizona (Radke and Malcom, 2008).

Bogertophis subocularis on IMRS, on average, had large home ranges sizes, with a mean of

58.8 ha in area; all snakes reduced their movement rates during the latter months of the active season. Males had substantially larger home ranges (x¯ = 77.2 ha) than females (x¯ = 46.5 ha).

Bogertophis subocularis in this study during the active period traveled greater distances from

46 one diurnal retreat site to another (1746 m; ID 04) than that reported for the same species by

Sawyer (1993) and Sawyer and Baccus (1996) (812 m). This is probably due to the modifications in those previous studies where all snakes were originally released at one common site, thus the foreign landscape may well have hindered snake movements. In the present study, the large home range sizes for B. subocularis was analogous to other populations of large North American colubrids, such as the Pine Snake (P. melanoleucus) (x¯ = 59.9 ha, Gerald et al., 2006; x¯ = 59.2 ha, Miller, 2008); Coachwhip Snake (M. flagellum) (x¯ = 70.4 ha, Johnson et al., 2007; x¯ = 60.4 ha, Mitrovich et al., 2009; x¯ = 85.3 ha, Dodd and Barichivich, 2007; x¯ = 53.4 ha, Secor, 1995); smaller than the Indigo Snake (Drymarchon couperi) (x¯ = 305.5 ha, Hyslop, 2007; x¯ = 185.3 ha,

Dodd and Barichivich, 2007); and larger than the Racer (C. constrictor) (x¯ = 24.2 ha, Carfagno and Weatherhead, 2008; x¯ = 12.2 ha, Plummer and Congdon, 1994), Gopher Snake (P. catenifer)

( x¯ = 31.7 ha, Kapfer et al., 2010) and the Great Plains Rat Snake (P. emoryi) (x¯ = 10.2 ha,

Sperry and Taylor, 2008).

FIG. 31. Flat Top Mountain, a distinctive mesa and ridge system containing rocky slopes that harbored overwintering sites for most B. subocularis studied herein. Snakes move downward to other habitats during the activity season.

FIG. 32. Typical overwintering site of female B. subocularis (ID 03), partially exposed outside its overwintering site.

48 In all large North American colubrid snakes, especially those within the Lampropeltini group, the Black Rat Snake (P. obsoletus) is the most represented species in radiotelemetry studies. In regards to home range, however, P. obsoletus occupies significantly less area than B. subocularis

(x¯ = 5.6 ha, Carfagno and Weatherhead, 2008; x¯ = 9.5 ha, Durner and Gates, 1993; x¯ = 15.2 ha,

Blouin-Demers et al., 2007; x¯ = 35.1 ha, Sperry and Weatherhead, 2009). This is unusual in the sense that normally, home range size is proportional to the body size of the species.

Pantherophis obsoletus is the largest of the New World rat snakes (Schulz, 1996). It was thought that its contact with and success in anthropogenic produced fragmented areas (Durner and Gates,

1993; Schulz, 1996), and differences in feeding and locomotion strategies, such as arboreality

(Sperry and Weatherhead, 2009) lead to a small home range for such a large-bodied snake.

Arboreal behavior is a vertical scale that brings another variable into home range studies of snakes. Greenberg and McClintock (2008) suggested utilizing terrain modeling in spatial ecological studies to add a third-dimensional approach in calculating home ranges of snakes.

Pantherophis obsoletus is known to readily climb trees in search of birds, one of their major prey items (Fitch, 1963; Schulz, 1996). In southeastern U.S. populations of P. obsoletus, snakes have been observed to show preference for climbing behavior (Jackson, 1976) to allow greater inclination for selecting arboreal niches. The species utilized elevated sites at more than half of all observations in a population in Maryland (Durner and Gates, 1993). Given that P. obsoletus has a large geographic distribution and occupies habitats that are more mesic (associated with woodlands and forests), terrain modeling is probably not as applicable to B. subocularis spatial studies because it uses a much less complex Chihuahuan Desert landscape. Bogertophis subocularis is known to show arboreal behavior (Pauly and LaDuc, 2009), although the instances occurred in ecotonal habitats or along water courses within the Chihuahuan Desert. Individual

49 Trans-Pecos Rat Snakes were observed climbing shrubs in the present study, some of which reach impressive size (e. g., Y. faxoniana and P. glandulosa), but due to lack of spatial abundance of large shrubs, terrain modeling techniques would probably not add much to home range size. Still, large shrubs seem to be important to the natural history of Trans-Pecos Rat

Snakes on IMRS.

Home range sizes and 50% kernel sizes (core areas) of Trans-Pecos Rat Snakes in the present study varied more in the males than females. Also, B. subocularis traveled within relatively large geographic areas in their home ranges, but utililized smaller core areas most often. This pattern also transpires in other large North American colubrids (Johnson et al., 2007). Concerning sexual differences, male B. subocularis had larger home ranges than females, which is also commonly observed in other large North American colubrids (Gerald et al., 2006; Kapfer et al.,

2010; Hyslop, 2007; Dodd and Barichivich, 2007; Johnson et al., 2007; Mitrovich et al., 2009;

Dodd and Barichivich, 2007; Secor, 1995).

In relationship to southwestern species of rattlesnakes (genus Crotalus), the large home ranges of B. subocularis in this study were greater than those of C. atrox (x¯ = 5.4 ha), C. molossus (x¯ = 3.5 ha), C. tigris (x¯ = 3.5 ha) (Beck, 1995) and C. cerastes (x¯ = 3.48 ha; Secor,

1995). Bogertophis subocularis similarly occupied larger home ranges and subsequently traveled greater distances than the much smaller and sympatric Rock Rattlesnakes (C. lepidus) on IMRS (x¯ = 13.7 ha; Mata-Silva, 2011). The mean home ranges of B. subocularis in this study area was also larger than other rattlesnakes occurring outside the desert southwest, such as C. adamanteus (48.3 ha, Waldron et al., 2006; 25.6 ha, Hoss et al., 2010) and C. horridus (29.1 ha,

Waldron et al., 2006). Perhaps large colubrid species possess physiological and ecological

50 adaptations that allow them to occupy larger home ranges than rattlesnakes. Both groups are primarily predators of vertebrates, so feeding behavior may affect ecological factors within respective environments such as abundance, unevenness, and renewal rates related to those resources (Pough et al., 2004). Feeding behavior in large colubrids, such as rat snakes, involve active predation that leads to foraging movements culminating in large home ranges. This is unlike many venomous rattlesnakes, which are more sedentary ambush predators with more localized movement patters, and thus, have smaller home ranges. Factors such as an increase in energetic requirements for predators control home range size in some lizards (Perry and Garland,

2002). Gila Monsters (Heloderma suspectum), have one of the highest VO2 max of any lizard, and it is interesting to note that home ranges for that species are as large as found in members of the whipsnake genus Masticophis (Beck, 1991; Beck, 2009). Racer snakes (C. constrictor) have high metabolic activity (Lillywhite, 1987), which likely influences the energetic costs of foraging and exceeds the energy consumptions of other snakes with different feeding modes (Plummer and Congdon, 1996). These factors could also apply to B. subocularis, because it occupies large home ranges where it forages widely for prey. It would be interesting to examine how the energy costs of nocturnal B. subocularis compares to that of active diurnal species of Masticophis and

Coluber.

Home range size versus movement patterns was not similar between Trans-Pecos Rat Snakes in the study area and other reported colubrid species, with two exceptions: P. emoryi (Sperry and

Taylor, 2008) and a South Carolina population of C. constrictor (Plummer and Congdon, 1994).

Bogertophis subocularis moved less frequently per day than Illinois populations of P. obsoletus and C. constrictor (Carfagno and Weatherhead, 2008) and P. catenifer (Kapfer et al., 2008), although those species inhabited far smaller home ranges. Analyses by Sawyer (1993) and

51 Sawyer and Baccus (1996) indicated that female B. subocularis moved more frequently and at a more rapid rate than males. However, both papers noted that snakes in their study were all released at one common site, and long distances from their original capture sites. In the present study, females traveled an average of 6692.3 m, which was substantially greater than males (x¯ =

5366.3 m) despite having on average smaller home ranges. This seems to indicate an inverse relationship of movement patterns between sexes during the active season. However, the greatest distanced traveled by all snakes was achieved by individual 04, a male (7558.8 m), which also had the largest home range (123.6 ha). However, individual 01, a female, trailed only slightly

(7557.1 m) and also had the smallest home range of all the snakes in the study (20.9 ha). The other male, individual 05, had a small home range (30.7 ha) and registered the lowest mean total successive movement (3143.7 m), traveling at a slower rate than the females. The large amount of variation in total distance traveled is partially explained by the daily movement rates by the sexes. Females traveled more on a daily basis as opposed to males. Observations in other North

American colubrids where females moved more frequently than males were witnessed in some populations of P. obsoletus (Carfagno and Weatherhead, 2008), in northern populations of P. catenifer (Kapfer et al., 2008; Shewchuk, 1996), and eastern populations of P. melanoleucus

(Gerald et al., 2006).

Patterns relating to movement, and subsequently seasonal patterns, are often thought to reflect reproductive activity (e.g., Glaudas and Rodriguez-Robles, 2011; Rhoads, 2008). In this study, no individuals were observed in any form of reproductive behavior. There is a general lack of information in the literature concerning the reproductive biology of B. subocularis; most information comes from captive individuals (Rhoads, 2008) with an emphasis on husbandry.

Glaudas and Rodriguez-Robles (2011) observed male Speckled Rattlesnakes (C. mitchellii)

52 traveling farther than females during the mating season. The mating season of B. subocularis is believed to happen during the mid-active season (June, July), a much later breeding period than for other North American colubrids (Rhoads, 2008). Sources also note the high incidence of individuals crossing roads beginning in the month of July (Reynolds, 1982), many of which are males supposedly seeking mates (Rhoads, 2008). Males in this study traveled further on a daily basis than females during the months of July and September (Fig. 10), but that decreased during

August, which may have been associated with rainfall patterns on IMRS; monsoon rainfall is at its peak during July (De la Cerda-Camargo, 2011), a factor that could affect reproductive behavior. The evolution of both mate-searching activities and male body size have been linked to movement patterns in snakes (Glaudas and Rodriguez-Robles, 2011), and these are likely to be influenced by energetic requirements relating to home range size (Carfagno and Weatherhead,

2008; Perry and Garland, 2002; Lillywhite, 1987; McNab, 1963). The timing of movement patterns between sexes can vary. Thus, it seems that male B. subocularis moved more frequently than females during the supposed breeding period for the species.

Habitat and Microhabitat. - Within the snakes’ respective home ranges, B subocularis in this study was mostly associated during the active season with rocky slopes. Rocky slopes were the most utilized habitat for snakes overall (43 %), starting after egress during May and June. The months of July and August saw a shift in selection to different habitats; July was characterized by a nearly equal distribution in rocky slopes and alluvial flats, and snakes during August displayed a strong selection for alluvial flats. Arroyos were the least frequented habitats (14 %), as they possibly served as avenues for snakes moving from one habitat to another. A pattern

53 emerged when snakes shifted away from rocky habitats in the mid-active season (July, August, and September) and then returned to rocky slopes at the end of the active season (October) (Fig.

14). All overwintering sites selected by snakes were located on rocky slopes. This is a clear indication that Trans-Pecos Rat Snakes in the study area used sites in which the geographic structure provided an elevation gradient (slope) and a substrate (rocks) that benefited thermoregulation, especially in the early and late stages of the active season and during winter periods (see Fig. 31).

Diurnal retreat sites of Trans-Pecos Rat Snakes during the active period were mostly found under shrub microhabitats (36 %). This result is also similar to the Rock Rattlesnake (C. lepidus), which occurs sympatrically with B. subocularis on IMRS (Mata-Silva, 2011). However, C. lepidus on IMRS were mostly present in arroyo habitats, as opposed to B. subocularis’ preference for rocky slopes. This could be explained by differences in prey preference; C. lepidus eats primarily small lizards and snakes (Mata-Silva et al., 2010; Mata-Silva, 2011; Mata-

Silva et al., 2011) as opposed to B. subocularis, which consumes mostly medium-sized rodents

(Rhoads, 2008). Also important, is the vegetation structure of the diurnal retreats. Bogertophis subocularis selected mostly shrub microhabitats, especially those containing Sotols (45 %), and

Yuccas (25 %), both of whose leaves supply needed shade for snakes during hot daytime summer temperatures. The lower, dry yellowish coloration of leaf blades in Sotols and Yuccas are somewhat similar to the general body coloration of B. subocularis, so they also supply background matching (camouflage) effects to protect snakes from potential diurnal predators.

Other microhabitats were utilized by snakes for diurnal refugia. Under rocks and in burrows were equally partitioned (20 %, respectively), and crevices were the least frequented microhabitat (10 %). Microhabitats of under rocks and in crevices has been related to Trans-

54 Pecos Rat Snakes in association with the host-specific tick (Aponomma elaphensis), which infests the end of snake’s tails in some populations of snakes (Degenhardt and Degenhardt, 1965;

Schulz, 1996, Rhoads, 2008), but it is unknown why only some populations within its geographic range are infected. That tick has not been observed on any B. subocularis on IMRS.

Under rocks and in burrows can also serve as localities for harboring prey consumed by B. subocularis. Schulz (1996), Rhoads (2008) and Degenhardt et al. (1996) mention small mammals (rodents) as prey for this species, as well as nestling rabbits (Sylvilagus audubonii;

Moon and Rabatsky, 2004), bats (Rhoads, 2008), and small lizards (Schulz, 1996; Degenhartdt et al., 1996). Dual studies in both field and laboratory conditions of Black Rat Snakes (P. obsoletus) chose ideal habitats to achieve optimal body temperatures after feeding (Blouin-

Demers and Weatherhead, 2001). Thus, inhabiting rocky habitats and under shrub microhabitats could aid B. subocularis for achieving optimal body temperatures after nocturnal foraging, and subsequent feeding activities. On IMRS, Rock Pocket Mice (Chaetodipus intermedius) and

Merriam’s Kangaroo Rats (Dipodomys merriami ) were the most frequently captured rodents and the higest proportion were found in or near rocky areas (Brewer, 2004). It is unknown what the primary diet items for B. subocularis are on IMRS, but it is assumed that those two species are important prey items for the species.

Results from the MANOVA seem to indicate that B. subocularis select microhabitats non- radomly. Vegetated microhabitats (shrubs) were the most frequently selected during the active season. It is only during the month of October, shortly before ingress that witnessed snakes opted for diurnal retreats underneath rocks. This coincides similarly with the occurrence of snakes in habitats made up of rocky slopes during the month of October. Other microhabitas, such as those

55 under litter, shifted in usage, peaking in August; burrows were frequented in high numbers with fewer drastic falls and peaks as opposed to under rocks. The ground cover composition of microhabitats closely mirror in distribution to the microhabitats selected. A parallel pattern was observed as microhabitats composed of vegetation (41 %) was of the most importance of mircohabitat component. Other components, such as rocks (30 %) and plant litter (20 %), followed suit in descending order of compositional importance, mirroring the variables in microhabitat selection (structure). Gravel (9 %), was the least representative in the ground cover of microhabitats selected, leaving components of vegetaion, rocks, and plant litter as most essential constituents in snakes choosing microhabitats.

The overlay of geographic positions generated from the VH map plotted snake locations during the entire active season falling in greater numbers under the Yucca/Grassland/Mixed scrub vegetation community (32%), with the exception of October. Shadow (20%) and

Agave/Bouteloua/Viguiera (ABV) (17%) were the next most used formations into which snake locations fell under during the entire active season. However, ABV was used nearly the same as

Yucca/Grassland/Mixed scrub and greater than the Shadow class during May, and after that,

Shadow was the second most utilized microhabitat, with the exception of October. Since snakes mostly selected shrubs for diurnal microhabitat sites, it is apparent that the

Yucca/Grassland/Mixed scrub community contains critical ecological conditions that support stands of Sotols and Yuccas. The Shadow communities were described by Escamilla (2012) as containing undetermined flora. The VH map places the Shadow communities in rocky areas on slopes where plants are sparse or absent (i.e., talus slopes). Microhabitats of under rocks, in burrows, and in crevices were probably most prevalent in Shadow areas, especially under rocks during October. It is also probable that ABV shared traits with Yucca/Grassland/Mixed scrub and

56 with Shadow areas. Arroyo habitats (4 %) were the second least utilized, therefore the Arroyo vegetation class was assumed to not contain a physical structure preferred by B. subocularis in the study area. Tank communities, the least utilized class (2 %), were normally associated with dammed arroyos (an artificial ecosystem), so they were not commonly utilized for reasons similar to arroyos. Therefore, the presence of snakes in arroyos and near tanks was most likely associated with occasional movements between preferred microhabitats within the home range of each individual. In the case of most individuals studied herein, Rattlesnake Tank and arroyos leading into it were the main areas where snakes temporarily resided.

Bogertophis subocularis in this study differed in the use of vegetation associations within microhabitats on IMRS from findings described by Sawyer (1993) Sawyer and Baccus (1996).

Mesquites (P. glandulosa) and Creosotebush (L. tridentata) were the dominant shrubs in their microhabitat communities on the western edge of the Edwards Plateau. In the present study, the most dominant shrubs were Sotols and Yuccas in a climax Chihuahuan Desert scrubland. The contact zone between the two regions (Chihuahuan Desert/Edwards Plateau) has different habitats and plant associations than those occurring on IMRS. The fact that snakes were all released in one common, albeit foreign site (Sawyer, 1993), seriously questions the validity of the diurnal microhabitat site selection on the Edwards Plateau. Homing behavior, especially after displacement, has been reported for many snakes (Pough et al., 2004). This, along with other aspects relating to movement ecology (and hence, habitat selection) also has to be taken into consideration in the findings of Sawyer (1993) and Sawyer and Baccus (1996).

Bogertophis subocularis were found in structured habitats similar to those found in Great

Plains Rat Snakes, P. emoryi (Sperry and Weatherhead, 2008). The selection of habitats also

57 plays a role in maintaining optimal body temperatures in habitats which have varying thermal gradients. Black Rat Snakes (P. obsoletus) preferred thermally taxing habitats (forests and fragmented areas) (Blouin-Demers and Weatherhead, 2001, 2002) as opposed to Gopher Snakes

(P. catenifer) occurring in more thermally stable habitats (Kapfer et al., 2008). Several large colubrid snakes frequenting habitats with elevation gradients (e. g. hills, slopes, uplands), like B. subocularis, have been reported for D. couperi, M. flagellum (Dodd et al., 2007), P. catenifer

(Kapfer et al., 2010), and P. obsoletus (Sperry and Weatherhead), 2009). Some colubrid snakes have bimodal activity patterns (movement between summer foraging and overwintering sites;

Gibbons and Semlitsch, 1987), such as a Tennessee population of Pine Snakes, P. melanoleucus, that displayed significant movement during the late spring/early summer and late summer/early fall (Gerald et al., 2006); those snakes selected a mosaic of habitat types instead of a uniform, preferred habitat type. Bogertophis subocularis also has a bimodal activity pattern, although they differ from some other temperate snake species by overwintering singly instead of in large communal dens.

Only adult B. subocularis were radiotracked, so there was no determination of juvenile movement patterns and their preference for habitats and microhabitats on IMRS. The same is true for reproductive activity, as no observations on mating and egg laying and hatching were observed. However, gravid females have been reported to lay eggs during the months of July and

August and hatch sometime between October and November (Rhoads, 2008). If so, there is a good possibility that juveniles overwinter in, or near, overwintering sites of their mothers. It is also feasible that juveniles select habitats and microhabitats more randomly than adults, as recorded for a Canadian juvenile P. obsoletus (Blouin-Demers et al., 2007). Reproductive behavior and juvenile activities await initiation of investigations on IMRS.

58 Chronobiological strategies and behaviors such as nocturnality could also be factors in movement patterns, and subsequently habitat and microhabitat selection. The relationship between nocturnal activity and foraging has been reported in Brown Treesnakes, Boiga irregularis, (Campbell et al., 2008); Prairie Rattlesnakes, C. viridis (Clarke et al., 1996); and

Desert Nightsnakes, Hypsiglena chlorophaea (Weaver, 2011). Snakes supposedly move less frequently during brighter moon phases than during darker moon phases (Campbell et al., 2008;

Clarke et al., 1996; Weaver, 2011). Boiga irregularis and H. chlorophaea had nocturnal activity levels influenced by prey availability, predator avoidance, and reduced their activity in open areas, especially during brighter moon phases (Campbell et al., 2008; Weaver, 2011). Nocturnal snakes were also reported to utilize structural cues, such as crevice morphology and substrate temperature gradients during microhabitat selection (Webb et al., 2004). All of these factors could apply to B. subocularis on IMRS, although individuals were observed during a variety of lunar phases in this study; no discrete analysis of lunar phase activity patterns of B. subocularis has been attempted.

In summary, B. subocularis seems to select vegetated microhabitats. How this applies to the all populations of the species within IMRS is still somewhat unclear because of the small sample size (n = 5) and the limited geographic area involved. Snakes radiotracked in this study were mostly located in a limited area on the western and southwestern slopes of the Indio Mountains that fall within a rain shadow, as the eastern slopes are somewhat cooler and receive a little more precipitation due to prevailing frontal systems (De la Cerda-Camargo, 2011). It would be interesting to see how B. subocularis selects microhabitats on the eastern slopes on IMRS, and to determine if there are differences in home ranges between the two areas.

59 Radiotelemetry and Thermoregulation: Active Period.- During the active season, results demonstrated that five Trans-Pecos Rat Snakes on IMRS had a mean body temperature of 28.7°

C, slightly higher than those reported by Sawyer (1993) and Sawyer and Baccus (1996) (27.5° C) from Edwards Plateau; both female (28.6° C) and male (29.0° C) Tb’s were slightly higher as separate groups. IMRS snakes achieved the highest mean Tb in the mid-active season during July

(31.8° C). The Tb profile of individuals was, on average, higher than the mean ambient, substrate, and microhabitat temperatures. The lowest mean Tb snakes achieved were during May

(25.8° C), after egress. During May, the Tb profile for snakes portrayed the inverse relationship of July; when Tb averaged lower than the mean ambient, substrate, and microhabitat temperatures. While the mean Tb logically decreased near ingress (October), it appears that the ambient and substrate temperature played a more important role in the regulation of Tb than microhabitat temperatures. Nocturnal species, such as Broad-headed Snakes (Hoplocephalus bungaroides) and Small-eyed Snakes (Cryptophis nigrescens) chose warm rocks over colder ones (Webb et al., 2004), which suggest that substrate temperatures are a determining factor in the selection of microhabitat structure. In this study, although ambient and substrate mean temperatures exhibited similar relationships, substrate temperatures could be the most important factor influencing thermoregulation of B. subocularis during nighttime hours. Snakes were found in greater frequency on rocky slopes where diurnal microhabitat sites, insolated by solar radiation and retained via conduction, offered optimal conditions for B. subocularis in regulating body temperatures and avoiding lethal temperatures. Shrubs were, for the most part, the most commonly used vegetation type during the active seasons. Ambient temperatures at IMRS may reach above 40° C in June, so shrubby vegetation may well provide the structural conditions that prevent snakes from overheating. The use of rocks as diurnal microhabitats were selected most

60 often in October, as ambient temperatures were the lowest of the active season (x¯ = 28° C). The rocky substrate more than likely retains enough heat at least during early nighttime in late fall to allow for snakes to help maintain an optimum Tb. Daytime temperatures during October and even into early November can be high enough to permit snake activity, so it is assumed that nighttime temperature is the primary cue for B. subocularis to enter their overwintering refugia.

There was modest variation in regards to habitat selection and Tb. Snakes achieved a mean Tb on alluvial slopes (29.4° C), followed by arroyos (29.2° C), rocky slopes (28.7° C) and alluvial flats (28° C). However, the mean Ts were highest in the two least frequented habitats, arroyos

(34.4° C) and alluvial flats (31° C). Mean Ts were the lowest on rocky slopes (29.8° C), the most frequented habitat selected by snakes. Tb profiles of snakes did not reveal a specific trend in its distribution among microhabitats. More subterranean microhabitats such as in burrows had the lowest mean Tb (26.1° C), and the highest were recorded under litter (31.1° C), which was one the least frequented microhabitats. Nonetheless, the most frequented microhabitats, under shrubs

(28.9° C), had mean Ts and Tmicro of 32° C and 28.3° C, respectively. The structural components of microhabitats containing shrubs had the most favorable temperature variables (Ts and Tmicro) to which snakes achieved a mean Tb similar to those in the active season as a whole (under shrubs = 28.9°C, active season = 28.7° C).

Differences in body temperatures between all individual B. subocularis were statistically significant. The differences in Tb for the snakes were probably due to a number of factors.

Individuals inhabited distinctive areas of various sizes, and hence the different habitats and respective microhabitats snakes selected had distinctive thermal qualities. Different periods within the active seasons also produced Tb differences. For instance, individual 03 (female) had a

61 Tb of 17.7° C in October during the latter part of the active season, and was located under a shrub throughout daylight hours. Conversely, another female (ID 02) had the highest recorded Tb at

34.8° C while under a shrub during the day in August. Behaviors such as basking in diurnal settings were only observed once in the active season, in which, a female (ID 03), was detected with its lower third of her body visibly exposed on 28 August 2010; Tb for individual 03 at that moment (16:40 h) was 19° C. The location of that individual was on a north-facing cliff on Flat

Top Mountains (elev. 1374 m, Fig. 31). Therefore, variables such as elevation and slope direction probably affects thermoregulation of B. subocularis throughout the active season.

With respect to other North American colubrids, average Tb for snakes were in general higher than P. obsoletus (28.3°C, Blouin-Demers and Weatherhead, 2001b; 28° C, Blouin-Demers and

Weatherhead, 2001a; 25.7° C, Jacob and McDonald, 1975), P. gloydi (28.4° C, Wilson and

Brooks, 2006), P. guttatus (28° C, Roark and Dorcas, 2000), P. catenifer (25.9° C, Kapfer et al.,

2008; 28.2° C, Fitch, 1999), P. melanoleucus (28.6° C, Diller and Wallace, 1996), P. ruthveni

(27.7° C, Himes et al., 2006), Thamnophis sirtalis (27.8° C, Gibson and Falls, 1979), Nerodia sipedon (24° C, Brown and Weatherhead, 2000), Thamnophis cyrtopsis and Thamnophis marcianus in Arizona (27.5° C, Rosen, 1991), S. triapsis in Arizona (25° C, Radke and Malcom,

2008); but lower than C. constrictor (31.9° C, Hammerson, 1987), M flagellum (31.6° C,

Hammerson, 1989; 32.1° C, Secor, 1995), M. lateralis (32.7° C, Hammerson, 1979), and

Thamnophis elegans (30.1° C, Peterson, 1987). In comparison to different populations of Black

Rat Snakes (P. obsoletus), mean body temperatures of B. subocularis were higher than Texas populations of P. obsoletus (27.5° C, Weatherhead et al., 2012). The thermal range of Tb of P. obsoletus varies latitudinally, with the lowest mean Tb in Canadian populations, and the warmest in the southernmost periphery of their range (Weatherhead et al., 2012). As far as large colubrids

62 are concerned, the distribution of B. subocularis in southern latitudes of temperate North

America also reflects the warmer thermal range of Tb, as did those reported by Sawyer (1993) and Sawyer and Baccus (1996).

Compared to North American rattlesnakes of the genus Crotalus, the mean body temperatures of B. subocularis were higher than C. cerastes in California (27.3° C, Secor, 1995), C. horridus in New York (26.9° C, Brown et al., 1982), C. scutulatus in Arizona (26.5° C, Pough, 1966), but were lower than C. atrox (29.3° C), C. molossus (29.6° C), and C. tigris (29.5° C) within the

Sonoran Desert in Arizona (Beck, 1995), and C. lepidus (29.3° C) in Texas (Beaupre, 1995).

Within IMRS, the mean Tb of C. lepidus was 29° C (Mata-Silva, 2011) during the active seasons, slightly higher than Trans-Pecos Rat Snakes. The thermal range of Tb of B. subocularis seems to be on par, or slightly lower, than rattlesnakes in the southern latitudes of North America.

Pantherophis obsoletus in Texas switch to nocturnal activity during the active season, while

Illinois and Canadian populations are strictly diurnal (Weatherhead et al., 2012). Regulation in activity patterns may respond positively to climate change in P. obsoletus throughout its range

(Weatherhead et al., 2012). The thermal range of Tb in B. subocularis during the active season is warmer than many temperate North American colubrids, although climate change in the

Chihuahuan Desert may potentially have adverse effects to those delicate habitats (Hoyt, 2002;

Nowak et al., 2002), and thus for thermoregulation of inclusive snakes like B. subocularis.

Radiotelemetry and Thermoregulation: Winter Period. - Trans-Pecos Rat Snakes on IMRS overwintered approximately six months out of the year. This inactive period lasts slightly longer than for Crotalus lepidus on IMRS (Mata-Silva, 2011). The mean number of days that B.

63 subocularis overwintered was 172.5 days. Information for one male (ID 04) was not accounted for, due to the unexpected failure in the individual’s transmitter signal.

Results showed Trans-Pecos Rat Snakes achieving a mean Tb of 15.3° C during the winter periods. No winter body temperatures were recorded in Sawyer’s (1993) study, so the information presented herein reflects the only known information regarding the wintering factors related to B. subocularis. The difference of body temperatures between the sexes was significant, as females average Tb were cooler (15° C) than for males (15.8° C). The range of body temperatures can be partially explained by the location of overwintering sites. One male (ID 04) overwintered high in a canyon (elev. 1345 m) about 1.5 km from its normal activity range, but had a mean Tb higher than all other snakes (18.1° C). In contrast, a female (ID 03) attained the lowest average Tb of all snakes (2.3° C) on 22 January 2011 and was located on a ridge near the top of Flat Top Mountain, at an elevation of 1358 m. The thermal critical minimum for Trans-

Pecos Rat Snakes is not known, although the low Tb attained by ID 03 suggests that the species is capable of tolerating low surrounding temperatures. That female maintained the same Tb from the late evening (approx. 22:30 h) to early morning (12:40 h), thereafter the Tb increased to 2.8°

C until 08:20 h. During the morning of 22 January 2011, the ambient temperature was 3.2° C, substrate temperature was 4° C, and the microhabitat temperature was 5.6° C; while the morning hours the next day saw temperatures of - 1.1°C, - 0.7° C, and 0° C (Ta, Ts, and Tmicro, respectively). The month of January is on average the coldest on IMRS (De la Cerda-Camargo,

2011), which was reflected by the lowest mean Tb of all B. subocularis. The warmer Tmicro were probably responsible for the snakes’ Tb from reaching freezing temperatures. The temperatures within winter refugia could have been influenced by Ts, as heat retained during daylight hours would have permitted the surrounding rocky microhabitats to absorb heat from solar radiation.

64 The snakes’ mean Tb were highest in November. One incident was observed with a female

(ID 03) basking outside its microhabitat (Fig. 32) after ingress. The snake was observed on 27

November 2010, and its body temperature was 13.5° C, with the lower third of its body exposed from within a crevice. Mean ambient temperatures on that day at that location were 12.5°, with

Ts 13.8° C and Tmicro at 14° C. This is the only incidence of B. subocularis basking during the winter season. Other colubrid snakes, such as P. obsoletus and P. guttatus, have been reported to bask in U. S. southern states during winter months (Ernst and Ernst, 2003).

The Chihuahuan Desert, however, has extended periods in which the environmental temperatures limit the surface activity of most snakes, as is the case with B. subocularis. The

Green Rat Snake (S. triaspis) from the boundary between the Chihuahuan Desert and Sonoran

Desert in Arizona possibly hibernates for short periods during winter months; captive snakes were encouraged to hibernate at a Tb of 15° C (Cranston, 1989). Senticolis triaspis is a close relative to B. subocularis (Pyron and Burbrink, 2009; Rodríguez-Robles and Jesús-Escobar,

1999), so their behavior may parallel each other to some degree, but that information needs to be investigated; little is known about the winter ecology of S. triaspis.

Daily variation by hour in Tb for B. subocularis during the winter period was generally stable

(approx. 15° C), from the 14:30 to 17:30 h time frame, and then a sudden rise after that.. A similar relationship was observed by Mata-Silva (2011) for C. lepidus occurring sympatrically on IMRS. Crotalus lepidus overwintered mostly on southeastern facing rocky slopes where ground temperatures were warmest, but B. subocularis selected northwestern (ID 02 and 04), western (ID 01 and 05), and northeastern facing slopes (ID 03). In the northern hemisphere, southern facing slopes of varying angles receive more solar radiation during the winter than

65 northern facing slopes (Sexton and Hunt, 1980; Hamilton and Nowak, 2009). In Mata-Silva’s

(2011) study, the next warmest slopes faced south followed by southwest. None of the overwintering sites of B. subocularis were found on southern facing slopes, so they seemed to prefer colder facing slopes. This explains why B. subocularis had relatively low average Tb during winter months in the study area.

In respect to Tb of B. subocularis with other colubrid snakes, B. subocularis Tb during the winter period fell within the range of M. flagellum (7 – 24° C) (Secor and Nagy, 1994), with one observation of 17° C (Cowles, 1941), and another with a mean Tb of 17.3° C (Secor, 1995).

Hibernating C. constrictor had average cloacal temperatures of 3.5 ° C in Michigan (Rosen,

1991), and 5° C in Utah (Parker and Brown, 1974), which was lower than B. subocularis. In T. sirtalis, Tb of hibernating snakes were much lower than B. subocularis, ranging between 2 – 7° C in British Columbia (MacArtney et al., 1989), and 3.4 – 7° C (Carpenter, 1953) in Michigan. A similar low Tb in T. elegans (cloacal temperature 5° C) was reported by Brown et al. (1974).

Compared to southwestern rattlesnakes, the mean Tb of B. subocularis was lower than C. lepidus

(19.2° C) occurring on IMRS (Mata-Silva, 2011) and C. atrox, C. molossus, and C. tigris (15.3 °

C) in Arizona (Beck, 1995). The differences in Tb are possibly due to a number of factors, such as the physical hibernacula characteristics (Sexton and Hunt, 1980), and the direction of slopes

(Sexton and Hunt, 1980; Hamilton and Nowak, 2009). Coluber constrictor moved within cave hibernacula in response to thermal clines during the winter period; snakes shifted from the entry of the hibernacula at initial phases of the winter, and moved deeper as the mid winter temperatures plummeted (Sexton and Hunt, 1980). It is unknown if B. subocularis displays a similar behavior, but the potential of B. subocularis basking during the winter months is feasible, but rarely observed on IMRS.

66 All monitored Trans-Pecos Rat Snakes overwintered singly at different sitess. Rock

Rattlesnakes (C. lepidus) occurring sympatrically on IMRS also displayed that behavior (Mata-

Silva, 2011). Snakes in general hibernate in large groups in more northern latitudes where they are inactive during most winter months (Gregory, 1982). Almost all rat snakes in northern temperate regions retreat into hibernation (Schulz, 1996) during the winter months, although this varies with geography and ecological conditions, especially in the lower latitudes. Most Rat snakes in North America hibernate in groups, which is in contrast to B. subocularis on IMRS.

The Western Fox Snake (P. vulpina) are known to congregate in human made structures in large numbers (166 individuals), as reported by Vogt (1981). Snakes also hibernate with other species of snakes, such has: P. emoryi and C. constrictor (Webb, 1970), M. flagellum and C. atrox, and

P. obsoletus with C. constrictor and P. melanoleucus (Gloyd, 1928). There are few records of colubrid snakes hibernating singly. The Pine snakes Pituophis ruthveni and P. melanoleucus hibernated singly in east Texas and Mississippi, respectively (Rudolph et al., 2007). In Utah, a large partitioned hibernaculum containing C. constrictor and T. elegans exhibited only a few individuals hibernating by themselves in separate crevices, otherwise groups of no more than six individuals congregted together at other sites (Brown et al., 1974). In North America, latitude

38° N was the hypothesized boundary for different winter denning behavior in rattlesnakes

(Sexton et al., 1992). Solitary overwintering has been observed below 38° C latitude in C. atrox,

C. molossus and C. tigris in Arizona (Beck, 1995), C. oreganus (Dugan et al., 2008), C. scutulatus (Cardwell, 2008), and a population of Massasaugas (Sistrurus catenatus) in southeastern Colorado (Wastell and Mackessy, 2011). Communal denning at higher elevations in southern latitudes were observed in rattlesnakes (Hamilton and Nowak, 2009), although individuals of the same species in lower elevations may overwinter singly. How this relates to

67 North American colubrid snakes, and subsequently B. subocularis, is not known, although the evidence so far indicates that winter temperatures are a factor, because sites at higher latitudes and elevations are normally lower than the reversed conditions. Additonally, the complexity and extensiveness of the overwintering sites could also be a factor (Burger et al., 1988), as the mountainous Chihuahuan Desert landscapes on IMRS contain many potential sites in addition to higher winter temperatures than in higher latitudes or at higher elevations. It is also possible that rattlesnake have different ecological requirements than colubrid snakes.

Finally, overwintering sites have been associated with population genetics related to gene flow dynamics in local populations of P. obsoletus (Blouin-Demers and Weatherhead, 2002).

They found that more distantly related individuals increased their movements further from hibernacula during the active seasons. The reasons for that are unknown, but the idea could be investigated with radiotelemetry on IMRS for populations of B. subocularis with individuals whose home ranges are in close proximity or overlapping.

Conservation Implications. - The study presented herein is the first comprehensive ecological study of the Trans-Pecos Rat Snake, Bogertophis subocularis, using radiotelemetry. Although the sample size was low, the information gathered during a span of two summers and two winters recorded a considerable amount on the biology of this species in the wild, especially details related to movement patterns, habitat/microhabitat selection, and thermoregulation behaviors during both the active and overwintering periods. Currently, B. subocularis is listed as

“least concern” by the IUCN (International Union for Conservation of Nature) Red List of

Threatened Species ™ (Hammerson and Santos-Barrera, 2007). However, certain populations may be declining in localized areas adjacent to roads due to collecting for the pet trade

68 (Hammerson and Santos-Barrera, 2007; Price, 1990; Fitzgerald et al., 2004) and in large metropolitan centers in the Chihuahuan Desert region, especially in the El Paso/Ciudad Juárez region, due to habitat destruction from urban sprawl. The species is protected in Big Bend

National Park, in a few state parks in Texas and New Mexico, on IMRS, and in at least two protected areas in Mexico (Hammerson and Santos-Barrera, 2007). The study presented herein can aid conservation biologists and environmentalists in determining which habitats and microhabitats to target during evaluation and implementing conservation practices for this species throughout is geographic range. Conserving this species and its habitats is paramount to protecting remaining non-disturbed areas harboring Chihuahuan Desert landscapes. Bogertophis subocularis is one of only a few representative of the “Rat Snake” group that occurs within the

Chihuahuan Desert, and is the only one that is more or less restricted to that desert’s geographic area. Because it is a relatively large and common snake where it resides, B. subocularis has high potential to be used as a model terrestrial vertebrate in ecological studies and those directed at conserving and preserving the Chihuahuan Desert biome.

69 LITERATURE CITED

ANGILLETTA JR., M. J., P. H. NIEWIAROWSKI, AND C. A. NAVAS. 2002. The evolution of thermal

physiology in ectotherms. Journal of Thermal Biology 27: 249-268.

AVERY, R. A. 1982. Field studies of body temperatures and thermoregulation. Pp. 93-166, In C.

Gans, and F. H. Pough (eds.), Biology of the Reptilia. Academic Press, New York, New York.

BEAUPRE, J.S. 1995. Comparative ecology of the mottled rock rattlesnake, Crotalus lepidus, in Big

Bend National Park. Herpetologica 51: 45-56.

BECK. D. D. 1995. Ecology and energetics of three sympatric rattlesnake species in the Sonoran

Desert. Journal of Herpetology 29: 211-223.

____. 2009. Biology of Gila Monsters and Beaded Lizards. University of California Press.

Berkeley and Los Angeles, California.

BEYER, H. L. 2004. Hawth’s Analysis Tools for ArcGIS. Available from:

BLOUIN-DEMERS, G. 2001. Thermoregulation and Habitat Use by Black Rat Snakes (Elaphe

obsoleta obsoleta) at the Northern Extreme of Their Distribution. Ph. D. Dissertation. Carleton

University. Ottawa, Ontario.

____, K. A. PRIOR, AND P. J. WEATHERHEAD. 2002. Comparative demography of black rat snakes

(Elaphe obsoleta) in Ontario and Maryland. J. of Zoology. 256: 1-10.

70 ____, AND P. J. WEATHERHEAD. 2001a. Thermal ecology of black rat snakes (Elaphe obsoleta) in a

thermally challenging environment. Ecology 82: 3025-3043

____, AND WEATHERHEAD, P.J., 2001b. Habitat-specific behavioral thermoregulation by black rat

snakes (Elaphe obsoleta obsoleta). Oikos 97: 59-68.

____, AND WEATHERHEAD, P.J., 2002. Implications of movement patterns for gene flow in Black

Rat Snakes (Elaphe obsoleta). Canadian Journal of Zoology 80: 1162-1172.

____, BJORGAN, L. P., AND P. J. WEATHERHEAD. 2007. Changes in the habitat use and movement

patters with body size in black ratsnakes (Elaphe obsoleta). Herpetologica 63: 421-429.

BONNET, X., R. SHINE, AND O. LOURDAIS. 2002. Taxonomic chauvinism. Trends in Ecology and

Evolution 17: 1-3.

BOUSKILA, A. 1995. Interactions between predation risk and competition: a field study of kangaroo

rats and snakes. Ecology 76: 165-178.

BOYLE, W. A. 2008. Can variation in risk of nest predation explain altitudinal migration of tropical

birds? Oecologia 155: 397-403.

BREWER, H. E. 2004. Habitat Diversity and Seasonal Changes in Small Mammall Populations at

Indio Mountains Research Station, Hudspeth County, Texas. M. S. Thesis. The University of

Texas at El Paso.

BROWN, A. E. 1901. A new species of Coluber from Western Texas. Proceedings of the Academy

of Natural Sciences of Philadelphia 53: 492-495.

71 BROWN, G. P., AND P. J. WEATHERHEAD. 2000. Thermal ecology and sexual dimorphism in

Northern Water Snakes, Nerodia sipedon. Ecological Monographs 70: 311–330.

BROWN, W. S., AND W. S. PARKER. 1976. Movement ecology of Coluber contrictor near

communal hibernacula. Copeia 1976: 225-242.

____, D. W. PYLE, K. R. GREENE, AND J. B. FRIEDLAENDER. 1982. Movement and temperature

relationships of Timber Rattlesnakes (Crotalus horridus) in northeastern New York. Journal of

Herpetology 16: 151-161.

____, W. S. PARKER, AND J. A. ELDER. 1974. Thermal and spatial relationships between two

species of colubrid snakes during hibernation. Herpetologica. 30: 32-38.

BURBRINK, F. T., AND R. A. PYRON. 2009. How does ecological opportunity influence rates of

speciation, extinction, and morphological diversification in New World Ratsnakes (Tribe

Lampropeltini)? Evolution. 64: 934-943

____, AND R. LAWSON. 2007. How and when did Old World Ratsnakes disperse into the New

World? Molecular Phylogenetics and Evolution 43: 173-189.

BURGER, J., R. T. ZAPPALORTI, M. GOCHFELD, W. I. BOARMAN, M. CAFFREY, V. DOIG, S. D.

GARBER, B. LAURO, M. MIKOVSKY, C. SAFINA, AND J. SALIVA. 1988. Hibernacula and summer

den sites of Pine Snakes (Pituophis melanoleucus) in the New Jersey pine barrens. Journal of

Herpetology 22: 425 – 433.

CAMPBELL, S. R., S. P. MACKESSY, AND J. A. CLARKE. 2008. Microhabitat use by brown treesnakes

(Boiga irregularis): effects of moonlight and prey. Journal of Herpetology 42:246-250.

72 CARCIUMARU, D., AND R. ORTEGA, 2008. Geologic structure of the northern margin of the

Chihuahua trough: Evidence for controlled deformation during Laramide Orogeny. Buletín de la

Sóciedad Mexicana 60: 43- 69.

CARDWELL, M. D. 2008. The reproductive ecology of Mohave rattlesnakes. Journal of Zoology

274: 65 – 76.

CARFAGNO, G. L. F., AND P. J. WEATHERHEAD. 2008. Energetics and space use: intraspecific and

interspecific comparisons of movements and home ranges of two Colubrid snakes. Journal of

Animal Ecology 77: 416-424.

CARPENTER, C. C. 1953. A study of hibernacula and hibernating associations of snakes and

amphibians in Michigan. Ecology 34: 74–80.

CLARKE, J. A., J. T. CHOPKO, AND S. P. MACKESSY. 1996. The effect on moonlight on activity

patterns of adult and juvenile Prairie Rattlesnakes (Crotalus viridis viridis). Journal of

Herpetology 30: 192-197.

COLLINS, J. T., AND T. W. TAGGERT. 2008. An alternative classification of the New World Rat

snakes (genus Pantherophis) [Reptilia: Squamata: Colubridae]). Journal of Kansas Herpetology

26: 16-18.

CONANT, R., AND J. T. COLLINS. 1998. Peterson Field Guide Series: A Field Guide to Reptiles and

Amphibians: Eastern and Central North America, 3rd ed. Houghton Mifflin Co., New York, New

York.

73 COOKE, S. J., S. G. HINCH, M. WIKELSKI, R. D. ANDREWS, L. J. KUCHEL, T. G. WOLCOTT, AND P. J.

BUTLER. 2004. Biotelemetry: a mechanistic approach to ecology. Trends in Ecology and

Evolution 19: 334-343.

CRANSTON, T. 1989. Natural history and captive husbandry of the western Green Rat Snake.

Vivarium 2: 8-11.

DALY, M., M. WILSON, P. R. BEHRENDS, M. I. WILSON, AND L. F. JACOBS. 1990. Characteristics of

Kangaroo Rats, Dipodomys merriami, associated with differential predation risk. Animal

Behavior 40: 380-389.

DEGENHARDT, W. G., AND P. B. DEGENHARDT. 1965. The host-parasite relationship between

Elaphe subocularis (Reptilia: Colubridae) and Aponomma elaphensis (Acarina: Ixodidae).

Southwestern Naturalist 10: 167-178.

st ____, C. W. PAINTER, AND A. H. PRICE. 1996. Amphibians and Reptiles of New Mexico. 1 ed.

The University of New Mexico Press, Albuquerque, New Mexico.

DE LA CERDA-CAMARGO, F. 2011. Influence of Orography on the Weather Patterns and Water

Availability of a Topographically Complex Chihuahuan Desert Region. M.S. thesis, The

University of Texas at El Paso.

DE QUEIROZ, K. 2005. A unified concept of species and its consequences for the future of

taxonomy. Proceedings of the California Academy of Sciences 56: 196 - 215.

DILLER, L. V., AND R. L. WALLACE. 1996. Comparative ecology of two snake species (Crotalus

viridis and Pituophis melanoleucus) in southwestern Idaho. Herpetologica 52: 343 -360.

74 DICKMAN, C. R. 1992. Predation and habitat shift in the house mouse, Mus domesticus. Ecology

73: 313-322.

DIXON, J. R., AND J. E. WERLER. 2000. Texas Snakes: A Field Guide. The University of Texas

Press. Austin, TX.

DODD, C. K. JR. 1993. Strategies for snake conservation. In R. A. Seigel and J. T. Collins (eds.).

Snakes: Ecology and Behavior, pp. 363 -393. McGraw-Hill, New York.

____, AND W. J . BARICHIVICH. 2007. Movements of large snakes (Drymarchon, Masticophis) in

North-Central Florida. Florida Scientist 70: 83-94.

DOWNS, J. A. AND M. W. HORNER. 2007. Network-based kernel density based estimation for home

range analysis. Proceedings of the Ninth International Conference on Geocomputation,

Maynooth, Ireland.

DUGAN, E. A., A. FIGUEROA, AND W. K. HAYES. 2008. Home range size, movements, and mating

phenology of sympatric Red Diamond (Crotalus ruber) and Southern Pacific (C. oreganus

helleri) Rattlesnakes in southern California. In W. K. Hayes, K. R. Beaman, M. D. Cardwell, and

S. P. Bush (eds.), The Biology of Rattlesnakes, pp. 353 - 364. Loma Linda University Press,

Loma Linda, California.

DURNER, G. M., AND J. E.GATES. 1993. Spatial ecology of black rat snakes on Remington Farms,

Maryland. Journal of Wildlife Management 57: 812-826.

DUVALL, D., M. B. KING, AND K. J. GUTZWILLER. 1985. Behavioral ecology and ethology of the

Prairie Rattlesnake. National Geographic Research 1:80-111.

75 DUVAL, E. H., H. W. GREENE, AND K. L. MANNO. 2006. Laughing Falcoln (Herpetotheres

cachinnas) predation on Coral Snakes (Micrurus nigrocinctus). Biotropica 38: 566-568.

ERNST, C. H., AND E. M. ERNST. 2003. Snakes of the United States and Canada. Smithsonian

Books. Washington, D.C.

ESCAMILLA, R. A. 2012. An Assessment of Land Cover Change at the Indio Mountains Research

Station. Ph. D. Dissertation. The University of Texas at El Paso.

ESRI. 2004. ArcGIS 9.3 ESRI Software. TASC, Inc. Redlands, California.

FITCH. H. S. 1963. Natural History of the Black Rat Snake (Elaphe o. obsoleta) in Kansas. Copeia

1963: 649-658.

____. 1999. A Kansas Snake Community: Composition and Changes Over 50 Years. Krieger

Publishing Co., Malabar, Florida.

FITZGERALD, L. A., C. W. PAINTER, A. REUTER, AND C. HOOVER. 2004. Collection, trade, and

regulation of reptiles and amphibians of the Chihuahuan Desert ecoregion. TRAFFIC North

America. World Wildlife Fund, Washington D.C.

GASTON, K. J., T. M. BLACKBURN, AND K. K. GOLDEWIJK. 2003. Habitat conversion and global

avian biodiversity loss. Proceedings of Royal Society London B 270: 1293-1300.

GERALD, G. W., M. A. BAILEY, AND J. M. HOLMES. 2006. Movements and activities of Northern

Pine Snakes (Pituophis melanoleucus melanoleucus) in Middle Tennessee. Journal of

Herpetology 40: 503-510.

76 GIBSON, A. R., AND J. B. FALLS. 1979. Thermal biology of the Common Garter Snake Thamnophis

sirtalis (L.). I. Temporal variation, environmental effects and sex differences. Oecologia 43: 79-

97.

GLOYD, H. K. 1928. The amphibians and reptiles and Franklin County, Kansas. Transactions of the

Kansas Academy of Sciences 31: 115-141.

GRANT, B. W., AND A. E. DUNHAM. 1988. Thermally imposed time constraints on the activity of

the desert lizard Sceloporus merriami. Ecology 69: 167-176.

GREGORY, P. T. 1982. Reptilian hibernation. In C. Gans and F. H. Pough (eds.). Biology of the

Reptilia, Vol. 13, pp. 53-154. Academic Press, New York, New York.

____, J. M. MACARTNEY, AND K. W. LARSEN. 1987. Activity patterns. In R.A. Seigel, J. T. Collins

and S. S. Novak (eds.), Snakes: Ecology and Evolutionary Biology. pp. 422–477. McGraw-Hill,

New York.

GREENBERG, D. B., AND W. J. MCCLINTOCK. 2008. Remember the third dimension: Terrain

modeling improves estimates of snake home range size. Copeia 2008: 801-806.

GREENE, H. W. 1997. Snakes. The Evolution of Mystery in Nature. The University of California

Press. Berkeley and Los Angeles, California.

GRISMER, L. L. 2002. Amphibians and Reptiles of Baja California, Including Its Pacific Islands

and the Islands in the Sea of Cortés. The University of California Press. Berkeley and Los

Angeles, California.

77 HAMILTON, B. T., AND E. M. NOWAK. 2009. Relationships between insolation and rattlesnake

hibernacula. Western North American Naturalist 69: 319-328.

HAMMERSON, G. A. 1987. Thermal behaviour of the snake Coluber constrictor in west-central

California. Journal of Thermal Biology 12: 195-197.

____. 1989. Effects of weather and feeding on body temperature and activity in the snake

Masticophis flagellum. Journal of Thermal Biology 14: 219-224.

____, AND G. SANTOS-BARRERA. 2007. Bogertophis subocularis. In: IUCN 2012. IUCN Red List

of Threatened Species. Version 2012.1. . Downloaded on 12 July 2012.

HARDY, D. L., AND H. W. GREENE. 1999. Surgery on rattlesnakes in the field for implantation of

transmitters. Sonoran Herpetologist 12: 25-27.

HIMES, J. G., L. M. HARDY, D. C. RUDOLPH, AND S. J. BURGDORF. 2006. Movement patterns and

habitat selection by native and repatriated Louisiana pine snakes (Pituophis ruthveni):

implications for conservation. Herpetological Natural History 9: 103-116.

HOSS, S. K., C. GUYER, L. L. SMITH, AND G. W. SHUETT. 2010. Multiscale influences of landscape

composition and configuration on the spatial ecology of Eastern Diamond-backed Rattlesnakes

(Crotalus adamanteus). Journal of Herpetology 44: 110-123.

HOYT, C. A. 2002. The Chihuahuan Desert: diversity at risk. Endangered Species Bulletin XXVII:

16-17.

HUEY, R. B., AND J. G. KINGSOLVER. 1989. Evolution of thermal sensitivity of ectotherm

performance. Trends in Ecology and Evolution 4: 131-135.

78 HYSLOP, N. L. 2001. Movements, Habitat Use, and Survival of the Threatened Eastern Indigo

Snake (Drymarchon couperi) in Georgia. M.S. Thesis. Purdue University.

ISBELL, L. A. 2006. Snakes as agents of evolutionary change in primate brains. Journal of Human

Evolution 51: 1-35.

JACKSON, J. A. 1976. Relative climbing tendencies of Gray (Elaphe obsoleta spiloides) and Black

Rat Snakes (Elaphe o. obsoleta). Herpetologica 32: 359-361.

JACOB, J. S., AND H. S. MCDONALD. 1975. Temperature preferences and electrocardiography of

Elaphe obsoleta (Serpentes). Comparative Biochemical and Physiology Part A. Physiology 52:

591-594.

JANZEN, D. H. 1976. The depression of reptile biomass by large herbivores. The American

Naturalist 110: 371-400.

JENNRICH, R. I. AND F. B. TAYLOR. 1969. Measurement of non-circular home range. Journal of

Theoretical Biology 22: 227-237.

JOHNSON, J. D. 2000. Indio Mountains Research Station - A Place of Learning in the Desert.

Chihuahuan Desert Discovery 45: 4-5, 11.

____, V. MATA-SILVA, AND A. RAMIREZ-BAUTISTA. 2010. Geographic distribution and

conservation of the herpetofauna of southeastern Mexico. In L. D. Wilson, J. H. Towsend, and J.

D. Johnson (eds.), Conservation of the Mesoamerican Amphibians and Reptiles, pp. 323-396.

Eagle Mountain Publishing, L.C., Eagle Mountain, Utah.

79 JOHNSON, R. W., R. R. FLEET, AND D. C. RUDOLPH. 2007. Spatial Ecology of the Coachwhip,

Masticophis flagellum (Squamata: Colubridae), in Eastern Texas. Southeastern Naturalist 6: 111-

124.

KAPFER, J. M., J. R. COGGINS, AND R. HAY. 2008. Spatial ecology and habitat selection of

Bullsnakes (Pituophis catenifer sayi) at the northern periphery of their geographic range. Copeia

2008: 815- 826.

____, C. W. PEKAR, D. M. REINEKE, J. R. COGGINS, AND R. HAY. 2010. Modeling the relationship

between habitat preferences and home-range size: a case study on a large mobile colubrid snake

from North America. Journal of Zoology 282: 13-20.

KEOGH, J. S., AND F. P. DESERTO. 1994. Temperature dependent behavior in three species of North

American colubrids. Journal of Herpetology 28: 258-261.

____. 1996. Evolution of the colubrid snake tribe Lampropeltini: a morphological perspective.

Herpetologica 52: 406- 416.

KOTLER, B. P., J. S. BROWN, R. H. SLOWTOW, W. L. GOODFRIEND, AND M. STRAUSS. 1993. The

influence of snakes on the foraging behavior of gerbils. Oikos 67: 309 – 316.

LEGENDRE, P., AND M. J. FORTIN. 1989. Spatial pattern and ecological analysis. Plant Ecology 80:

107-138.

LEVINS, R. 1968. Evolution in Changing Environments. Princeton University Press. Princeton,

New Jersey.

80 LILLYWHITE, H.B. 1987. Temperature, energetics, and physiological ecology. In R.A. Seigel, J. T.

Collins and S. S. Novak (eds.), Snakes: Ecology and Evolutionary Biology, pp. 422-477.

McGraw-Hill, New York.

MACARTNEY, J. M., P.T. GREGORY, AND K. W. LARSEN. 1988. Tabular survey of data on

movements and home ranges of snakes. Journal of Herpetology 22: 61-73.

____, J. M. LARSON, AND P. T. GREGORY. 1989. Body temperatures and movements of hibernating

snakes (Crotalus and Thamnophis) and thermal gradients of natural hibernacula. Canadian

Journal of Zoology 67: 108-114.

MAKARENKOV, V., AND LEGENDRE, P. 2002. Nonlinear redundancy analysis and canonical

correspondence analysis based on polynomial regression. Ecology 83:1146-1161.

MALONE, J. H. 2001. Bogertophis subocularis (Trans-Pecos Rat Snake). Geographic distribution.

Herpetological Review. 32: 122.

MATA-SILVA, V. 2011. Ecology of the Rock Rattlesnake, Crotalus lepidus, in the Northern

Chihuahuan Desert. Ph. D. Dissertation. The University of Texas at El Paso.

____, S. DILKS, AND J. D. JOHNSON. 2010. Crotalus lepidus (Rock Rattlesnake). Diet.

Herpetological Review 41:235-236.

____, J. D. JOHNSON, AND A. ROCHA. 2011. Crotalus lepidus (Rock Rattlesnake). Feeding

behavior. Herpetological Review 42:439.

MOON, B. R., AND A. M. RABATSKY. 2004. Bogertophis subocularis (Trans-Pecos Rat Snake).

Prey. Herpetological Review 35: 175.

81 MORAFKA, D. J. 1977. A Biogeographic Analysis of the Chihuahuan Desert Through its

Herpetofauna. Dr. W. Junk B.V., The Hague, The Netherlands.

MORENO-RUEDA, G., AND M. PIZARRO. 2007. The relative influence of climate, environmental

heterogeneity, and human population on the distribution of vertebrate species richness in south-

eastern Spain. Acta Oecologica 32: 50-58.

MILLER, GABRIEL, J. 2008. Home Range Size, Habitat Associations and Refuge Use of the Florida

Pine Snake, Pituophis melanoleucus mugitus, in Southwest Georgia, U.S.A. M.S. Thesis. The

University of Florida. Gainesville, Florida.

NOWAK, E. M., T. HARE, AND J. MCNALLY. 2002. Management of “nuisance” vipers: effects of

translocation on Western Diamond-backed Rattlesnakes (Crotalus atrox). In G. W. Schuett, M.

Höggren, M. E. Douglas, and H. W. Greene (eds.), Biology of the Vipers, pp. 533-560. Eagle

Mountain Publishing, Eagle Mountain, Utah.

PARKER, W. S., AND W. S. BROWN. 1980. Comparative ecology of two colubrid snakes,

Masticophis t. taeniatus and Pituophis melanoleucus deserticola, in northern Utah. Milwaukee

Public Mus. Publications in Biology and Geology 7: 1-104.

____, AND M. V. PLUMMER. 1987. Population ecology. In R.A. Seigel, J. T. Collins and S. S.

Novak (eds.), Snakes: Ecology and Evolutionary Biology. pp. 422-477. McGraw-Hill, New

York.

PAULY, G. B., AND T. LADUC. 2009. Bogertophis subocularis. (Trans-Pecos Rat Snake)

Arboreality. Herpetological Review 40: 93.

82 PETERSON, C. R. 1987. Daily variation in the body temperatures of free-ranging Garter Snakes.

Ecology 68: 160-169.

PLUMMER, M. V., AND J. D. CONGDON. 1994. Radiotelemetric study of activity and movements of

Racers (Coluber constrictor) associated with a Caroline bay in South Carolina. Copeia 1994: 20-

26.

____.1996. Rates of metabolism and water flux in free-ranging Racers, Coluber constrictor.

Copeia 1996: 8-14.

PORTER W. P., S. BUDARAJU, W. E. STEWART, AND N. RAMANKUTTY. 2000. Calculating climate

effects on birds and mammals: impacts on biodiversity, conservation, population parameters, and

global community structure. American Zoologist 40: 597-630.

POUGH, F. H. 1966. Ecological relationships in southeastern Arizona with notes on other species.

Copeia 1966: 676- 683.

____, R. M. ANDREWS, J. E. CADLE, M. L. CRUMP, A. H. SAVITZKY AND K. D. WELLS. 2004.

Herpetology. 3rd edition. Pearson Preston Hall. Upper Saddle River, New Jersey.

PRICE, R. M. 1990. Bogertophis. Catalogue of American Amphibians and Reptiles 497: 1-2.

PYRON, R. A. AND F. T. BURBRINK. 2009. Neogene diversification and taxonomic stability in the

snake tribe Lampropeltini (Serpentes: Colubridae). Molecular Phylogenetics and Evolution 52:

524-529.

RADKE, W. R. AND J. W. MALCOM. 2008. Notes on the ecology of Green Ratsnakes (Senticolis

triapsis) in southeastern Arizona. Herpetological Conservation and Biology 4: 9-13.

83 REINERT, H. K. 1984. Habitat separation between sympatric snake populations. Ecology 65: 478-

486.

____. 1992. Radiotelemetric field studies of pitvipers: Data acquisition and analysis., In Campbell

J. M., and E. D. Brodie (eds.) The Biology of the Pitvipers. pp. 185-197. Selva Press, Tyler,

Texas.

RHOADS, D. 2008. The Complete Suboc: A Comprehensive Guide to the Natural History, Care,

and Breeding of the Trans-Pecos Ratsnake. Lansing: ECO Herpetological Publishing &

Distribution, Lansing, Michigan.

ROARK, A. W., AND M. E. DORCAS. 2000. Regional body temperature variation in Corn Snakes

measured using temperature-senstative passive integrative transponders. Journal of Herpetology

34: 481-485.

ROBINSON, W. D., G. ROMPRE AND T. R. ROBINSON. 2005. Videography of Panama bird nests

show snakes are principal predators. Ornithologia Neotropical 16: 187-195.

RODRÍGUEZ-ROBLES, J. A., AND J. M. DE JESÚS-ESCOBAR. 1999. Molecular systematics of New

World lampropeltinine snakes (Colubridae): implications for biogeography and evolution of food

habitats. Biological Journal of Linnean Society 68:355-385.

ROSEN, P. C. 1991. Comparative field study of thermal preferenda in Garter Snakes (Thamnophis).

Journal of Herpetology 25: 301- 312.

ROW, J. R., AND G. BLOUIN-DEMERS. 2006. Kernels are not accurate estimators of home-range size

for herpetofauna. Copeia 2006: 797 -802.

84 RUDOLPH, V. C., R. R. SCHAEFER, S. J. BURGDORF, M. DURAN, AND R. N. CONNER. 2007. Pine

Snake (Pituophis ruthveni and Pituophis melanoleucus lodingi) hibernacula. Journal of

Herpetology 41: 560-565.

SAWYER, M. W. 1993. A Study Of The Trans-Pecos Rat Snake (Bogertophis Subocularis) To

Evaluate Movement, Home Range, Temperature, Den Site Preference, And Plant Association

Using Radio Telemetry. M. S. Thesis. Southwest Texas State University.

____, AND J .T., BACCUS. 1996. Movement ecology and thermal biology of Bogertophis

subocularis from Texas (Serpentes: Colubridae). Southwestern Naturalist 41: 182-186.

SCHULZ, K. D. 1996. A Monograph of the Genus Snakes of the Genus Elaphe Fitzinger, Koeltz

Scientific Books, Havlicuv Brod.

SECOR, S. M. 1995. Ecological Aspects of Foraging Mode for the Snakes Crotalus cerastes and

Masticophis flagellum. Herpetological Monographs 9: 169-186.

____, AND K. A. NAGY. 1994. Bioenergetic correlates of foraging mode for the snakes Crotalus

cerastes and Masticophis flagellum. Ecology 75: 1600-1614.

SEEBACHER, F., AND C. E. FRANKLIN. 2005. Physiological mechanims of thermoregulaion in

reptiles: a review. Journal of Comparative Physiology 175: 533-541.

SEXTON, O. J., AND S. R. HUNT. 1980. Temperature relationships and movements of snakes

(Elaphe obsoleta, Coluber constrictor) in a cave hibernaculum. Herpetologica 36:20-26.

85 ____, P. JACOBSON, AND J. E. BRAMBLE. 1992. Geographic variation in some activities associated

with hibernation in Neartic pitvipers. In J. A. Campbell and E. D. Brodie, Jr. (eds.). Biology of

the Pitvipers, pp. 337-346. Selva, Tyler, Texas.

SHEWCHUK, C. H. 1996. The Natural History and Movement Patterns in the Gopher Snake

(Pituophis melanoleucus) in Southern British Columbia. M. S. Thesis. The University of

Victoria, British Columbia, Canada.

SPERRY, J. H., AND C. A. TAYLOR. 2008. Habitat use and seasonal activity patterns of the Great

Plains Ratsnake (Elaphe guttatus emoryi) in Central Texas. Southwestern Naturalist 53: 444-449.

TANNER, W. W. 1985. Snakes of Western Chihuahua. Western North American Naturalist 45: 615-

675.

TENNANT, A. 1984. The Snakes of Texas. Texas Montly Press. Austin, Texas.

rd _____. 2006. Lone Star Field Guide to Texas Snakes (3 ed.). Taylor Trade Publishing, Lanham,

Maryland.

TIEBOUT, H. M., AND J. R. CARY. 1987. Dynamic spatial ecology of the Water Snake, Nerodia

sipedon. Copeia 1987: 1-18.

VOGT, R. C. 1981. Natural History of Amphibians and Reptiles of Wisconsin. Milwaukee Public

Museum. Milwaukee, Wisconsin

WALDRON, J. L., S. H. BENNETT, S. M. WELCH, M. E. DORCAS, J. D. LANHAM, AND W.

KALINOWSKY. 2006. Habitat specificity and home-range size as attributes of species vulnerability

to extinction: a case study using sympatric rattlesnakes. Animal Conservation 9: 414- 420.

86 WALTON, C. J., MARTINEZ-GONZALEZ, F., AND R. D. WORTHINGTON. 2005. Desert vegetation and

timing of solar radiation. Journal of Arid Environments 60: 697-707.

WASTELL, A. R., AND S. P. MACKESSY. 2011. Spatial ecology and factors influencing movement

patterns of Desert Massasauga Rattlesnakes (Sistrurus catenatus edwardsii) in southeastern

Colorado. Copeia 2011: 29 -37.

WEATHERHEAD, P. J., AND BLOUIN-DEMERS. 2004. Understanding avian nest predation: why

ornithologists should studysnakes. Journal of Avian Biology 35: 185-190.

____, J. H. SPERRY, G. L. F. CARFAGNO, AND G. BLOUIN-DEMERS. 2012. Latitudinal variation in

thermal ecology of North American ratsnakes and its implications for the effect of climate

warming on snakes. Journal of Thermal Biology 37: 273-281.

WEAVER, R. E. 2011. Effects of simulated moonlight on activity on the Desert Nightsnake

(Hypsiglena chlorophaea). Northwest Science 85: 497-500.

WEBB, J. K., R. M. PRINGLE, AND R. SHINE. 2004. How do nocturnal snakes select diurnal retreat

sites? Copeia 2004: 919-925.

WEBB, R. G. 1970. Reptiles of Oklahoma. Norman: University of Oklahoma Press.

____. 1990. A description of a new subspecies of Bogertophis subocularis (Brown) from northern

Mexico (Serpentes: Colubridae). Texas Journal of Science 42: 227-243.

WELDON, P. J., F. M. DIVITA, AND G. A. MIDDENDORF III. 1987. Responsess to snake odors by

laboratory mice. Behavioral Processes 14: 137-146.

WILSON, E. O. 1992. The Diversity of Life. London. Harvard University Press.

87 WORTHINGTON, R. D. 1980. Elaphe subocularis. Catalogue of American Amphibians and Reptiles.

Society of the Study of Amphibians and Reptiles 268:1-2.

____, C. S. LIEB, AND W. ANDERSON. 2004. Biotic Resources of Indio Mountains Research

Station, Southern Hudspeth County, Texas. UTEP. Privately Printed. El Paso, Texas.

88 APPENDIX

APPENDIX 1. Home ranges of five radiotracked Bogertophis subocularis on IMRS.

APPENDIX 1-A. All home ranges and geographic locations of B. subocularis radiotracked on

IMRS.

APPENDIX 1-B. Geographic locations (open circles), MCP (continuous line) and 50% kernel area

(dotted lines) of female B.subocularis ID: 01, radiotracked on IMRS from July 2009 to August

2010.

APPENDIX. 1-C. Geographic locations (open circles), MCP (continuous line) and 50% kernel area

(dotted lines) of female B.subocularis ID: 02, radiotracked at IMRS from September 2009 to

October 2010.

APPENDIX. 1-D. Geographic locations (open circles), MCP (continuous line) and 50% kernel area

(dotted lines) of female B.subocularis ID: 03, radiotracked at IMRS from August 2010 to May

2011.

APPENDIX. 1-E. Geographic locations (open circles), MCP (continuous line) and 50% kernel area

(dotted lines) of male B.subocularis ID: 04, radiotracked at IMRS from July 2009 to August

2010.

APPENDIX. 1-F. Geographic locations (open circles), MCP (continuous line) and 50% kernel area (dotted lines) of male B.subocularis ID: 05, radiotracked at IMRS from August 2010 to July

2011.

94 VITA

Arturo Rocha Blanco was born on January 11, 1985, in El Paso Texas. He is the second of three children born to Alejandro and Norma Rocha. Arturo graduated from Jefferson High

School in El Paso, Texas in 2003. He attended the University of Texas at El Paso and obtained his Bachelor of Science Degree in Biological Sciences in 2008. Since 2009, he has worked as a

Masters Candidate under the direction of Dr. Jerry D. Johnson, in the Department of Biological

Sciences at the University of Texas at El Paso. During this time, Arturo has worked as a

Graduate Teaching Assistant during his graduate studies. His research interests are those in tetrapod zoology and ecology (with a particular interest in herpetology) and conservation.

Arturo is a member of the Society for the Advancement of Chicanos and Native Americans in

Science, and has presented his work at the Southwestern Association of Naturalists meetings, as well as attended the Ecological Society of America meetings.

Permanent Address: 369 S. Glenwood St., El Paso, TX 79905

This thesis was typed by Arturo Rocha.