Phrynosoma Blainvillii) in the Southern San Joaquin Valley of California

ECOLOGY AND DEMOGRAPHY OF THE BLAINVILLE'S HORNED LIZARD (PHRYNOSOMA BLAINVILLII) IN THE SOUTHERN SAN JOAQUIN VALLEY OF CALIFORNIA

SUSAN MARIE HULT

A Thesis submitted to the Department of Biology California State University, Bakersfield In Partial Fulfillment of the Degree of Masters of Science

JUNE 2014

iii

SUSAN MARIE HULT

2014

ECOLOGY AND DEMOGRAPHY OF THE BLAINVILLE'S HORNED LIZARD (PHRYNOSOMA BLAINVILLII) IN THE SOUTHERN SAN JOAQUIN VALLEY OF CALIFORNIA

Susan M. Hult

This thesis has been accepted on behalf of the Department of Biology by their supervisory committee:

Dr. David J. Germano Committee Chair

Dr. Steve Laymon

Dr. Brandon Pratt

ACKNOWLEDGEMENTS

I would sincerely like to thank my advisor, Dr. David Germano, for his patience

throughout the entire processes of coursework, research, fieldwork, and writing that resulted in

the completion of my degree. His professional support in the realms of writing, statistical

analysis, and editing has been invaluable. I also truly appreciate Dr. Stephen Laymon, who has

proven to be an incredible source of moral, professional, and field support at Atwell and in the

capacity of serving on my committee. I likewise thank Dr. Brandon Pratt for his ideas, friendly support, and review of my manuscript, which added greatly to the integrity of this thesis and for serving on my committee.

Without the Bureau of Land Management's (BLM) Student Career Experience Program, I

most likely would not have been able to carry out this research and obtain my degree. I hope

(and believe) this research serves as a valuable source of information in which they can use to

make land management decisions beneficial for P. blainvillii conservation in the southern San

Joaquin Valley. I am extremely grateful for the strong support of my colleagues and supervisors

at the BLM: John Skibinski, Steve Larson, Peter DeWitt, Denis Kearns, Amy Kuritsubo,

Joaquin Martinez, and Larry Saslaw. They provided invaluable technical and field expertise as well as assisted in tracking and data gathering, of which I particularly appreciated during the nocturnal hours! I had excellent assistance from Dana Gasper, Teresa O'Keefe, and Natalie

Montague who were willing to give large amounts of their time to gather telemetry, demographic, morphologic, and habitat data for this study. Without their assistance, the data would not be as robust as it is.

Finally, the support of friends and family members truly kept me afloat whether they were

nearby or 3,000 miles away at home in Minnesota. The support of loved ones was just as, if not

v more so, crucial to the journey as professional support was, even if some of them had no idea what a "horny toad" is!

ECOLOGY AND DEMOGRAPHY OF THE BLAINVILLE'S HORNED LIZARD (PHRYNOSOMA BLAINVILLII) IN THE SOUTHERN SAN JOAQUIN VALLEY OF CALIFORNIA Susan M. Hult

Department of Biology, California State University, Bakersfield

ABSTRACT

The Blainville's Horned Lizard (Phrynosoma blainvillii) is endemic to California and ranges from northern California (Butte County), to the northwestern tip of Baja California in the southern part of its range, west of the Sierra Nevada Mountains and the southern California deserts in the eastern part of its range, and along the Pacific coast from northern Baja California to Monterey, California in the western part of its range. Phrynosoma blainvillii is listed as a California Species of Special Concern and a Bureau of Land Management (BLM) Sensitive Species. Human activities have been primarily responsible for declines in populations. There has been few field research studies published on the general ecology of P. blainvillii, particularly in the San Joaquin Valley. I initiated a radio-telemetry study to collect data on home range size and habitat use at two sites (Atwell Island and Semitropic Ridge Preserve) in the southern San Joaquin Valley, California. I calculated home range size from 10 lizards, five at each site. Using the 100% Minimum Convex Polygon (MCP) estimator I found home range sizes were between 0.58 ha to 13.93 ha, with an average size of 4.98 ha (± 1.54). When above ground and active, P. blainvillii at either site used areas of bare ground more often than expected based on equal use. At the Semitropic site, the lizards used areas under shrubs almost as often as bare ground, while at the Atwell site the lizards used areas of sparse vegetation more often than expected, but not as much as bare ground. Lizards at both sites used medium-dense and dense areas of vegetation much less than expected based on equal use. In adult P. blainvillii, we recorded a moderately skewed sex ratio of more males than females, but in young P. blainvillii, there were more females than males. Average snout-vent length (SVL) of females was 72.31 mm and for males 68.81 mm. The adult horned lizards were most active in April and May while young horned lizards were most active in August and September. In the spring, the morning activity hours peaked at 0900–1100, in summer, it was 0900–1000, and in fall, it was 0900–1300. All age classes of P. blainvillii were most often above ground and active at surface temperatures of 28– 34°C. The presence of alkali flats and sandy soil correlated with a high abundance of horned lizards, and within our two study locations, they revealed a distinct preference for Sandridge loamy fine sand over other available soil types. The lizards used kangaroo rat burrows rather than shrubs for heat refugia but used shrubs frequently as an escape from predators. Food items found in scats were predominantly ants, but beetles and other arthropods were also found in large numbers.

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TABLE OF CONTENTS

CHAPTER 1. INTRODUCTION ...... 1 Literature Cited ...... 17 CHAPTER 2. HOME RANGE AND HABITAT USE OF THE BLAINVILLE’S HORNED LIZARD (PHRYNOSOMA BLAINVILLII) IN THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA ..... 23 Introduction ...... 24 Materials and Methods ...... 27 Study sites ...... 27 Field methods ...... 30 Data analysis ...... 33 Results ...... 36 Discussion ...... 38 Literature Cited ...... 45 CHAPTER 3. DEMOGRAPHICS, MORPHOLOGY, THERMOBIOLOGY, AND HABITAT PREFERENCE OF A POPULATION OF BLAINVILLE'S HORNED LIZARD IN THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA ...... 58 Introduction ...... 59 Materials and Methods ...... 62 Study sites ...... 62 Field data collection ...... 65 Demography and morphometrics ...... 66 Activity ...... 67 Habitat assessment ...... 68 Statistical analysis ...... 68 Results ...... 70 Demography and morphometrics ...... 70 Activity ...... 70 Habitat assessment ...... 71 Discussion ...... 72 Literature Cited ...... 79 CHAPTER 4. DIET ANALYSIS OF A POPULATION OF THE BLAINVILLE'S HORNED LIZARD (PHRYNOSOMA BLAINVILLII) FROM THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA, USA ...... 93 CHAPTER 5. CONCLUSIONS AND RECOMMENDATIONS FROM THE PRESENTED STUDIES OF BLAINVILLE'S HORNED LIZARD (PHRYNOSOMA BLAINVILLII) IN THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA ...... 98 Home Range ...... 98 Habitat Use ...... 100 Habitat Preference ...... 101 Activity Patterns ...... 102 Demographics And Morphology ...... 103 Literature Cited ...... 105

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LIST OF TABLES

Chapter 2. HOME RANGE AND HABITAT USE OF THE BLAINVILLE’S HORNED LIZARD (PHRYNOSOMA BLAINVILLII) IN THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA

Table 1. Radio-telemetry data for 14 Phrynosoma blainvillii at the Atwell Island and Semitropic Ridge Preserve sites in 2010 in the southern San Joaquin Valley, California...... 50

Table 2. Home range estimates of 10 Phrynosoma blainvillii based on 100% minimum convex polygon (MCP) and Fixed-K Local Convex Hull (LoCoH) at the 100% isopleth level at the Atwell Island and Semitropic Ridge Preserve sites in 2010 in the southern San Joaquin Valley, California...... 51

Chapter 3. DEMOGRAPHICS, MORPHOLOGY, THERMOBIOLOGY, AND HABITAT PREFERENCE OF A POPULATION OF BLAINVILLE'S HORNED LIZARD IN THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA

Table 1. Soil and habitat characteristics of Locations 1and 2 in the southern San Joaquin Valley in Kings and Tulare counties, California, USA...... 85

Table 2. Sex, age class, and descriptive statistics of snout-vent length (SVL) and body mass of Phrynosoma blainvillii captured April–November in 2009 and 2010 in the southern San Joaquin Valley in Tulare and Kings counties, California, USA...... 87

LIST OF FIGURES

Chapter 1. INTRODUCTION

Figure 1. Historic range of the Blainville’s Horned Lizard (Phrynosoma blainvillii), formerly the Coast Horned Lizard (P. coronatum), in California...... 2

Figure 2. Terminology for selected characteristics of the left lateral features of the head of Phrynosoma blainvillii...... 9

Figure 3. Dorsal view of an adult Phrynosoma blainvillii in the Southern San Joaquin Valley showing some of the identifying characteristics...... 10

Figure 4. Ventral views of Phrynosoma blainvillii from the southern end of the San Joaquin Valley, California showing variation in coloring and mottling. ……………………….…..11

Figure 5. Photograph of male and female P. blainvillii from the southern San Joaquin Valley, California …….……………………………………………...... …………………….…..12

CHAPTER 2. HOME RANGE AND HABITAT USE OF THE BLAINVILLE’S HORNED LIZARD (PHRYNOSOMA BLAINVILLII) IN THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA

Figure 1. Map of the Atwell Island and Semitropic Ridge study sites of P. blainvillii in the southern San Joaquin Valley, California ……………………………………...…………...52

Figure 2. Adult P. blainvillii with transmitter and mesh harness attached to dorsal side of the lizard ...... 53

Figure 4. Home range as determined by the 100% Minimum Convex Polygon (MCP) method of five Phrynosoma blainvillii at the Semitropic Ridge Preserve site, Kern County, California in 2010 ...... 55

Figure 5. Frequency of sightings of Phrynosoma blainvillii when above ground in five habitats at the Atwell and Semitropic sites in the southern San Joaquin Valley, California in 2010 . . 56

Figure 6. Frequency of sightings of male and female Phrynosoma blainvillii when above ground in five habitats at Atwell and Semitropic study sites in 2010 in the southern San Joaquin Valley, California ...... 57

CHAPTER 3. DEMOGRAPHICS, MORPHOLOGY, THERMOBIOLOGY, AND HABITAT PREFERENCE OF A POPULATION OF BLAINVILLE'S HORNED LIZARD IN THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA

Figure 1. Map of the study site, Atwell Island, in Kings County in the San Joaquin Valley, California, USA...... 88

Figure 3. Frequency distributions of snout-vent lengths of individual Phrynosoma blainvillii captured in April-November 2009 and 2010 at the Atwell Island study sites in the southern San Joaquin Valley, California, USA...... 90

Figure 4. Frequency of sightings of Phrynosoma blainvillii by time of day at the Atwell Island study site in the southern San Joaquin Valley, California, USA...... 91

Figure 5. Frequency of the substrate surface temperatures at which Phrynosoma blainvillii were active at the Atwell Island site in the southern San Joaquin Valley, California, USA ...... 92

CHAPTER 4. DIET ANALYSIS OF A POPULATION OF THE BLAINVILLE'S HORNED LIZARD (PHRYNOSOMA BLAINVILLII) FROM THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA, USA

Figure 1. Phrynosoma blainvillii fecal pellet collected from a population in the southern San Joaquin Valley, California...... 94

Figure 3. Composition of prey items found in 92 scats collected from a population of Phrynosoma blainvillii in the southern San Joaquin Valley, California ...... 96

INTRODUCTION

The Blainville’s Horned Lizard (Phrynosoma blainvillii), formerly named the Coast

Horned Lizard (P. coronatum, or P. c. frontale), occurs in southwestern and west-central

California (Fig. 1). Populations of this lizard have experienced severe declines throughout its

range (Goldberg 1983; Jennings 1987; Jennings and Hayes 1994; Fisher et al. 2002; Stebbins

2003), and it is listed as a California Species of Special Concern by the California Department of

Fish and Game (2011) and a Bureau of Land Management (BLM) Sensitive Species (2010).

Unlike other Phrynosoma species, especially the Texas Horned Lizard (P. cornutum), there has

been little field research published on demographics, home range, habitat use, or habitat

preferences of P. blainvillii; information that is critical in determining best practices for

conservation of this species.

The majority of the data that has been published on P. blainvillii consists of research

conducted on populations that occur in the southern portion of their range near San Diego, the

Los Angeles basin, and Riverside, and San Bernardino counties (Tinkham 1951; Goldberg 1983;

Hager 1992; Suarez et al. 1998; Fisher et al. 2002; Montanucci 2004). Even less studied are the

populations that occur in California’s San Joaquin Valley (Montanucci 1968; Tollestrup 1981;

Williams and Germano 1991), which are separated from their southern populations by the San

Emidgio mountain range. In light of their declining population, any research on P. blainvillii is

valuable to the species as a whole, but in terms of information on a regional scale, the

information collected from populations in southern California may not apply directly to those

populations inhabiting the San Joaquin Valley. This is because of the different habitat types found in each region, as well as the stark climate differences between the two regions. The

southern San Joaquin Valley experiences less rainfall, hotter summers, and cooler winters than

that of southern California (Western Regional Climate Center 2012; Germano et al. 2011).

Figure 1. Range of the Blainville’s Horned Lizard (Phrynosoma blainvillii), in California. The range extends into the northwestern tip of Baja California, Mexico (not shown). (Map modified from www.californiaherps.com)

It is in the San Joaquin Valley where arguably there is the greatest need for more information on the habitat requirements of the P. blainvillii due to the burgeoning human population growth rate and continued conversion of natural habitat to agricultural use. The

San Joaquin Valley is one of the world’s most productive agricultural regions and is the backbone of California’s agricultural industry (Galloway and Riley 1999). Human population growth in the Central Valley is predicted to occur at one of the fastest rates of any region in

California (California Department of Finance 2012). Expansion of agricultural activities and urbanization is ongoing, shrinking the already rare native lizard habitat. Indeed, in their report to the California Department of Fish and Game, Jennings and Hayes (1994) stressed that more effort needs to be focused on preserving areas, especially in the San Joaquin drainage basin, of remaining native plant community fragments that contain habitat that has never experienced significant substrate disturbance. Scientists and land managers are obligated to present their professional opinion on the impact these increasing pressures place on sensitive species such as the P. blainvillii. However, the lack of comprehensive data on the basic needs of P. blainvillii in the San Joaquin Valley results in an uncertain future for a species already experiencing dramatic population declines throughout its range.

RESEARCH OBJECTIVES

While there is an acute lack of information on all aspects of the general ecology of P. blainvillii that inhabit the San Joaquin Valley, I focused my research on two main objectives.

The first objective was to obtain baseline information on demographics, habitat use, and habitat preference. As native habitat in the San Joaquin Valley continues to dwindle, this type of

information is crucial to land managers in understanding the critical habitat requirements and

patterns of local distribution to ensure successful conservation of P. blainvillii populations in the

San Joaquin Valley. My second objective was to gain a better understanding of movement

ecology and home range size. Scientists have long known that to properly assess management

and conservation practices, it is critical to understand the fundamental behavior patterns such as

movement patterns. Movement patterns can give insight into the areas that contain essential

requirements such as food, cover, water, and mates (Burt 1943; Samuel and Fuller 1996). Areas

that contain these requirements are described as an animal’s home range (Burt 1943). Due to the

cryptic nature of this species, obtaining information on home range requirements is rather

difficult, and as a result, very little is known about their home range. In addition, I also gathered

information on activity patterns and dietary preferences based on scat analysis; information of

this type is an important contribution to the knowledge of general ecology of P. blainvillii in the

San Joaquin Valley.

The Blainville’s Horned Lizard has a long and complicated taxonomic history. There have been more than 20 attempts in over 100 years to demarcate the species (Leaché et. al 2009) resulting in articles, fact sheets, species accounts, and federal and state conservation status listings using a number of different common and scientific names when describing the horned lizard that is the focus of my research. In an attempt to provide clarity and decrease confusion stemming from multiple taxonomic changes, I will briefly review the taxonomic history, and in the interest of brevity, I will focus largely on the horned lizards of mainland California. In addition, because there is little information on P. blainvillii in general, I will review the known ecology, biology, further reasons for population declines, and conservation status of the species.

THE HORNED LIZARDS OF THE CORONATUM GROUP

Klauber (1936) presents a detailed examination of the historical taxonomic history

beginning with the first designation in 1835 by H.M.D. de Blainville and continuing in to the late

1930's. Confusion over taxonomic naming began shortly after the first designation; there are no

less than eight species and five subspecies descriptions by almost as many scientists for the

horned lizard collected from locales including the Cedros Island in Mexico, Baja California, and

mainland California west of the Sierra Nevada and as far north as San Francisco and Kennett,

California. The taxonomic debate centered upon whether a particular lizard population should be

considered a separate species, a parent species, or a subspecies and was based on geographic

location and morphologic characteristics. Klauber (1936) concluded that the horned lizards

populating mainland California are of the "blainvillii" group. He further separated the blainvillii

group into two subspecies: P. blainvillii frontale, which occupied California from San Francisco

and Kennet south to the coastal plain in Los Angeles and Orange counties, and P. blainvillii

blainvillii, whose range centered about San Diego and extended only from the San Bernardino

Mountains in San Bernardino County to the south approximately 80 km into the northern tip of

Baja California. Klauber (1936) classified the horned lizards that populated the rest of Baja

California and the Cedros Island as the Cape Region group, or "coronatum" group. Reeve

(1952) differed from Klauber’s view about California mainland horned lizards. It was Reeve’s opinion that those lizards occurring in central California should be designated as P. coronatum frontale and those lizards occurring in the southern counties of California should be designated

P. coronatum blainvillii. This taxonomy was adopted by Stebbins (1966) in the first field guide to western North American amphibians and reptiles. In 1994, Jennings and Hayes also used these scientific names and ranges in their report to the California Department of Fish and Game,

and used the common name California Horned Lizard for P. coronatum frontale and San Diego

Horned Lizard for P. coronatum blainvillii.

In discussing the importance of distinguishing species and subspecies in terms of

conservation, Brattstrom (1997) reviewed the characteristics that defined the two subspecies and

analyzed museum specimens from each group. Using the morphological characteristics that had

previously differentiated P. coronatum frontale and P. coronatum blainvillii, he determined that he could not distinguish the two subspecies; rather, he attributed the apparent differences between subspecies to the highly variable morphology of the species as a whole. Brattstrom

(1997) concluded that there were no valid subspecies of P. coronatum, the Coast Horned Lizard,

and that the previously described subspecies should be eliminated leaving only P. coronatum and

the common name Coast Horned Lizard.

In his investigation into allopatric speciation events in Baja California via ancient trans-

peninsular seaways in the Phrynosoma coronatum group, Montanucci (2004) analyzed 24

morphological and color-pattern characters of 634 specimens of Phrynosoma. He included specimens from throughout the range of P. coronatum in northern California to the southern tip

of Baja California. In contrast to Brattstrom’s conclusion that there should be only one species,

Montanucci (2004) concluded that there were four distinct species (including one new one): P.

blainvillii, P. cerroense, P. coronatum, and the newly named P. wigginsi. Montanucci (2004) hypothesized that only P. blainvillii occurs in mainland California and their range extends into nearly the entire northern half of Baja California. However, the current accepted hypothesis is that of Leaché et al. (2009). Using technological advances in mtDNA analysis from a single locus as well as morphometric and ecological niche analysis, Leaché et al. (2009) demonstrated that there are three ecologically divergent and morphologically diagnosable species within the P.

6 coronatum complex: P. blainvillii, P. cerroense, and P. coronatum. According to their delineation of ranges for each species, the only horned lizard that inhabits mainland California north of Mexico, including those in the San Joaquin Valley, is P. blainvillii. Because there are fact sheets, text books, articles, government listings, etc. that may be using different names based on the accepted name at the time of publication, it is hoped that information on the origin of the name will help to connect those past names to the currently accepted one, which is listed in the seventh edition of the Scientific and Standard English Names of Amphibians and Reptiles of

North America North of Mexico, with Comments Regarding Confidence in Our Understanding

(Crother 2012) as Phrynosoma blainvillii. Therefore, for all citations of studies on the horned lizard that occurred in mainland California, I will refer to them as Blainville’s Horned Lizard, P. blainvillii.

NATURAL HISTORY OF PHRYNOSOMA BLAINVILLII

Within its range, Phrynosoma blainvillii occupies a wide variety of habitats such as arid shrublands (low lying shrubs intermixed with forbs and grasses), annual grassland, coniferous forest, broadleaf woodland, coastal sage, and chaparral (Smith 1946; Jennings and Hayes 1994;

Sherbrooke 2003; Stebbins 2003). They can be found from sea level to approximately 2,000 m in elevation (Smith 1946; Jennings and Hayes 1994; Sherbrooke 2003; Stebbins 2003). Several important habitat elements seem to be necessary for P. blainvillii to thrive: loose, fine sandy soils where it can bury itself; an abundance of native ants and other insects; open areas with a limited amount of cover for basking, and areas of sparse grass that that does not hinder mobility

and scattered, low shrubs for cover (Jennings and Hayes 1994; Sherbrooke 2003; Newbold

2005).

MORPHOLOGY

Lizards in the family Phrynosomatidae include slim, round-bodied, long-legged lizards

such as those of the genus Callisaurus (zebra-tailed lizards), Uma (fringe-toed lizards) and

Sceloporus (spiny lizards), among others. However, several morphological traits set the genus

Phrynosoma apart from the other lizards in the family. Phrynosoma have a dorso-ventrally flattened body shape, which bears more of a resemblance to toads than to lizards, leading to people commonly referring to them “horny toads.” This body shape, along with short legs, results in their having a rather slow and awkward gait unlike the quick and graceful gait of other

Phrynosomatids. Other characteristics unique to most members of the genus Phrynosoma include 1) the presence of rigid cranial horns, 2) cryptic coloration that aids in their concealment, 3) their reluctance to run when approached, 4) a dietary preference for ants, 5) a tendency to have an unusually large stomach capacity for their size, 6) enlarged spiny scales that may appear on the dorsal surface and/or along the lateral fringe of the body, and 7) production of a large number of relatively small eggs or young (Pianka and Parker 1975; Sherbrooke 2003).

The genus Phrynosoma is made up of 13 species (Sherbrooke 2003), all of which are endemic to

North America. The Unites States has nine Phrynosoma species (Crother 2012) that are restricted to the Western U.S., particularly in the arid grasslands and deserts of western and central North America (Pianka and Parker 1975).

Phrynosoma blainvillii is one of four species of Phrynosoma that have a double row of abdominal fringe scales. It is one of the larger species of horned lizards with adults ranging from

64 mm to 114 mm snout to vent (SVL) length (Sherbrooke 2003; Stebbins 2003). Phrynosoma

blainvillii possess a crown of relatively longer temporal and occipital horns in which the first

three pairs do not touch at the base, and have three rows of pointed throat scales (Fig. 2).

Figure 2. A.) Terminology for selected characteristics of the left lateral features of the head of

Phrynosoma blainvillii. (1) Throat scales (only one row visible), (2) chin shields, (3) subrictal scale, (4) postrictal spine, (5, 6, 8, 9, 10) temporal horns, (7) temporal gap with reduced horn,

(11) occipital horn, (12) preoccipital tubercles. (Modified from Montanucci 2004). B.)

Photograph of chin shield and three rows of pointed throat scales on P. blainvillii from the

Atwell study site, Tulare County, California. (Photographed by Susan Hult).

The coloration of adult P. blainvillii is usually an overall brown, grayish, or reddish dorsal background with two large dark patches, referred to as saddles, on either side of the neck that are not widely separated from each other medially (Fig 3). There are no distinct color markings on the head or legs. Overall appearance in individual coloration and markings on the dorsal surface as described above varies only slightly from individual to individual, but local populations can vary widely and is generally in response to the substrate in which it blends in to.

The ventral side, however, varies to a greater degree among individuals and can range from those with very pale coloring to those that have a rich yellow (Fig. 4). Individuals can have many, few, or no spots on the belly that can be dark or fairly faint colored (Fig. 4).

Figure 3. Dorsal view of an adult Phrynosoma blainvillii in the southern San Joaquin Valley showing some of the identifying characteristics. Note the dark neck blotches giving a saddle-like shape, the wavy dark patches running transversely across the back, and long occipital and temporal horns. (Photographed by Susan Hult).

Figure 4. Ventral views of Phrynosoma blainvillii from the southern end of the San Joaquin

Valley, California showing variation in coloring and mottling. Coloration can range from pale to

deep yellow or reddish (not shown) and have few or many scattered spots, which may be faint

(left) or dark (right). (Photographed by Susan Hult).

Unlike many other lizards, horned lizards display obvious morphological differences

between the sexes (Smith 1946). Sex determination in P. blainvillii can be made externally by

observing the postanal scales, femoral pores, and the width of the tail base. In males, the

postanal scales are enlarged, the tail base is wider, and the femoral pores are more apparent than

in females (Fig. 5). An atypical trait in vertebrates, sexual size dimorphism occurs in which the

females are larger than the males in nearly all species of horned lizards (Zamudio 1998;

Sherbrooke 2003).

Figure 5. Photograph of a male and female P. blainvillii. Females (left) do not possess the enlarged postanal scales of males (circled; right). Also, note the wider tail base and more obvious femoral pores along the hind legs in the male. Photograph of individuals from the southern end of the San Joaquin Valley, California. (Photographed by Susan Hult).

ECOLOGY

Reproductive activity in horned lizards begins soon after spring emergence from hibernation, which is typically March or April (Howard 1974; Goldberg 1983; Jennings and

Hayes 1994). Horned lizards experience delayed maturation; that is, they are not sexually mature until their second or third year (Howard 1974; Pianka and Parker 1975; Jennings and

Hayes 1994) even though they have reached adult size by late summer of their first year (Pianka and Parker 1975). Reproductive cycles end in June for males and in July for females. Most literature reports P. blainvillii as laying a single clutch per season, but Goldberg (1983) reported a museum specimen containing the corpora lutea with yolk deposition in progress for a second clutch. Mating can last 15 to 30 min before the lizards separate and part ways (Sherbrooke

2003). Phrynosoma blainvillii are oviparous and lays an average clutch size of 11–13 eggs

(Howard 1974; Goldberg 1983; Jennings and Hayes 1994), although Stebbins (2003) listed the

average clutch size as 24–29 eggs. The female excavates a tunnel and begins egg deposition

usually in late May to June (Zeiner et al 1988; Jennings and Hayes 1994). She may stay close by

for a day or two, but does not stay the entire incubation period of approximately 60 days

(Howard 1974; Zeiner et al. 1988; Jennings and Hayes 1994). Hatchlings are precocial and have

the ability to perform all the activities of survival that adults do including food acquisition,

thermoregulation, and predator avoidance (Sherbrooke 2003).

Although the presence of a row of sharp cranial horns and spines on the back and lateral

sides of the body give P. blainvillii a rather ferocious appearance, they are actually docile. With

their wide, flattened body shape and short legs, they do not possess the ability to run away quickly for long distances to elude capture. Like most horned lizards, the first line of defense for

P. blainvillii is to avoid detection by predators. Avoiding predators has influenced some of the behavioral and physical adaptations of P. blainvillii (Klauber, 1936; Smith 1946; Sherbrooke

2003). Their cryptic coloration enables them to become nearly indistinguishable from the

substrate upon which they inhabit. The body shape is an adaptation that is advantageous for

camouflage in that a flattened body shape tends to cast very little shadow. The ventral spines

also help to break up the body outline. In addition, the behavioral adaptation of remaining

motionless rather than fleeing upon detection of danger makes horned lizards difficult to see

against the substrate (Klauber 1936; Smith 1946; Sherbrooke 2003). In the event that a predator

does get too close, their second line of defense is to run short distances to seek cover or to re-

establish crypsis (Smith 1946; Sherbrooke 2003). If camouflage and fleeing fail, they have been

known to hiss and jump at potential threats, gulp air to appear larger, and jab with their horns

(Smith 1946; Milne and Milne 1950; Sherbrooke 2003; Stebbins 2003). One of the most unusual behaviors, unique to most species of horned lizards, is their ability to squirt a narrow stream of blood from their eyes. They can project the stream forward or backward and reach distances of up to almost 2 m (Smith 1946; Cutter 1959; Sherbrooke 2003). It was first believed that blood squirting would startle or distract a predator into dropping the lizard allowing it to escape (Hay

1892). However, several articles reported that canids in particular elicited this reaction more than any other predators (Burleson 1942; Smith 1946; Reeve 1952; Middendorf III and

Sherbrooke 1992) and are repulsed by compounds in the blood rather than the act of squirting itself (Middendorf III et al. 2001). Known predators of P. blainvillii include mammals such as

Badgers (Taxidea taxus), foxes, Coyotes (Canis latrans), and house pets such as dogs and cats.

Birds that are known to prey on P. blainvillii include Greater Roadrunner (Geococcyx californianus), Loggerhead Shrike (Lanius ludovicianus), American Kestrel (Falco sparverius), and Burrowing Owl (Athene cunicularia; Zeiner et al. 1988; Jennings and Hayes 1994). The

Northern Pacific Rattlesnake (Crotalus viridis oreganus) has also been known to prey on P. blainvillii (Zeiner et al. 1988; Jennings and Hayes 1994). Grant and Alberts (2001) and Labonte

(2001) have both confirmed P. blainvillii predation by Coachwhips (Masticophis flagellum).

Phrynosoma blainvillii are insectivorous and, typical of the genus, have a diet that consists primarily of ants, particularly native harvester ants (Pogonomyrmex spp.; Reeve 1952; Jennings and Hayes 1994; Sherbrooke 2003). Although ants can make up to 90% of the lizard’s diet, P. blainvillii is one of only a few members of the genus that have a more varied diet in which they will also consume other insects in abundance, such as beetles, flies, spiders, grasshoppers, moth larvae, and even honeybees (Milne and Milne 1950; Montanucci 1989; Sherbrooke 2003).

Horned lizards are active foragers seeking out ant colonies or foraging ant trails, but once ants

are located, these lizards adopt a sit-and-wait approach and capture prey by flicking their tongue out and quickly swallowing it (Suarez et al. 2000; Sherbrooke and Schwenk 2008).

FACTORS AFFECTING POPULATION ABUNDANCE

Phrynosoma blainvillii populations have experienced severe declines throughout its

range, leaving some locales of formerly abundant populations nearly or completely absent of

lizards (Goldberg 1983; Jennings 1987; Jennings and Hayes 1994; Fisher et al. 2002; Stebbins

2003). In addition to habitat degradation and loss, other factors have been identified as likely

causes of population declines. Human exploitation has had a major impact on P. blainvillii

populations. Jennings (1987) presents a detailed account as to how the collection of massive

numbers of the lizards in the early 1880’s to the 1930’s from southern California as novelty

items to be sold as souvenirs or pets contributed to a rapid decline of these lizards. In the same

report, Jennings makes note of the life histories that make them very susceptible to over-

collection such as laying a single clutch of 11–12 eggs per year and late maturation as well as

possibly low survivorship of young. Biological supply companies also exploited P. blainvillii

populations, and in 1981, commercial collecting was banned (Jennings and Hayes 1994).

One of the most problematic factors involved in reduction of P. blainvillii numbers is

proliferation of exotic ants in P. blainvillii habitat (Jennings and Hayes 1994; Fisher et al. 2002;

Suarez and Case 2002). Argentine Ants (Linepithema humile) are commonly found in disturbed

areas, especially around urban development (Knight and Rust 1990) and fragmented habitats

where they are most abundant along edges (Suarez et al. 1998). Indeed, Knight and Rust (1990)

reported that Argentine Ants was the most common urban ant pest in four regions in California

and that they are extending their range within California. The Argentine Ant is problematic for

15 the lizards in two ways. First, it greatly reduces and even eliminates the lizard’s main prey, native harvester ants (Pogomyrmex and Messor spp.) after invasion (Suarez et al. 1998; Suarez et al. 2000). They accomplish this with their ability to quickly establish colonies and outnumber native ants (Erickson 1971). Argentine Ants do not tolerate the presence of other ant species and will eliminate them by aggressively monopolizing food resources and by attacking and killing the larger harvester ant when they are vulnerable, usually in cooler temperatures when the harvester ants are sluggish (Erickson 1971; Suarez et al. 1998). Second, after displacing native ant species, studies have shown that Argentine Ants are not a suitable replacement prey items for

P. blainvillii. In laboratory experiments where invaded communities were simulated, hatchling horned lizards exhibited negative or near zero growth rates (Suarez and Case 2002). Other studies on prey selection reveal that adult and juvenile horned lizards avoid eating Argentine

Ants despite their availability. They are forced to incorporate less abundant and harder to find non-arthropods into their diet (Suarez al. 2000; Fisher et al. 2002). In addition to the Argentine

Ant, the Red Imported Fire Ant (Solenopsis invicta) has also invaded areas within P. blainvillii range. The Red Imported Fire Ant has a severe impact on native ant communities, most likely through competitive replacement (Porter and Savignano 1990). Native ant abundance and diversity drops significantly in invaded areas as does non-ant arthropod communities (Porter and

Savignano 1990). The presence of exotic ant invasions affects the trophic system and has a devastating indirect effect on horned lizards, resulting in the reduction or elimination of horned lizard populations (Porter and Savignano 1990; Jennings and Hayes 1994; Suarez et al. 2000;

Fisher et al. 2002; Suarez and Case 2002).

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California Department of Fish and Game.

HOME RANGE AND HABITAT USE OF THE BLAINVILLE’S HORNED LIZARD (PHRYNOSOMA

BLAINVILLII) IN THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA

1 SUSAN M. HULT AND DAVID J. GERMANO

Department of Biology, California State University, Bakersfield, California 93311

Present address of SMH: 7356 394th Street, North Branch, Minnesota 55056

1Correspondent email: [email protected]

Abstract.—The Blainville’s Horned Lizard (Phrynosoma blainvillii) has declined throughout

its range and is listed by the California Department of Fish and Game as a Species of

Special Concern. Understanding home range and above ground habitat use can be

important to their conservation. We initiated a radio-telemetry study in 2010 at two study

sites in the southern San Joaquin Valley within 40 kilometers of each other, but with

slightly different habitat characteristics. We calculated home range size from 10 lizards,

five at each site. We used the 100% Minimum Convex Polygon (MCP) and the Fixed-K

Local convex hull (LoCoH) home range estimators for comparative purposes. Home range sizes determined by the 100% MCP estimator ranged from 0.58 ha to 13.93 ha. The average home range size for lizards at the Semitropic Ridge Preserve site was 7.28 (±2.74

SE) ha and at the Atwell Island site was 2.68 (±0.69 SE) ha. There was no significant difference in average home range size between the sites. The Fixed-K LoCoH method produced similar home range estimates as the 100% MCP method. When above ground and active, P. blainvillii at either site used areas of bare ground more often than expected

23 based on equal use. At the Semitropic site, the lizards used areas under shrubs almost as often as bare ground, while at the Atwell site the lizards used areas of sparse vegetation more often than expected, but not as much as bare ground. Lizards at both sites used medium-dense and dense areas of vegetation much less than expected based on equal use.

Key Words.—conservation; fixed-k LoCoH; management; minimum convex polygon; telemetry

INTRODUCTION

The Blainville’s Horned Lizard (Phrynosoma blainvillii), formerly named the Coast Horned

Lizard (P. coronatum or P.c. frontale), is endemic to California and the northwestern corner of

Baja California, Mexico (Stebbins 2003; Leaché et. al 2009). The western edge of its range extends along the northern tip of the Pacific coast of Baja California to the San Francisco Bay.

Historically the northern edge of its range reached as far north as Kennett, California but that area is now under the Shasta Reservoir (Stebbins 2003). Now the northern edge is considered to be Butte County, California where it occurs on the edges of the Sacramento Valley (Stebbins

2003). The eastern reach of its range is the western side of the Sierra Nevada and remains west of the deserts in southern California (Stebbins 2003).

Populations of this species have experienced severe declines throughout its range, leaving some locales of formerly abundant populations nearly or completely absent of lizards (Goldberg

1983; Jennings 1987; Jennings and Hayes 1994; Fisher et al. 2002; Stebbins 2003) and are listed as a California Species of Special Concern (California Department of Fish and Game. 2011.

Available from http://www.dfg.ca.gov/wildlife/nongame/ssc/amphibian-reptile.html. [Accessed

22 September 2011]) and a Bureau of Land Management Sensitive Species (Bureau of Land

Management. 2010. California-BLM Sensitive Animals. Accessed online at

http://www.blm.gov/ca/st/en/prog/wildlife.html. [Accessed 19 September 2010]). There is

evidence that P. blainvillii was once abundant within its range in southern California; during a

period of 30 years (1890–1910) an estimated 100,000 were collected by people involved in the

curio trade (Jennings 1987). However, in the following 30 years (1910–1930) the estimated

number of lizards collected dropped to 10,000 in part due to over-exploitation and extensive

habitat destruction and urbanization (Goldberg 1983; Jennings 1987). Anecdotal evidence in the

form of citizens reporting that they no longer see P. blainvillii in great numbers as they once did

is commonplace throughout their range. Several explanations have been put forth as to the cause

of population declines. Livestock overgrazing, off-highway vehicle use, fires, water diversion structures, and conversion of native habitat to vast tracts of agricultural commodities certainly contribute to habitat degradation and loss in which the lizards are unable to survive (Goldberg

1983; Jennings and Hayes 1994; Stebbins 2003). Pesticide use in conjunction with agricultural activity kills harvester ants (Pogonomyrmex and Messor spp.), the preferred prey of horned lizards (Suarez and Case 2002; Stebbins 2003; Sherbrooke 2003). The proliferation of the non- native ants such as the Argentine Ant (Linepithema humile) and the Red Imported Fire Ant

(Solenopsis invicta) has been associated with loss of harvester ants as well. For example, upon establishment of a colony, Argentine Ants proceed to eliminate adjacent native harvester ant colonies (Erickson 1971; Suarez et al. 1998). Once the harvester ants have been eliminated,

Argentine Ants do not serve as suitable replacement prey because adult horned lizards avoid consuming them and juvenile horned lizards fail to thrive on a diet of these ants (Suarez and

Case 2002). The burgeoning human population and expansion into ever-decreasing horned lizard habitat also contributes to the decline in horned lizard populations through habitat

25 fragmentation, direct mortalities on roads, and introduction or expansion of predators into horned lizard habitat (Jennings 1987; Jennings and Hayes 1994; Stebbins 2003; Audsley et al. 2006).

For a species such as P. blainvillii in the southern San Joaquin Valley, whose population seems to be in decline for reasons poorly understood (they are not in decline in some areas for which the habitat seems appropriate), understanding why they are found in particular locales and quantifying how much land they need to survive in these locales are critical aspects in developing management and conservation plans. One useful ecological parameter of many mobile species is its “home range.” The home range is most commonly defined as being the area over which an animal normally travels in pursuit of its routine activities to meet the requirements for survival, growth, and reproduction (Burt 1943; Rose 1982; White and Garrot 1990). Thus, many conservation plans use home range data to aid in determining how much space needs to be conserved and what habitat components within that space are critical.

Unlike other Phrynosoma species, particularly P. cornutum, the Texas Horned Lizard, there have been comparatively few field research studies published on the general ecology of P. blainvillii. Most studies on P. blainvillii have been on populations that occur in the southern portion of their range (Goldberg 1983; Hager and Brattstrom 1997; Suarez et al. 1998; Fisher et al. 2002; Montanucci 2004), with one behavioral (Tollestrup 1981) and one ecological (Gerson

2011) study in the San Joaquin Valley. The populations occurring in the San Joaquin Valley are separated from their southern California populations by the Transverse mountain ranges.

Information collected from populations in southern California may not apply directly to those populations inhabiting the San Joaquin Valley due to the different habitat types and climates of each region. Much of the San Joaquin Valley is a desert, especially the western and southern two thirds (Germano et al. 2011), which experiences less rainfall, hotter summers, and cooler

winters than that of southern California (Western Regional Climate Center. 2012. Cooperative

climatological data summaries. NOAA cooperative stations-temperature and precipitations. C.

California and S. California. Available from http://www.wrcc.dri.edu/climatedata/climsum

[Accessed 10 September 2012]).

To gain a better understanding on the home range ecology and habitat use of P. blainvillii in

the southern San Joaquin Valley, we initiated a telemetry study to serve as baseline information

that can be incorporated into the decision-making processes for the conservation of habitat, and

ultimately, conservation of this state-protected species. The primary objective of this study was

to determine home range size as a guideline as to how much land would be optimal to conserve.

The secondary objective was to determine microhabitat use, which can be more clearly

documented with the use of telemetry than past efforts relying on chance encounters.

MATERIALS AND METHODS

Study sites.—We conducted research at two sites in the southern San Joaquin Valley: Atwell

Island on Bureau of Land Management (BLM) land near Alpaugh, in southeastern Kings

County, and the Semitropic Ridge Preserve managed by the Center for Natural Lands

Management, located 24 kilometers northwest of Wasco, Kern County, California (Fig. 1). At the Atwell island site, two locations were sampled, both of which straddled the shoreline and the sand ridge of the former Tulare Lake, thus it contains soils typical of lacustrine deposits as well as the loose sandy soils. At Location 1, referred to as "the pasture," we surveyed for lizards in a fenced 156 ha parcel that had been seasonally grazed by cattle for many years. Within the pasture, there were five soil series and their associated habitat series. Westcamp loam,

Westcamp silt loam, and Excelsior fine sandy loam comprised approximately 47% of total area

and supports the Seepweed Series habitat (Sawyer and Keeler-Wolf 1995; Soil Survey Staff,

Natural Resources Conservation Service, United States Department of Agriculture. Web Soil

Survey. 2009. Available from http://websoilsurvey.nrcs.usda.gov. [Accessed 10 September

2009]). The dominant shrubs in this area were Bush Seepweed (Suaeda moquinii) and Alkali

Heath (Frankenia salina), while Saltgrass (Distichlis spicata) and non-native annual grasses

(Bromus spp.) were the dominant grassland species present. Spikeweed (Centromadia pungens) and Goldfields (Lasthenia californica and L. minor) were other dominant plant species (Table 1).

The Sandridge loamy fine sand and Posochanet silt loam, which comprised approximately 53% of the total area, supports the California Annual Grassland habitat series (Sawyer and Keeler-

Wolf 1995; USDI, unpubl. report). A mixture of non-native and native annual grasses typically dominates this habitat series (Sawyer and Keeler-Wolf 1995). However, cattle grazing occurred throughout the pasture and the dominant vegetative structure were the shrubs Goldenbush

(Isocoma acradenia) with a few Valley Saltbush (Atriplex polycarpa), and the forbs Fiddleneck

(Amsinkia menziesii), Broadleaf Filaree (Erodium botrys), and Spikeweed (Centromadia pungens). Non-native annual grasses (e.g., Bromus spp.) were present, but were generally grazed or trampled down.

Throughout the first location, the pasture, there were many large open spaces with little or no

vegetative structure due to cattle grazing, the natural senescence of herbaceous vegetation as the

season became hotter and drier, and an abundance of soil mounds created mostly by Heermann's

(Dipodomys heermanni) kangaroo rats. Sympatric lizards in the pasture included the California

Whiptail (Aspidoscelis tigris munda) and Western Side-blotched Lizard (Uta stansburiana

elegans). The overall topography was mostly level at an elevation range of 61–66 m above sea

level. The land surrounding the pasture was formerly cultivated fields that were fallow or had

28 undergone habitat restoration treatments in the years preceding our study. Unlike the immediately surrounding areas, the pasture had not undergone significant substrate disturbance such as canal or road development, deep disk plowing, or laser leveling. Based on visual estimates and aerial imagery, we characterized the overall microhabitat of the pasture as 30% dense vegetation, 25% bare ground, 20% shrubs, 15% sparse vegetation, and 10% medium dense vegetation.

The second location (Location 2) at the Atwell Island site was a 120 ha area adjacent to and southwest of the pasture, but separated by an unlined irrigation (Poso) canal. This area was not fenced in and we delineated the boundary based on soil type, vegetative communities, roads, and reports of historical horned lizard sightings. This location had been cultivated with grain crops until the late 1980s and had been fallow since that time. Despite the agricultural activity,

Location 2 had also never undergone laser leveling or deep disk plowing (USDI, unpubl. report).

There was never a grazing regime at this location with the exception of an occasional sheep trespass. The soil types and associated vegetative communities were similar to the pasture.

However, because of the decades of inactivity, all of the soil series and associated vegetative communities in Location 2 were dominated by dense areas of non-native annual grasses (Bromus spp.) with fewer scattered patches of shrubs and forbs. An unpaved and rarely used road bisected Location 2 and this was the main source of open space and bare ground. Aside from the road, a few rodent burrows scattered throughout the location provided areas of bare ground and sparse herbaceous vegetation. There were narrow trails formed by Desert Cottontails (Sylvilagus auduboni), Black-tailed Jackrabbits (Lepus californicus), and Heermann's Kangaroo Rats in the dense grass. The Western Side-blotched Lizard and the California Whiptail were the only other lizard species we observed at this location. Based on visual estimates and aerial imagery, the

overall habitat in this location as 80% dense grassland, 10% bare ground, 5% shrubs, 5%

medium dense herbaceous vegetation, and < 5% sparse herbaceous vegetation.

The study location at the Semitropic Ridge Preserve encompassed approximately 400 ha.

The Semitropic Ridge Preserve encompasses one of largest natural remnants of native habitat in the San Joaquin Valley. Our study site was dominated by Spiny Saltbush (Atriplex spinifera),

Red Brome (Bromus madritensis rubens), Spikeweed (Centromadia pungens), Goldfields

(Lasthenia californica), and Fiddleneck (Amsinkia menziesii). There were large patches of open

areas in the form of alkali playas and scalds characterized by bare ground with patches of white,

crusty soil intermingled throughout the study area. Soils at this site were compact, primarily

moderately well drained to well-drained silt loam (Soil Survey Staff, Natural Resources

Conservation Service, United States Department of Agriculture. 2009. op. cit.). We characterized the microhabitat as 50% sparse vegetation, 20% shrubs, 15% bare ground, 10% dense vegetation, and 5% medium dense vegetation. The topography was nearly level with an elevation range of 72–73 m above sea level.

Field methods.—We conducted research from 16 March to 7 September 2010 concurrently at

the Atwell Island site and the Semitropic site. We located lizards using meandering transects and

chance encounters and we captured them by hand. Most searches occurred between 0800 and

1200 to coincide with peak activity (Heath 1965; Pianka and Parker 1975; Hager and Brattstrom

1997), although some searches occurred in the afternoon. When captured, we recorded the date,

time of day, and the capture location using Global Positioning System (GPS) in the WGS 1984

coordinate system obtained by a Magellan MobileMapper CX GPS Unit (Magellan, Santa Clara,

California, USA). We also recorded standard morphometric data: snout-vent length (SVL) and

tail length (TL) to the nearest millimeter and mass (to 1 g) using a spring scale (PESOLA, Baar,

Switzerland). We determined the sex of the lizard based on the presence of enlarged post-anal

scales and conspicuous femoral pores that are indicative of males.

We fitted adult lizards of a certain size (≥ 25 g) with radio-transmitters (SOPR-2070; 2.2–2.7 g; battery life 19 weeks; Wildlife Materials, Inc. Murphysboro, Illinois) using a mesh harness glued to the lizard to help secure the transmitter to the lizard (Fig. 2; Warner et al. 2006). During the course of the study, however, we discovered that arms of the mesh harness would often come loose and detach from the lizard despite several attempts of re-gluing them back on in the field.

Therefore, in the later part of the study, we ceased using the mesh harness and simply attached the transmitter to the lizard directly using only non-toxic silicone glue. We spread a few drops of clue to the top of the transmitter and sprinkled sand over it to avoid disrupting the camouflage design of the lizard. We trimmed the antenna so it projected 5 cm beyond the length of the lizard to reduce the chance that it might interfere with movement on the lizards as they navigated in rodent burrows. When attaching the transmitter, we kept the lizards in a small enclosure until the silicone glue was dry, and then released them at their exact capture location. The weight of the transmitter package (2.5 g) ranged from 6–10% of the lizard’s mass at the time of capture.

Although the transmitter weights were greater than the 5% typically recommended, we did not see a difference in movement of lizards to those without transmitters, so we believed that the transmitter did not affect movement or survival.

We radio-tracked the lizards using a radio telemetry receiver (R-1000 Telemetry Receiver;

Communications Specialists, Inc., Orange, California) and a three element folding Yagi-Uda antenna (Model # F165-3FB AF Antronics, Inc. Urbana, Illinois). The reception range of this equipment, with the snipped transmitter antennae, ranged from approximately 320 m when the

lizard was underground to approximately 800 m when it was above ground. The topography at

the Atwell and Semitropic sites is nearly flat and there are no obstacles such as large trees or

hills, thus range detection was optimal. We tracked lizards 5–7 days a week, keeping a

consistent sampling scheme of at least a six-hour time lapse between observations to eliminate dependency among observations. Autocorrelation, or a lack of independence of observations, is commonly emphasized as problematic because they produce biased estimates of home ranges, particularly among home range estimators that use statistical hypothesis testing such as kernel estimators (Swihart and Slade 1985; de Solla et. al. 1999; Fair and Henke 1999; Row and

Blouin-Demers 2006). For herpetofauna such as P. blainvillii that do not move frequently and often use a particular location repeatedly (Row and Blouin-Demers 2006; pers. obs), autocorrelation is very likely to occur. However, Row and Blouin-Demers (2006) believe the

MCP method, which is a non-statistical method, is the most accurate method for herpetofaunal studies that wish to focus on home range size and not density of use. Additionally, Swihardt and

Slade (1997) affirmed that avoiding autocorrelation is unnecessary when estimating home range sizes with polygon methods and de Solla et. al (1999) established that as long as observations are recorded at regular intervals, autocorrelation should not be a serious issue. Because of these observations, we were confident in obtaining an accurate estimate of home range size using MCP with observations made at intervals of at least six hours apart.

For each observation we recorded the date, time of day, climatic conditions, and ground temperature. All lizards were tracked until one of the following occurred: (1) the transmitter was found on the ground detached from the lizard in an undetermined manner, (2) the lizard sloughed its skin along with the transmitter, (3) the transmitter signal was abruptly undetectable

32 and an extensive search of an approximately 1.5 km radius around the study area for three days proved unsuccessful, or (4) lizards were found dead.

We recorded the microhabitat characteristics within a 1 m circular area at each lizard encounter. We used the capture location as the center point of the circular area. We measured the distance to the nearest shrub and/or to the nearest patch of herbaceous vegetation, which was either a conglomerate of grass and forbs or one or the other. We also took a photograph of the location. The vegetative cover was determined by ocular estimates taken at the time of each lizard observation or by examining the photographs of the encounter area after the field study.

We categorized the microhabitat features of the precise location where the lizard was encountered as (1) bare ground: including “cow pies” (dried domestic bovine manure), sandy patches with no herbaceous vegetation or sandy patches with very few stems and trampled grass; the vegetation in this category was considered not to impede lizard locomotion, (2) shrub: the lizard was seeking cover under a shrub; in some cases there was some herbaceous vegetation mixed in the shrubs (3) sparse: herbaceous vegetation provided 1–20% of cover, (4) medium dense: herbaceous vegetation provided 20–50% cover, (5) dense: herbaceous vegetation provided 50–100% cover. If the lizards used a habitat feature more than its availability, we considered the lizards to be selecting for it. Likewise, if the lizards used a habitat feature less than its availability, we considered it avoided by the lizards.

Data analysis.—We entered the geographic coordinates for all lizards into the ArcMap function of ArcGIS v. 9.2 software (Environmental Systems Research Institute, Redlands,

California). For lizards with > 19 relocation points, we calculated home ranges using two estimators: the minimum convex polygon (MCP) method (Mohr and Stumpf 1966) using the

Hawth’s Analysis Tools for ArcGIS v. 3.27 (Beyer, H. L. 2004. Hawth's Analysis Tools for

ArcGIS) and the local nearest-neighbor convex-hull (LoCoH; also known as k-NNCH; Getz and

Wilmers 2004) using the Fixed-K LoCoH algorithm on the LoCoH web application (available from http://locoh.cnr.berkeley.edu/). LoCoH requires the user to choose a value for k, which is the number of nearest neighbors LoCoH will use to construct a convex hull. The web interface tutorial suggests two steps in determining a suitable k value. The first step is to experiment with different values for k. A graphical representation of the observation points and the hulls generated around them is produced for each k value. Taking into consideration the landscape and natural history of your animal, it is suggested to narrow your choice to the value of k that generates a home range coverage that is neither too small nor too large. The second step is to use the "Area Covered vs. k" option, which generates a graph of the home range area vs. k. The graph reveals a linear version of how the area covered by the home range changes as k changes.

Important k values to consider are those in which there are large “jumps” between k values,

indicating that the home range has started to cover a large portion of previously uncovered area.

Values for k below the jump likely produce home ranges that are too small and values for k

above the jump likely produce home ranges that are too large. Together with the graphical

representations generated in step 1, you choose the k value in the jump area that appears to

produce the best home range area for your data. We followed this procedure to determine the

best k value for each lizard. Our data had locational points very near or on top of each other that

the LoCoH program may perceive as a duplicate point, so to ensure that all data points were

considered in the analysis, we chose to displace duplicate points by one unit in a random

direction.

The MCP method is sensitive to outlying points, and including them in the area when maybe

the outliers should not be included can result in overestimates of true home ranges. These

outliers can be the result of an animal’s exploratory movement rather than a movement necessary

for survival and reproduction, or, prior to the use of GPS technology to obtain points,

triangulation errors. Outliers are generally removed without biological basis, thus contributing

researcher bias into the results and as a result might not provide a repeatable home-range estimate among different researchers (Samuel and Fuller 1996). To reduce bias in excluding outliers, many researchers choose to use the polygon that surrounds 95% of the total area and report it as the 95% MCP. When we examined our data, only three of the 10 lizards had any points that could be considered outliers, and in each case, it was only one point. Therefore, we chose to eliminate the one point for each lizard and report the 100% MCP for all home range estimates.

To determine if home range sizes differed between the Atwell and Semitropic sites, we used a two-sample t-test with unequal variances on log-transformed data. We used a One-way ANOVA test to determine if the method used to estimate home range sizes, (Fixed-K LoCoH and MCP) calculated significantly different home range sizes. We did not test for sex differences by site in home range size because we did not have enough locations for all females to determine an accurate home range. To determine if the use of microhabitats by P. blainvillii was the same between Atwell and Semitropic sites, we used a Contingency Table analysis. We compared microhabitat use within a site using sequential Chi-square. We also compared the use of microhabitats by males and females, irrespective of site, using a Contingency Table, followed by sequential Chi-square. In a 2009 study of P. blainvillii habitat preference (Hult and Germano, unpubl. data), we collected data on habitat use, but the data was from non-telemetered lizards at

the Atwell study location only. Because we were aware that sightability might be an issue and

result in a bias toward finding lizards in open habitat, we compared the data from the 2009 non-

telemetered lizards to the data from this study using the same statistical tests. The results from

this study on telemetered lizards will either affirm or refute our findings from the 2009 habitat

use data. We did not include the data from the non-telemetered lizards in analysis when we

performed comparison analyses between Atwell and Semitropic. We used Minitab 16 statistical

software (Minitab Inc., State College, Pennsylvania, USA) to run Contingency Tables, One-Way

and two-sample t-tests. For all tests, α = 0.05.

RESULTS

We fitted 14 P. blainvillii with transmitters; five females and two males at the Atwell site and

four males and three females at the Semitropic site (Table 1). The number of locations captured

for the seven lizards at the Atwell site ranged from three to 64 and for the Semitropic site from

five to 69 (Table 1). Of the 14 lizards fitted with transmitters, 10 (five at each site) had ≥ 19

observations. We used these 10 to calculate home range sizes (Table 1, Table 2). The mean (±

SE) home range size based on the 100% MCP method of the five lizards at the Atwell site was

2.68 (± 0.69) ha with a range of 0.87 to 4.24 ha (Table 2; Fig.3) and the mean home range size of

the five lizards at the Semitropic site was 7.28 (± 2.74) ha with a range of 0.58 to 13.93 ha (Table

2; Fig.4). The mean home range using the Fixed-K LoCoH method was 2.53 (± 0.69) ha with a range of 0.59 to 3.99 ha at the Atwell site and 6.91 (± 2.64) ha with a range of 0.55 to 13.41 ha at the Semitropic site (Table 2). Although the mean home range size at the Semitropic site was almost three times larger than the mean size at the Atwell site, the differences were not

significant when calculated by either the MCP method (t = -1.63, P = 0.179) or the Fixed-K

LoCoH method (t = -1.60, P = 0.184). Regardless of the site, the average home range size of all

lizards (n = 10) based on the 100% MCP method was 4.98 ha (± 1.54).

Phrynosoma blainvillii differed significantly in their use of microhabitats between the two sites

(χ2 = 35.78, df = 4, P < 0.001). At the Atwell site, lizards did not use microhabitats equally (χ2

= 53.94, df = 4, P < 0.001); we found them significantly more often in areas of bare ground and

sparse vegetation than in areas with medium or dense herbaceous vegetation or under shrubs (χ2

= 53.70, df = 2, P < 0.001; Fig. 5). Horned lizards were found equally as often in areas of

medium or dense herbaceous vegetation or under shrubs (χ2 = 0.491, df = 2, P = 0.782), and

differed significantly between areas of bare ground and sparse vegetation (χ2 = 8.35, df = 1, P =

0.004). These data mirrored the findings from the 2009 non-telemetered lizard data. The data

from 2009 showed lizards did not use microhabitats equally (χ2 = 212.50, df = 4, P < 0.001). We found them significantly more often in areas of bare ground and sparse vegetation than in areas with medium or dense herbaceous vegetation or under shrubs (χ2 = 63.09, df = 2, P < 0.001), and

that they were found equally as often in areas of medium or dense herbaceous vegetation or

under shrubs (χ2 = 2.86, df = 2, P = 0.240). The lizards in 2009 also significantly differed

between areas of bare ground and sparse vegetation (χ2 = 17.07, df = 1, P < 0.001).

The lizards at the Semitropic site also did not use microhabitats equally (χ2 = 163.53, df =

4, P < 0.001; Fig. 5). We found them significantly more often in areas of bare ground and under shrubs than in areas with either sparse, medium, or dense herbaceous vegetation ( χ2 = 512.04, df

= 2, P < 0.001). The lizards were found equally as often in areas of bare ground and under

shrubs (χ2 = 0.151, df = 2, P = 0.658), and equally as often in medium and dense herbaceous vegetation (χ2 < 0.001, df = 2, P = 1.00). Irrespective of site, males and females used

microhabitats similarly (χ2 = 8.20, df = 2, P = 0.084; Fig. 6). Regardless of sex or site, P.

blainvillii differed in their overall use of microhabitats (χ2 = 180.51, df = 4, P < 0.001), with

medium and dense cover used equally as often (χ2 = 0.129, df = 2, P = 0.719), but with bare

ground, under shrubs, and sparse vegetation differing significantly in their use (χ2 = 7.50-49.82,

dfs = 2, P = 0.006 to < 0.001). Overall, we found horned lizards most often on bare ground, then

under shrubs, then in sparse vegetation, and least often in medium and dense herbaceous

vegetation (Fig. 5).

DISCUSSION

Home range of P. blainvillii.—The mean home range size (5.0 ha) for P. blainvillii in the

southern San Joaquin Valley is larger than the mean adult home range of 0.094 ha calculated by

Hager (1992) of P. blainvillii in San Bernardino and Riverside counties in southern California. It should be noted that Hager’s home range estimates are derived from four adult lizards (three males, one female) as calculated by minimum convex polygon method using rather low numbers

(14–25) of locations. In another study on P. blainvillii in southern California, lizards had a mean home range of 10 ha (Fischer et al. 2002). This value falls within the range of our home range estimates for our study site; however, Fisher et al. (2002) fails to mention any specifics such as the estimator used or the number of lizards and sightings so it is not clear how reliable their estimates are. The area of land that is optimal for P. blainvillii conservation across its range is not possible to robustly estimate with the data that are currently available.

Phrynosoma blainvillii at the two sites in the southern San Joaquin Valley had a rather large variation in home range size (0.58–13.93 ha). This suggests that although we can determine an

overall mean estimate of home range size, the mean size should not be used as the amount of

land to conserve. Some individual lizards used a small area, whereas others used much larger

areas in a season. Keeping in mind that conservation plans generally set aside more habitat than

is needed for individuals, the importance of these data are that they provide an order of magnitude of home range size. Phrynosoma blainvillii appear to have seasonal and yearly shifts in home range size (Hager 1992). Fair and Henke (1999) found that P. cornutum also has a seasonal shift in home range size. Other factors that affect home range size in lizards include seasonal climatic changes, habitat productivity, lizard density, predator abundance, lizard sex, and social factors such as behavioral changes during the breeding season (Rose 1982; Christian and Waldschmidt 1984). Our study occurred over one season from spring until fall and thus may not detect shifts in home range size. Therefore, it may be difficult to define an optimal amount of land that would be suitable for P. blainvillii in the San Joaquin Valley. Our study provides a baseline for further studies that need to take place over a number of years, which should include larger sample sizes, occur in changing climatic conditions, and with various levels of food resources.

There are numerous home range estimators available for calculating home range area, each with their own strength and weaknesses, which can produce substantially different results

(Samuel and Fuller 1996). Because of this, we wanted to test the two estimators to see if one produced a significantly different result than the other. The minimum convex polygon (MCP) method is one of the oldest and most commonly used methods of home range estimation making it useful for comparative studies. One critique of the MCP method is that it cannot distinguish areas within the outermost convex polygon that the animal does not use; therefore, it creates an overestimation of the actual home range. The LoCoH estimator is a relatively new method

developed by Getz and Willmers (2004) that builds on MCP by also creating convex polygons

around a set of data points, but has the ability to eliminate areas within the polygons that are not

used by the animal. For example, a body of water within a lizards' home range would be an area

not used and therefore the area encompassing the body of water would be excluded from

analysis. For this reason it has been suggested that LoCoH can be a more accurate assessment of

true home range (Getz and Wilmers 2004; Getz et al. 2007). However, we found that the LoCoH

estimator did not produce home range estimates that were significantly different from the MCP

method. This is most likely due to the topography of our study sites. Within the lizard’s home

range there were no obstacles such as bodies of water, rock outcrops, or building structures that

the lizards would avoid, thereby eliminating the proposed advantage of the LoCoH estimator.

Factors affecting home range of P. blainvillii.—While tracking lizards we infrequently saw

individuals interact with one another. However, on 10 June 2010 we observed two males

interact during a 40 min period where each lizard intermittently displaying a tail-up posture, rocking slowly back and forth, giving quick head-bobs, and slowly following each other. During the same period we were observing the males, a female whose range coincided with the two males remained motionless under a shrub approximately 10 m away, and then moved north when the two males ran south. This male-male interaction is similar to observations made by

Tollestrup (1981) of a nearby population of P. blainvillii. The social behavior of horned lizards is poorly documented, and it is unclear if these types of displays serve a particular purpose such as territory defense, social hierarchy defense, or mate defense (Lynn 1965; Tollestrup 1981;

Sherbrooke 2003). Typical behavior of iguanid males is to spend considerable amounts of time and energy establishing and defending territories through physiological (bright colors) and

behavioral displays (head bobbing, body rocking, tail-up, physical contact). However, it appears that horned lizards are one of the few species of iguanids to lack a rigorous defense of territory or home range and have infrequent displays and social interactions (Stamps 1977; Tollestrup 1981;

Sherbrooke 2003). It is not unusual among horned lizards that there is home range overlap to some degree (Munger 1984; Fair and Henke 1999; Wone and Beauchamp 2003). The home range of the two interacting males we observed overlapped nearly 100%. Considering the time of year (late in the mating season), the almost complete home range overlap, and that horned lizards are generally non-territorial, we speculate that the male-male interaction we observed was perhaps a low level display of mate defense rather than a display of territorial defense.

When above ground and active, P. blainvillii at our sites selected proportionately more areas of bare ground and sparse herbaceous vegetation and avoided areas of dense vegetation, particularly of non-native grasses. These findings are consistent with what has been reported for

P. blainvillii in southern California (Hager and Brattstrom 1997) and in the northern San Joaquin

Valley (Gerson 2011) as well as in other horned lizard species (Whiting et al. 1993; Fair and

Henke 1997; Montgomery and Mackessy 2003). Considering the dorso-ventrally flattened body shape and short legs of horned lizards, this type of microhabitat likely impedes movement. In a study on a closely related species, P. platyrhinos, Newbold (2005) found a significant negative association between Cheatgrass cover and lizard mobility as well as lizard abundance. Harvester ants (Pogonomyrmex spp.), the main prey of horned lizards, are granivores and forage on grass seeds in areas of sparse vegetation (Whiting et al. 1993), where the sit-and-wait foraging strategy of horned lizards would be more compatible with open spaces than with dense vegetation. Much of the early observations of habitat use by P. blainvillii had been obtained by chance encounters or systematic searches (Smith 1946; Tollestrup 1981; Hager and Brattstrom 1997; Gerson 2011).

Because of their cryptic nature and tendency to remain motionless when approached, this presents the problem of bias in that P. blainvillii is generally seen only when they are out in the open and have decided to flee. Concerns have been raised about the accuracy of reporting open areas and sparse herbaceous vegetation as being the preferred microhabitat of horned lizards due to observer bias and increased sightability in this habitat (Fair and Henke 1999; Burrow et al.

2001). However, our study had the advantage of eliminating this bias using telemetry and finding the lizards regardless of sightability, thus providing a more accurate picture as to how they use habitat.

Habitat use at the two sites differed in that the lizards at the Semitropic site were found under a shrub almost as often as on bare ground, whereas the lizards at the Atwell site were found most often on bare ground as well, but followed distantly by areas of sparse vegetation, and then under a shrub. The two sites had different habitat characteristics that could explain the difference in habitat use. In the pasture at the Atwell site, the lizards were often located in large areas of bare ground with little shrub cover, despite the presence of dense patches of shrubs nearby. The pasture also had a higher density of Heermann's Kangaroo Rat burrows. In contrast, the Semitropic site had a greater number of shrubs, compacted soil and fewer rodent burrows. If the lizards are using shrubs primarily for thermoregulation or predator avoidance, as they are known to do (Heath 1965; Hager and Brattstrom 1997; Hult and Germano, unpubl. data), then we should see P. blainvillii using shrubs more often at the Semitropic site. Similarly, we would expect to see lizards using rodent burrows more often than shrubs at the Atwell site.

Interestingly, at the Atwell site we rarely saw them use shrub cover as heat refugia even though shrubs were plentiful. Instead, at high surface temperatures, we found them more often in a rodent burrow (Hult and Germano, unpubl. data). Wone and Beauchamp (2003) also observed

42 burrow-seeking behavior to escape the midday heat in P. mcallii in the south-central tip of

California near the Mexican border. However, we did observe the lizards using shrubs more often than burrows in instances when we approached close enough to prompt them to flee rather than remain motionless. We postulate that the lizards at Atwell could be using shrubs more for predator avoidance than heat relief, while the lizards at the Semitropic site use shrub cover equally for both purposes.

Conservation of P. blainvillii.—The results from our study allow us to make some preliminary recommendations regarding the conservation of horned lizards. The 10 lizards included in our analysis maintained an average home range size of 5.0 ha, but there was large variation from a minimum of 0.58 ha to nearly 14 ha. Because our sample size of observation points was small in some of our home range analysis, our results should be considered a minimum home range and that horned lizards most likely use at least a slightly larger home range than the data shows.

There is small to total overlap between home ranges of individuals. As a result, for a population of 20 lizards who maintain a minimum home range of 5 ha, for example, an area of 100 ha might be needed. Of course, there are other factors that make a home range optimal for any animal other than just size. These factors include prey availability, mates, and microhabitat components critical for predator avoidance, thermoregulation, and shelter. For example, bare ground is an above ground habitat that is favored by these lizards, and sparse vegetation and shrub cover are used more often than expected. Therefore, land containing these microhabitat components have conservation value for lizard populations and should be maintained. We recommend further long-term telemetry studies on P. blainvillii in the San Joaquin Valley to enhance our data, especially over changing seasons and climate. This information becomes more important to land

managers who are interested in the conservation of P. blainvillii as the pressures of human

habitation, especially in the form of habitat loss, continues in the San Joaquin Valley.

Acknowledgements.—We would like to thank Teresa O’Keefe, Natalie Montague, Jeff Bittner,

Peter DeWitt, Denis Kearns, Joaquin Martinez, Miguel Perez, Erin Tennant, and Mona Verma

who assisted us in the field. Without them, this study would not have as much telemetry data as

it does. We are indebted to Jack Mitchell and Steve Laymon who provided valuable information

on Atwell and to Denis Kearns for clarifying botanical terminology. We are grateful to the

Center for Natural Lands Management and Greg Warrick, manager of the Semitropic Ridge

Preserve, for allowing us to conduct our study on their land. We would also like to acknowledge

Sue Lynch, DVM, who provided advice on the use of adhesive when attaching the transmitters and repairing the needle hole to ensure minimal risk of toxicity to the lizards. We very much appreciate Kerry Arroues, Natural Resources Conservation Service (NRCS) supervisory soil scientist, who took the time to come to Atwell to clarify the true boundary of the Sandridge soil series at location 2. This study would not have been possible without the Bureau of Land

Management’s (BLM) Student Career Experience Program and without the support of BLM supervisors Steve Larson and John Skibinski as well as many BLM colleagues. We thank Steve

Laymon and Brandon Pratt for reading an earlier version of this manuscript. All work was carried out under the California Fish and Game Scientific Permit SC-10049 and with the approval of the California State University, Bakersfield Institutional Animal Care and Use

Committee.

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Table 1. Radio-telemetry data for 14 Phrynosoma blainvillii at the Atwell Island and Semitropic Ridge Preserve sites in 2010 in the southern San Joaquin Valley, California. Information includes sex, date of capture, date of last relocation, number of days followed, total number of observations, and the reason (outcome) of the termination of study for each lizard. Date of first Date of last Days Total No. Lizard ID Sex Capture date relocation relocation Followed observations Outcome

Atwell A165.044f F 8-Apr-10 10-Apr-10 1-Jun-10 52 20 Transmitter found on ground A164.144f F 13-Apr-10 15-Apr-10 23-May-10 38 11 Transmitter found on ground A164.127f F 17-Apr-10 23-Apr-10 17-Jun-10 55 30 Lost signal A164.486f F 2-May-10 5-May-10 10-May-10 5 3 Deceased A164.423m M 27-May-10 29-May-10 18-Aug-10 81 62 Shed transmitter A165.024f F 7-Jun-10 8-Jun-10 7-Sep-10 91 64 Shed transmitter A164.425m M 10-Jun-10 11-Jun-10 2-Jul-10 22 19 Lost signal Semitropic S165.224m M 7-Apr-10 10-Apr-10 12-Aug-10 124 60 Lost signal S164.223m M 9-Apr-10 13-Apr-10 22-Jul-10 100 62 Shed transmitter S164.202m M 16-Apr-10 30-Apr-10 9-Aug-10 102 69 Lost signal S164.243f F 23-Apr-10 30-Apr-10 9-May-10 9 5 Transmitter found on ground S165.484f F 23-Apr-10 30-Apr-10 16-Jun-10 47 22 Deceased S165.085m M 4-May-10 9-May-10 13-Jul-10 58 45 Shed transmitter S164.063f F 20-May-10 25-May-10 17-Jun-10 23 6 Deceased

Table 2. Home range estimates of 10 Phrynosoma blainvillii based on 100% minimum convex polygon (MCP) and Fixed-K Local Convex Hull (LoCoH) at the 100% isopleth level at the

Atwell Island and Semitropic Ridge Preserve sites in 2010 in the southern San Joaquin Valley,

California. Information includes sex of the lizard, number of observations used in analysis (n), and the k-value for the LoCoH analysis.

Fixed-K LoCoH MCP

100% Isopleth (ha) 100% Lizard ID Sex n k-value (ha)

Atwell 164.127f F 30 10 0.59 0.87 165.044f F 20 13 1.21 1.24 165.024f F 64 15 2.96 3.09 165.425m M 19 10 3.91 3.95 164.423m M 62 15 3.99 4.24

Total Mean - - 2.53 2.68

(SE) (0.69) (0.69) Semitropic 165.085m M 45 10 0.55 0.58 165.484f F 22 8 1.27 1.30 165.224m M 60 12 7.46 8.39 164.223m M 62 17 11.84 12.18 164.202m M 69 14 13.41 13.93

Total Mean - - 6.91 7.28

(SE) (2.64) (2.74)

Figure 1. Map of the Atwell Island and Semitropic study sites of P. blainvillii in the southern

San Joaquin Valley, California, USA.

Figure 2. Adult Phrynosoma blainvillii showing the transmitter attached to the dorsal side of the lizard. A mesh harness was used to help secure the transmitter attachment. The harness did not provide extra security for transmitter attachment as intended, and we eventually discarded its use. (Photographed by Susan Hult).

Figure 3. Home range as determined by the 100% Minimum Convex Polygon (MCP) method of five Phrynosoma blainvillii at two locations on the Atwell Island site, Kings County, California in 2010. Each lizard's home range is labeled with their identification number followed by f for female and m for male. The yellow outlines delineate the boundary of the two different study locations at the Atwell site.

Figure 4. Home range of five Phrynosoma blainvillii at the Semitropic Ridge Preserve site in

Kern County, California in 2010 as determined by the 100% Minimum Convex Polygon (MCP) method. Each lizard home range is labeled with their identification number followed by f for female and m for male.

50 Atwell 45 40 35 30 25 20 15

Number Observations of Number 10 5 0 Bare Sparse Medium Dense Shrub

100

Semitropic 90 80 70 60 50 40 30 20

Number Observations of Number 10 0 Bare Sparse Medium Dense Shrub

Habitat Type

Figure 5. Frequency of sightings of Phrynosoma blainvillii when above ground in five habitats at the Atwell and Semitropic sites in the southern San Joaquin Valley, California in 2010. The habitat types are bare ground, sparse vegetation, medium-dense vegetation, dense vegetation, and shrub.

100

60 Males Females 50

30 Percentage of LocationsPercentage 20

0 Bare Sparse Medium Dense Shrub

Figure 6. Frequency of sightings of male and female Phrynosoma blainvillii when above ground in five habitats at Atwell and Semitropic study sites in 2010 in the southern San Joaquin Valley,

California.

DEMOGRAPHICS, MORPHOLOGY, THERMOBIOLOGY, AND HABITAT PREFERENCE OF A

POPULATION OF BLAINVILLE'S HORNED LIZARD IN THE SOUTHERN SAN JOAQUIN VALLEY,

CALIFORNIA

1 SUSAN M. HULT AND DAVID J. GERMANO

Department of Biology, California State University, Bakersfield, California 93311

Present address of SMH: 7356 394th Street, North Branch, Minnesota 55056

1Correspondent email: [email protected]

Abstract.—The Blainville's Horned Lizard (Phrynosoma blainvillii) is in decline throughout

much of their range including the San Joaquin Valley of California, USA, which has

undergone significant habitat changes because of human activities. Understanding

patterns of local distribution, vital habitat requirements, and activity levels related to

climatic patterns will be required input for monitoring programs and habitat conservation

and restoration programs. We initiated a two-year baseline study beginning April 2009 in

the southern San Joaquin Valley near Alpaugh, California. In adult P. blainvillii, we

recorded a moderately skewed sex ratio of more males than females, but in young P.

blainvillii, there were more females than males. Average snout-vent length (SVL) of females was 72.31 mm and for males 68.81 mm. The adult horned lizards were most active in April and May while young horned lizards were most active in August and September.

Daily aboveground peak activity times changed with the seasons. In the spring, the morning activity hours peaked at 0900–1100, in summer, it was 0900–1000 and in fall, it was 0900–1300. All age classes of P. blainvillii were most often above ground and active at

surface temperatures of 28–34°C. The presence of alkali flats and sandy soil correlates

with a high abundance of horned lizards, and within our two study locations, they revealed

a distinct preference for Sandridge loamy fine sand over other available soil types. The

lizards used kangaroo rat burrows rather than shrubs for heat refugia but used shrubs

frequently as an escape from predators.

Key Words.—activity patterns, Blainville's Horned Lizard, conservation, demographics,

Phrynosoma blainvillii.

INTRODUCTION

Habitat preference, activity patterns, and demographics are important biological characteristics

for any animal species, and obtaining information on these characteristics is vital to

understanding the ecological role of the species. This type of information is lacking in many

animal species due to their elusiveness, small population numbers, inaccessible habitats, or

camouflage that make them difficult to observe. Thus, we know less about basic biological

characteristics of cryptic species such as horned lizards (Phrynosoma spp.), which rely on their superior ability to blend into their environment and tendency to remain motionless rather than flee, than we know about the same characteristics for more conspicuous species.

This lack of knowledge is especially problematic for the Blainville’s Horned Lizard (P.

blainvillii), formerly known as Coast Horned Lizard (P. coronatum or P. coronatum frontale),

because populations have experienced severe declines throughout their range leaving some

locales of formerly abundant populations nearly or completely absent of lizards (Goldberg 1983;

Jennings 1987; Jennings and Hayes 1994; Fisher et al. 2002; Stebbins 2003). Their historic range extends as far north as the edges of the Sacramento Valley in Butte County, California, south to the northwestern tip of the Pacific coast of Baja California, west along the coast to the

San Francisco Bay, and as far east as the western side of the Sierra Nevada mountains and deserts in southern California (Stebbins 2003; Leaché et. al 2009). Phrynosoma blainvillii are found in a variety of habitats such as semiarid mountains, chaparral, oak woodland, coniferous forest, foothills, and valleys ranging in elevations from sea level to about 1800 m (Smith 1946;

Sherbrooke 2003; Stebbins 2003; Leaché et al. 2009).

Despite their ability to reside in a variety of habitats, P. blainvillii face a number of factors that are contributing to their population declines. Off-highway vehicle use, fires, and livestock grazing may contribute to habitat degradation, although in the San Joaquin Valley where non- native herbaceous plants sometimes attain high densities, these activities may be beneficial by reducing cover (Germano et al. 2001, 2012). Pesticide use in conjunction with residential and agricultural activities decreases the number of native harvester ants (Pogonomyrmex and Messor spp; Pimentel 1995), the preferred prey of horned lizards (Sherbrooke 2003; Stebbins 2003).

The conversion of native habitat to vast tracts of agricultural and industrial commodities leading to outright habitat loss has had the greatest impacts leading to the decline of P. blainvillii populations (Goldberg 1983; Jennings 1987; Jennings and Hayes 1994; Stebbins 2003; Audsley et al. 2006).

Besides outright habitat loss, human population size and continued growth can increase the number of roads, increase recreational use of remote areas that contain optimal lizard habitat, and puts human habitations adjacent to lizards. Urbanization can result in the introduction or expansion of horned lizard predators, such as domestic pets, that can become more common in

60 developed areas (Jennings 1987; Stebbins 2003). Urbanization also results in an increase in habitat fragmentation. Habitat fragmentation is problematic in that it can facilitate the colonization and spread of exotic species in remaining suitable lizard habitat (Suarez et al. 1998).

One of the most vexing exotic species for horned lizards is the Argentine Ant (Linepithema humile; Jennings and Hayes 1994; Fisher et al. 2002; Suarez and Case 2002). Argentine Ants are commonly found in disturbed areas, especially around urban development (Knight and Rust

1990) and fragmented habitats where they are most abundant along edges (Suarez et al. 1998).

Upon establishment of a colony, Argentine Ants proceed to eliminate adjacent native ant colonies (Erickson 1971; Suarez et al. 1998; Suarez and Case 2002). Because horned lizards have a specialized myrmecophagous diet consisting mainly of native harvester ants in adults and smaller native ant species in young, they are vulnerable to habitat changes that result in the loss of native ant species. Argentine Ants are not suitable replacement prey; horned lizards avoid them and turn to arthropods instead, reducing growth (Fisher et al. 2002).

Unlike other Phrynosoma species, particularly the Texas Horned Lizard, P. cornutum, there have been few studies published on the general ecology of P. blainvillii (Smith 1943; Milne and

Milne 1950; Jennings and Hayes 1994). Most studies on P. blainvillii have been on populations that occur in the southern portion of their range (Goldberg 1983; Hager and Brattstrom 1997;

Suarez et al. 1998; Fisher et al. 2002; Montanucci 2004), with one behavioral (Tollestrup 1981) and one ecological (Gerson 2011) study in the San Joaquin Valley. In some lizard species, life- history characteristics can vary widely across their range (Adolph and Porter 1993). The range of P. blainvillii extends across a long portion of west and central California and the northwest tip of Baja California and includes a wide variety of habitats and climatic conditions that could account for different life-history characteristics for P. blainvillii. Localized demographic and

61 ecological data for P. blainvillii from the San Joaquin Valley likely will help clarify conservation needs for this species.

Our research assessed the natural history of P. blainvillii in the southern San Joaquin Valley by focusing on population structure, activity patterns, and habitat preference in a previously under- studied portion of their range. Because horned lizards are ectothermic, their body temperature is essentially determined by air and substrate temperatures. One of the principal means in which horned lizards maintain the required body temperature for given activities is to thermoregulate by modifying their daily and seasonal activity patterns (Smith 1946; Heath 1965; Sherbrooke

2003; Stebbins 2003). Activity patterns are an important characteristic of horned lizard behavior and ecology that can reveal how the lizards relate to their surrounding environment. Therefore, information on activity patterns can be essential to land managers in making decisions on land use and conservation practices within P. blainvillii habitat. Furthermore, knowledge of habitat preference can help predict presence or absence of P. blainvillii in the southern San Joaquin

Valley and aid land managers in acquiring, maintaining, or restoring critical habitat.

MATERIALS AND METHODS

Study sites.—We conducted research in the Tulare Basin in the southern third of the San

Joaquin Valley of California, in southwestern Tulare and southeastern Kings counties, 1.6 km south of the town of Alpaugh (Fig. 2). Much of the San Joaquin Valley is a desert with a

Mediterranean climate of hot, dry summers and cool, moist winters (Germano et al. 2011). July is the warmest and driest month with an average high temperature of 37.8° C while January is the coolest month with an average high temperature of 13.8° C (Western Regional Climate

Center. 2012. Cooperative climatological data summaries. NOAA cooperative stations-

temperature and precipitations. C. California and S. California. Available from http://www.wrcc.dri.edu/climatedata/climsum [Accessed 10 September 2012]). Most of the

average annual rainfall of 183 mm falls December through March (Western Regional Climate

Center. 2012 op. cit.). We chose two study locations on the Atwell Island Project administered

by the Bureau of Land Management.

At Location 1, referred to as "the pasture," we surveyed for lizards in a fenced 156 ha parcel

that had been seasonally grazed by cattle for many years. Within the pasture, there were five soil

series and their associated habitat series (Fig. 2; Table 1). Westcamp loam, Westcamp silt loam,

and Excelsior fine sandy loam comprised approximately 47% of total area and supports the

Seepweed Series habitat (Sawyer and Keeler-Wolf 1997; Soil Survey Staff, Natural Resources

Conservation Service, United States Department of Agriculture. Web Soil Survey. 2009.

Available from http://websoilsurvey.nrcs.usda.gov. [Accessed 10 September 2009]). The dominant shrubs in this area were Bush Seepweed (Suaeda moquinii) and Alkali Heath

(Frankenia salina), while Saltgrass (Distichlis spicata) and non-native annual grasses (Bromus

spp.) were the dominant grassland species present. Spikeweed (Centromadia pungens) and

Goldfields (Lasthenia californica and L. minor) were the dominant (Table 1). The Sandridge

loamy fine sand and Posochanet silt loam, which comprised approximately 53% of the total area,

supports the California Annual Grassland habitat series (Sawyer and Keeler-Wolf 1997; Soil

Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture.

2009. op. cit.). A mixture of non-native and native annual grasses typically dominates this habitat series (Sawyer and Keeler-Wolf 1997). However, cattle grazing occurred throughout the pasture and the dominant vegetative structure were the shrubs Goldenbush (Isocoma acradenia)

with a few Valley Saltbush (Atriplex polycarpa), and the forbs Fiddleneck (Amsinkia menziesii),

Broadleaf Filaree (Erodium botrys), and Spikeweed (Centromadia pungens). Non-native annual

grasses (e.g., Bromus spp.) were present, but were generally grazed or trampled down.

Throughout the pasture, there were many large open spaces with little or no vegetative structure

due to cattle grazing, the natural senescence of herbaceous vegetation as the season became

hotter and drier, and an abundance of soil mounds created mostly by Heermann's (Dipodomys

heermanni) kangaroo rats. Sympatric lizards in the pasture included the California Whiptail

(Aspidoscelis tigris munda) and Western Side-blotched Lizard (Uta stansburiana elegans). The overall topography was mostly level at an elevation range of 61–66 m above sea level. The land surrounding the pasture was formerly cultivated fields that were fallow or had undergone habitat restoration treatments in the years preceding our study. Unlike the immediately surrounding areas, the pasture had not undergone significant substrate disturbance such as canal or road development, deep disk plowing, or laser leveling, which is exactly the type of habitat most in need of study and preservation that Jennings and Hayes (1994) stressed was so important in the conservation of this species. Based on visual estimates and aerial imagery, the overall habitat within the pasture was 30% dense herbaceous vegetation, 25% bare ground, 20% shrubs, 15% sparse herbaceous vegetation, and 10% medium dense herbaceous vegetation. The management practice at the time of our study was continuous seasonal cattle grazing.

The second location (Location 2) was a 120 ha area adjacent to and southwest of the pasture, but separated by an unlined irrigation (Poso) canal (Fig.2). This area was not fenced in and we delineated the boundary based on soil type, vegetative communities, roads, and reports of historical horned lizard sightings. This location had been cultivated with grain crops until the late 1980s and had been fallow since that time. Despite the agricultural activity, Location 2 had

also never undergone laser leveling or deep disk plowing (USDI unpubl. report 2010). There

was never a grazing regime at this location with the exception of an occasional sheep trespass.

The soil types and associated vegetative communities were similar to the pasture (Table 2).

However, because of the decades of inactivity, all of the soil series and associated vegetative

communities in Location 2 were dominated by dense areas of non-native annual grasses (Bromus

spp.) with fewer scattered patches of shrubs and forbs. An unpaved and rarely used road

bisected Location 2 and this was the main source of open space and bare ground. Aside from the

road, a few rodent burrows scattered throughout the location provided areas of bare ground and

sparse herbaceous vegetation. There were narrow trails formed by Desert Cottontails (Sylvilagus

auduboni), Black-tailed Jackrabbits (Lepus californicus), and Heermann's Kangaroo Rats in the

dense grass. The Western Side-blotched Lizard and the California Whiptail were the only other

lizard species we observed at this location. Based on visual estimates and aerial imagery, the

overall habitat in this location as 80% dense grassland, 10% bare ground, 5% shrubs, 5%

medium dense herbaceous vegetation, and < 5% sparse herbaceous vegetation.

Field data collection.—We conducted our research over two seasons beginning 20 April 2009 and continued through 15 November 2010. In the first season, we focused our search times between 0800–1500 to coincide with peak activity of the first half of the day to optimize our chances of seeing lizards and obtaining maximum demographic and morphometric data. In the second season, 2010, we increased our search times to include more afternoon and evening encounters to determine additional periods of lizard activity beyond peak periods.

We located lizards using meandering transects and chance encounters 5–6 days a week.

Meandering transects were accomplished by walking linear pathways within the entire boundary

65 of both locations using various landmarks arbitrarily chosen as end points, such as a utility pole or fence posts. We made searches during all weather conditions except for rainfall, which made the dirt roads leading to our study site impassible. We captured lizards by hand and recorded the date, time of day, and the capture location using Global Positioning System (GPS) in the WGS

1984 coordinate system obtained by a Magellan MobileMapper CX GPS Unit (Magellan, Santa

Clara, California, USA). We recorded the air temperature at chest height and wind speed using a

Kestrel 3000 series pocket weather meter (Nielsen-Kellerman, Boothwyn, Pennsylvania, USA).

We measured surface temperature by propping a Max/Min digital thermometer (Forestry

Suppliers, Inc., Jackson, Mississippi, USA) approximately 2 cm off the surface and shading it from direct sunlight with our bodies. Once we finished data collection, we returned each lizard to its exact capture location. We designated the seasons to have spring include the months of

April and May, summer include the months of June, July, and August, and fall to include the months of September, October, and November.

Demography and morphometrics.—We recorded snout-vent length (SVL) and tail length (TL) to the nearest 1 mm and mass to nearest 1 g using a 10 g or 60 g spring scale (PESOLA, Baar,

Switzerland). We determined the sex of the lizard based on the presence of enlarged post-anal scales that are indicative of males. To give lizards > 55 g a unique identification, we inserted a

12 mm Passive Integrated Transponder (PIT) tag (Biomark Inc., Boise, Idaho) that we injected subcutaneously on the left margin of the ventral side using a 12-guage needle. We closed the small hole left by the needle by gently pinching the margin of the hole together and then applying a drop of cyanoacrylate glue.

We recorded the age class for each lizard as either adult or young. We used a combination of factors in distinguishing adult lizards from young lizards, such as the time of year they were found (most adults are active predominantly in the spring and early summer; Howard 1974;

Pianka and Parker 1975; Hager and Brattstrom 1997), snout-to-vent (SVL) length, and reproductive condition. Previous studies have used a broad range of minimum SVL, from 61–75 mm, to classify P. blainvillii as adults (Howard 1974; Pianka and Parker 1975; Hager and

Brattstrom 1997; Gerson 2011). A dissected specimen from southern California was sexually mature at 61 mm SVL (Howard 1974) and a female closer to our study site had eggs at 65 mm

SVL (Gerson 2011). Based on all of these factors, we classified lizards ≥ 63 mm SVL as adults.

Unlike minimum adult SVL size, there is more consensus as to the size of hatchlings: 24–31 mm

(Shaw 1952; Howard 1974; Hager 1992).

Activity.—At the time of each lizard encounter, we recorded time of day, surface temperature, soil temperature, and ambient air temperature. We classified the activity level of each lizard upon each encounter as either active, meaning fully exposed and eating, mating, or sunning; or in shade, meaning we detected the lizard under shrubs or in patches of herbaceous vegetation. In

2009, we based activity levels on locating lizards by chance encounters during our meandering transect surveys. This type of sampling done on an extremely cryptic species such as P. blainvillii inherently involves observer bias based on visibility and our ability to spot them. As a result, we categorized activity levels as either 'active' or 'seeking shade.' However, we used radio-telemetry in 2010 for a home range study (Hult and Germano, unpubl. data), which allowed us to locate seven individual lizards regardless of visibility. We used the data from the

155 observations we recorded for these seven lizards as a supplement to either confirm or refute our observations of activity levels from the 2009 season.

Habitat assessment.—At the time of a lizard encounter, we noted the soil type as simply loose or compact as well as its color. We more accurately defined the soil type by mapping the GPS coordinates of every lizard location into the ArcMap function of ArcGIS v. 9.3.1 software

(Environmental Systems Research Institute, Inc., Redlands, California). We used a USDA soil series map (Soil Survey Staff, Natural Resources Conservation Service, United States

Department of Agriculture. 2010. op. cit.) as a base layer (Fig 2). This enabled us to record the true soil series for each location. The soil series map had delineated boundaries that enabled us to calculate the area that each soil series covered within the boundaries of our two study locations. Unlike the soil series, we did not have a habitat series layer in ArcGIS that would have allowed us to calculate the area of the habitat series within the two locations. However, our field knowledge of the location sites as well as aerial photographs revealed that the habitat series associated with a particular soil series virtually matched the boundaries of the soil series. In this way, we were able to calculate the area of the habitat series occupied within the boundary of our two study locations.

Statistical analysis.—We compared average SVL of males to females using ANOVA.

Because the data on mass did not have equal variances, we compared the mass of males to females using the Mann-Whitney test. We used Chi-square with Yates correction to compare sex ratios of adults and young. We compared size distributions from 2009 to 2010 using the

Kolmogorov-Smirnov test by categorizing lizards by 5 mm SVL increments from 25–90 mm

SVL. To determine if adult and young lizards have significantly different sex ratios between

years or in both years combined, we used the Chi-square goodness of fit test for observed counts.

We compared hourly activity times of lizards we found in the morning of spring, summer, and

fall using a Fisher's exact test. We did the same for activity periods associated with surface

temperatures. To determine if young lizards remain active at higher or lower surface

temperatures, we compared the activity periods of young and adult lizards against surface

temperatures using a Kolmogorov-Smirnov test. We performed the same tests separately on the

data from our telemetered lizards to provide an unbiased affirmation or refutation of the results

from our observations on non-telemetered lizards.

To determine if P. blainvillii was found on a particular soil series and associated habitat series

differently than equal use, we used a Chi-square goodness of fit test. To see if P. blainvillii used a particular soil type and associated habitat series differently than random use, we compared the same field data to a set of 100 randomly located coordinates within the pasture. To generate 100

random coordinates, we used Hawth’s Analysis Tools for ArcGIS v. 3.27 (Beyer 2004). We

then uploaded the coordinates into a Magellan GPS unit, which we used to navigate to each

point. At each random point, we mimicked the data collection methodology that we employed

when we encountered a lizard and recorded the same data. We analyzed our random and field

data using a contingency table test. We ran a separate analysis on the 155 observations from our

seven telemetered (2010) lizards using a contingency table and compared it to our 2009 data.

For all tests, α = 0.05.

RESULTS

Demography and morphometrics.—In 2009 we encountered 146 lizards and of those, 131

were unique individuals (Table 2). Of those unique individuals, 30.3% (n = 40) were adults with

a sex ratio 1:1.2 females to males (55% males; n = 22), although the ratio was not significantly

different from 1:1 (χ2 = 0.225, df = 1, P = 0.635). The young lizards of that year exhibited a

significantly skewed (χ2 = 4.396, df = 1, P = 0.036) female (n = 56) to male (n = 35) sex ratio of

1:0.57. In 2010, we encountered 112 lizards with 107 of those being unique individuals (Table

2). We had four young lizards for which we could not determine sex. Adults comprised 23.4%

(n = 25) of the total individual lizards with a female to male sex ratio of 1:1.3 (56% males; n =

14), and the ratio was not significantly different from 1:1 (χ2 = 0.160, df = 1, P = 0.689). In

2010, though, the sex ratio of young lizards was not skewed to either sex as we found equal numbers of females and males (n = 39 each sex). The average adult female SVL was 72.31 mm

(± 5.6 SD) and weighed an average 24.20 g, while the average adult male SVL was 68.81 mm (±

4.1 SD) and weighed an average of 20.31 g. Average adult female SVL was larger than that of adult males (F1,63 = 8.50, P = 0.005), as was mass (W = 1186.5, P = 0.001). The smallest SVL

of all lizards encountered was 26 mm and the largest SVL was 85 mm.

Activity.—We encountered P. blainvillii at our study site 5 April - 11 November across the two

years. The highest level of above ground activity exhibited by adults occurred from late April

and May, with a sharp decrease in activity beginning in June and lasting throughout the season

(Fig 3). Juveniles and hatchlings were most active in August and September. Hatchlings (25–31

mm SVL) began to appear in July and we continued to find them into early November,

suggesting eggs were being laid from April until early September based upon a 60-day

incubation period (Howard 1974; Zeiner et al. 1988; Jennings and Hayes 1994). By the middle

of November, we no longer encountered any lizards of any age class.

Peak activity periods differed significantly among the seasons (P < 0.001; Fig. 4). In the

spring, aboveground activity peaked for three hours from 0900–1100. This was significantly

different from summer (P = 0.026) in which peak activity was reduced to two hours from 0900–

1000. In the fall, P. blainvillii's activity peaked for a four-hour period between 0900–1300 and was significantly different from that of summer (P < 0.001) and spring (P < 0.001).

We observed P. blainvillii at surface temperatures ranging from 19–41° C, but they were most

often active at surface temperatures between 28–34° C throughout the year (Fig. 5). The

corresponding average ambient air temperature at chest height during their peak surface

temperature activity was 26–30° C. Adults and juveniles were active at the same range of

surface temperatures throughout the year. The data from the seven lizards (155 observations) we

radio tracked in 2010 corroborated our findings on the surface temperature data and activity

periods we collected in our first year from non-telemetered lizards (Fig. 5). Additionally, the

data from the telemetered lizards revealed that when surface temperatures reached approximately

33° C, lizards began to seek cover in burrows. When surface temperatures were less than

approximately 24° C, lizards tended to bury themselves in sand.

Habitat assessment.—We found P. blainvillii significantly more often than expected on the

Sandridge loamy fine sand soil series and its accompanying vegetative community than any

other soil series based on equal use (χ2 = 471.34, df = 3, P = 0.001; Fig. 2). The same held true

when the lizard data was compared to random point data (χ2 = 121.7, df = 3, P = 0.001).

Although the Sand ridge series comprises approximately 50% of the total soil series in each of

the two locations, 98.2% of our observations occurred there. The lizards that had transmitters on

in 2010 corroborated our findings from the data we collected in our first year from non-

telemetered lizards in that they preferred the Sandridge soil series and associated habitat and

avoided the Westcamp, Posochanet, and Excelsior soil series and their associated habitats (χ2 =

603.92, df = 3, P = 0.001).

DISCUSSION

Horned lizards are atypical among most vertebrates in that for nearly all Phrynosoma species,

females are significantly larger than males (Pianka and Parker 1975; Montgomery and Mackessy

2003; Sherbrooke 2003; Lahti et al. 2010; Gerson 2011). This is what we found for P. blainvillii

on our study site in the San Joaquin Valley. Our average female SVL of 72.3 mm and male SVL

of 68.8 mm appeared to be similar to the average female SVL of 75.1 mm and male SVL of 69.8

mm from another population of P. blainvillii in the San Joaquin Valley in Merced County,

approximately 240 km northwest of our location (Gerson 2011). However, a one-sample t-test revealed the difference to be significant for both males (with one outlier, 82.0 mm, removed) and females. Despite the statistically significant difference, the adult lizards from the San Joaquin

Valley populations were closer in size to each other than either was to a population of adult lizards in southern California, near Moreno Valley, approximately 362 km southwest of our study site. In this population, Hager (1992) reported an average maximum adult male SVL of

91.6 mm and an average maximum adult female SVL of 103.0 mm. The maximum female SVL

72 of 85 mm and 87 mm from the Atwell and Merced county populations, respectively, were considerably smaller than the average maximum SVL of males, let alone the females from southern California (Hager 1992; Gerson 2011). When the lizards of the San Joaquin Valley and the lizards of southern California were considered a separate subspecies, this geographic difference in SVL length had been reported in previous studies as one of the morphologic characteristics that were used to differentiate the populations as P. c. blainvillii in the south and

P. c. coronatum in the north (Smith 1946; Jennings and Hayes 1994). Similar latitudinal differences in adult SVL size have been noted in other Phrynosoma species as well

(Montgomery and Mackessy 2003; Endriss et al. 2007). The tendency of smaller sizes in higher latitudes may be the consequence of shorter seasonal activity period and a reduction in available energy to produce primary productivity, or some other unrecognized factor or combination of factors (Montgomery and Mackessy 2003). Whereas adult SVL sizes at our site differed from other populations of P. blainvillii on a spatial scale, the average hatchling size of 25–31 mm SVL

(Shaw 1952; Howard 1974; Hager 1992; Gerson 2011) is relatively consistent across latitudes and the smallest lizards we found fell in line with that range.

Sex ratios in adult horned lizards do not appear to be consistent. The adult sex ratio from the

P. blainvillii population at our site was nearly 1:1, which is consistent with some findings

(Pianka and Parker 1975; Turner and Medica 1982; Gerson 2011) but not with others who reported a skewed adult sex ratio (Tollestrup 1981; Henke 2003; Montgomery and Mackessy

2003). Phrynosoma blainvillii at our study sites had seasonal activity patterns that closely mimicked the seasonal activity patterns of other P. blainvillii populations. The emergence from winter dormancy in mid-April and continued activity into November is characteristic of this species (Jennings and Hayes 1994; Hager and Brattstrom 1997; Burrow et al. 2001), although the

73 beginning and end of seasonal activity can vary by individual, geographic, and yearly climate variables (Jennings and Hayes 1994; Hager and Brattstrom 1997; pers. obv). The age-class seasonal activity differences we observed are congruent with other populations of P. blainvillii as well. Hager and Brattstrom (1997) found that adults were active from April-July with peak activity in June and mostly not found after July. Hatchlings and young were found from July-

October. This age-class activity pattern was also reported in a closely related species, P. platyrhinos, in Utah (Pianka and Parker 1975) and in P. solare from Arizona (Parker 1971). We found the same pattern for P. blainvillii at our site, with the exception of seeing young lizards into early November.

Horned lizards modify their daily surface activity in response to thermal variations (Smith

1946; Heath 1965; Pianka and Parker 1975; Hager and Brattstrom 1997; Sherbrooke 2003).

Many species, including P. blainvillii, are reported to have a daily unimodal activity pattern in the cooler months of spring and fall. That is, once they begin their daily activity, they remain steadily active throughout the day (Heath 1965; Pianka and Parker 1975; Hager and Brattstrom

1997; Montgomery and Mackessy 2003). In contrast, P. blainvillii at our site did not remain steadily active throughout the morning in the spring and fall; rather, they had periods where activity noticeably peaked for a few hours then dropped off considerably midday. Furthermore, their specific hours of activity shifted with the seasons. In the spring, the lizards were out earlier in the morning and for a shorter period of time than in the fall. While the apparent limited daily activity is atypical of P. blainvillii, the shift in daily activity patterns according to season is consistent with what has been reported previously (Smith 1946; Heath 1965; Pianka and Parker

1975; Hager and Brattstrom 1997). During the hot summer months, surface activity mirrored that of other desert-dwelling species in that they are rarely active at all (Pianka and Parker 1975;

Zimmerman et al. 1994; Hager and Brattstrom 1997; Montgomery and Mackessy 2003). The reason our P. blainvillii maintained peak periods of daily activity even in the cooler months is unclear, but it is not likely due to observer bias since the data collected from the telemetered lizards revealed the same limited hours of daily activity throughout the year, regardless of season.

Because horned lizards are ectotherms, they must maintain optimal body temperatures when active during the day to digest prey most efficiently and to avoid hypothermia and overheating.

They do so behaviorally by basking, burrowing, and seeking the shade of vertical objects or retreating into rodent burrows (Heath 1965). We found that surface temperatures significantly affected the behavioral thermoregulatory pattern of P. blainvillii at our study sites in the San

Joaquin Valley. At surface temperatures of 28–34° C, lizards of all age classes were most active.

Additionally, the data from the telemetered lizards revealed that at surface temperatures approximately 35° C and above, lizards tended to seek cover in a burrow and at surface temperatures 24° C and below, they tended to bury themselves in sand. The proper soils can provide a favorable substrate for horned lizards in which they can excavate nests for egg laying, bury themselves in for thermoregulation, and blend into for predator avoidance. In addition, the proper soils support important resource vegetation for refugia and seed sources for their main prey, harvester ants (Pogonomyrmex spp.). We found lizards almost exclusively in Sandridge loamy fine sand. The texture of this sand is moderately course (Soil Survey Staff, Natural

Resources Conservation Service, United States Department of Agriculture. 2011. op.cit.), which would likely be advantageous to P. blainvillii in that it may be an easy substrate in which to bury for thermoregulation. These soils also may enhance the hatching success of the eggs. Moisture content of the nest site is a critical factor in embryonic development. Eggs that lose too much

75 moisture become desiccated, which can be lethal to the embryo (Muth 1980; Sherbrooke 2003).

In contrast, eggs that are hyper-hydrated risk an increase of fungal infections and reduced gas exchange (Warner and Andrews 2002). Of all the soil types at our study sites, Sandridge has the highest permeability (moderately rapid) and drainage (somewhat excessively well drained) class while Westcamp loam, Posochanet silt loam, Excelsior fine sandy loam have moderately slow to very slow permeability and are moderately well to somewhat poorly drained (Soil Survey Staff,

Natural Resources Conservation Service, United States Department of Agriculture. 2010. op. cit.). The higher permeability and drainage of Sandridge soils allows rainwater to percolate down through the soil, which would allow sufficient moisture for egg development as well as preventing excessive moisture build-up. The same soil characteristics are most likely beneficial for harvester ants, an important food for horned lizards (Smith 1946; Heath 1965; Pianka and

Parker 1975; Montanucci 1989; Suarez and Case 2002; Barrows and Allen 2009). Incidentally, we observed an abundance of harvester ants on Sandridge soil but very few harvester ants in the other soils. Montanucci (1968) described alkali soils and sandy soils as important predictors for

P. blainvillii presence. Alkali soils are those that have a pH ≥ 8.5. Though all the soils in the two study locations have a range of pH that could classify them as alkali soils, the Sandridge soil has the lowest range of pH and salinity. It is also interesting to note that, with the exclusion of the Sandridge and Excelsior fine sandy loam, the other soils at our site have clay and silt components. Clay and silt have lower permeability, finer texture, and support different vegetation than Sandridge. Without further study in this particular area, we can only infer that perhaps soil texture, stability, permeability, and associated habitat may be important factors as to the clear preference of P. blainvillii at our study site for the Sandridge soil series. Our inference

76 is supported by Gerson's (2011) findings in which P. blainvillii may be avoiding areas with a clay soil component and favored those with a sandy loam and loam soils.

Although some quantitative studies of demography, morphometrics, activity patterns, and habitat preference of P. blainvillii in nature exist (Goldberg 1983; Hager and Brattstrom 1997;

Suarez et al. 1998; Fisher et al. 2002; Montanucci 2004), only a few papers have discussed variations of these natural history aspects of P. blainvillii in the San Joaquin Valley (Tollestrup

1981; Gerson 2011). Because P. blainvillii occurs in a variety of habitat types, being knowledgeable of these life-history traits as they pertain to the particular locale of the population of concern is critical. For example, our study revealed differences between peak daily activity times, dates, thermoregulatory behavior, and morphometrics of P. blainvillii in the San Joaquin

Valley and those of P. blainvillii in southern California. Furthermore, the harvester ant species present at our study site did not build conspicuous ant mounds, which previous studies have indicated is an important variable for determining the presence/absence of horned lizards

(Munger 1984: Whiting et. al 1993). Instead, the entrance to harvester ant nests was usually an inconspicuous hole in the ground. We found the presence of P. blainvillii scat, readily identifiable by the presence of ant exoskeletons, was a more reliable indicator of lizard occupancy than the presence of ant mounds.

Our field study suggests that areas consisting of well-drained, sandy loam and alkali soils along with the presence of kangaroo rat burrows, shrubs, and an abundance of harvester ants were likely important habitat characteristics for P. blainvillii at our study locations.

Additionally, our study specifies the dates, times, and temperature ranges in which P. blainvillii in southern San Joaquin Valley are most likely to be above ground and active. This information has several management applications. Land managers can use this information to conduct

77 presence/absence surveys, schedule maintenance and other activities to minimize the impacts on

P. blainvillii, and to educate recreationists such as bikers and off-road vehicle users to the times that P. blainvillii are above ground and in areas of open habitat such as roads and trails.

Considering the human population growth in the Central Valley is predicted to occur at one of the fastest rates of any region in California (California Department of Finance. 2012. Interim population projections for California and its counties 2010-2050. Available from http://www.dof.ca.gov/research/demographic/reports/projections/interim/view. [Accessed 09

September 2012]) habitat destruction, degradation, and fragmentation can reasonably be expected to continue. Field data from the present study provides baseline information on the demographics, habitat preferences, and activity patterns that can help create local land management strategies, evaluation of the impacts of continued surface disturbances, as well as contribute to the larger effort to monitor P. blainvillii population status throughout its range.

Acknowledgments.—We would like to thank Dana Gasper and Teresa O’Keefe for the many hours of field assistance they provided, resulting in large amounts of valuable data for this study.

We would also like to acknowledge Sue Lynch, DVM, who provided advice on the use of adhesive when repairing the hole left by the PIT tag needle to ensure minimal risk of toxicity to the lizards. We very much appreciate Kerry Arroues, Natural Resources Conservation Service

(NRCS) supervisory soil scientist, who took the time to come to Atwell to clarify the true boundary of the Sandridge soil series at location 2. We are grateful to Jack Mitchell and Steve

Laymon who provided valuable information on all things Atwell and to Denis Kearns for giving terminology advice on all things botany. This study would not have been possible without the

Bureau of Land Management’s (BLM) Student Career Experience Program and without the

78 support of BLM supervisors Steve Larson and John Skibinski as well as many BLM colleagues.

We thank Steve Laymon and Brandon Pratt for reading an earlier version of this manuscript. All work was carried out under the California Fish and Game Scientific Permit SC-10049 and with the approval of the California State University, Bakersfield Institutional Animal Care and Use

Committee.

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Table 1. Soil and habitat characteristics of Locations 1and 2 in the southern San Joaquin Valley in Kings and Tulare counties, California, USA. Acronyms are SRLFS = Sandridge loamy fine sand; WL = Westcamp loam; PSL = Posochanet silt loam; EFSL = Excelsior fine sandy loam.

An entry for Westcamp Silt Loam (WSL) for Location 1 and Excelsior sandy loam (ESL) for location 2 were not included because they accounted for < 1% of total area at each site.

SRLFS WL PSL EFSL Location 1

Percentage of Area 53% 34% 7% 7% (approx.) Drainage Class Somewhat Somewhat poorly Moderately well Well drained; moderately excessively drained; very drained; slow slow permeability drained; slow permeability permeability moderately rapid permeability pH 7.6 8.5 8.6 8.5 Associated Habitat California Annual California Annual Seepweed/California Annual Seepweed Series Grassland Grassland Grassland Habitat 40% sparse 30% dense 50% medium- Northern half resembles Characteristics vegetation, vegetation, dense vegetation, Seepweed habitat; southern half resembles California Annual Grassland. 20% bare ground 25% bare ground 20% bare ground, 35% sparse vegetation, 20% shrubs 20% shrubs 20% shrubs, 35% shrubs, 10% dense 15% sparse 10% dense 20% bare ground, vegetation, vegetation, vegetation 10% medium- 10% medium- 10% medium-dense dense vegetation dense vegetation vegetation Associated Shrubs: Shrubs: Shrubs: Shrubs: Herbaceous Species Isocoma Suaeda moquinii, Isocoma Suaeda moquinii, Frankenia acradenia; Frankenia salina; acradenia; salina; Forbs: Forbs: Forbs: Forbs: Amsinkia Centromadia Amsinkia Amsinkia menziesii, menziesii, pungens, menziesii, Centromadia pungens, Centromadia Lasthenia Centromadia Lasthenia californica and L. pungens; californica and L. pungens; minor; minor; Grasses: Grasses: Grasses: Grasses: Non-native Distichlis spicata, Non-native Non-native annual annual non-native annual annual

SRLFS WL PSL EFSL Location 2

Percentage of Area 45% 24% 30% (approx.) -- Drainage Class Somewhat Somewhat poorly Moderately well excessively drained; very slow drained; slow drained; moderately permeability permeability rapid permeability -- pH 7.6 8.5 8.6 -- Associated Habitat California Annual California Annual Seepweed Series Grassland Grassland -- Habitat Vertical structure of Vertical structure Vertical structure Characteristics dense non-native of dense non-native of dense non-native annual grass and annual grass and annual grass and scattered shrubs scattered shrubs scattered shrubs 60% dense 60% dense 80% dense vegetation vegetation vegetation 20% medium-dense 30% shrubs 20% bare ground vegetation 20% bare ground 10% bare ground 10% shrubs 5% shrubs -- Associated Shrubs: Shrubs: Shrubs: Herbaceous Species Isocoma acradenia Suaeda moquinii, Isocoma acradenia Frankenia salina Forbs: Forbs: Forbs: Amsinkia menziesii, Centromadia Amsinkia menziesii, Centromadia pungens Centromadia pungens pungens Grasses: Non- Grasses: Non- Grasses: Non- native annual native annual native annual --

Table 2. Sex, age class, and descriptive statistics of snout-vent length (SVL) and body mass of

Phrynosoma blainvillii captured April–November in 2009 and 2010 in the southern San Joaquin

Valley in Tulare and Kings counties, California USA. Recaptures not included in descriptive statistics.

SVL (mm) Body mass (g) No. Year Age Sex n Recaptures Mean SE Range Mean SE Range

2009 Adult F 19 1 72.3 1.3 63–85 1.3 14.5-32.0

Adult M 26 4 68.8 0.74 63-75 20.3 0.77 15.0-26.5

Young F 62 6 46.5 1.5 29-62 7.5 0.6 1.5-15.0 Young M 39 4 47.7 1.44 31-62 7.7 0.72 2.5-18.5

2010 Adult F 12 1 72.2 1.8 63-81 25 2.2 14.0-38.0

Adult M 17 3 69.1 1.4 63-82 21 0.93 16.5-28.0

Young F 39 0 39.7 1.5 26-61 4.9 0.56 1.4-13.5

Young M 40 1 42.1 1.3 26-57 5.7 0.5 1.0-13.5

Figure 1. Map of the study site, Atwell Island, in Kings County in the San Joaquin Valley,

California, USA.

Figure 2. The two study locations at the Bureau of Land Management's Atwell Island Project in the southern San Joaquin Valley, California, USA, showing the soil series within the study locations. The thick black lines represent the two study location boundaries and the red dots represent the location coordinates of all individual Phrynosoma blainvillii observed over our two-year study.

Figure 3. Frequency distributions of snout-vent lengths of individual Phrynosoma blainvillii captured in April-November 2009 and 2010 at the Atwell Island study sites in the southern San

Joaquin Valley, California, USA. A) April and May. B) June and July. C) September and

November. Data from recaptured lizards was not included in this analysis.

Figure 4. Frequency of sightings of Phrynosoma blainvillii by time of day at the Atwell Island study site in the southern San Joaquin Valley, California, USA. A) April and May B) June and

July. C) September and November.

Figure 5. Frequency of the substrate surface temperatures at which Phrynosoma blainvillii were active at the Atwell Island site in the southern San Joaquin Valley, California, USA. In 2010 we fitted several lizards with radio-transmitters, which allowed us to use telemetry to locate lizards in an unbiased fashion and served as a comparison to lizards found without telemetry.

DIET ANALYSIS OF A POPULATION OF THE BLAINVILLE'S HORNED LIZARD (PHRYNOSOMA

BLAINVILLII) FROM THE SOUTHERN SAN JOAQUIN VALLEY, CALIFORNIA, USA

While conducting field studies on demographics and morphology of Blainville's Horned

Lizards (Phrynosoma blainvillii) in the southern San Joaquin Valley near Alpaugh, California,

USA, I fortuitously collected P. blainvillii fecal pellets (scat) to document prey items present in

the scat and prepare a dietary analysis of this population. Phrynosoma blainvillii are in decline

range wide and is listed as a California Species of Special Concern and a Bureau of Land

Management (BLM) Sensitive Species. Dietary considerations are an important component in

understanding the dynamics of a lizard population with its habitat and with co-existing species

(Duffield and Bull 1998). Horned lizards are one of only a few species that consume primarily

harvester ants (Pogonomyrmex sp.), and the presence of horned lizards is closely tied to the

presence of these ants (Whitford and Bryant 1979; Donaldson et. al 1994; McIntyre 2003). The

dietary inclination of horned lizards can be determined by examining the contents of their fecal

pellets. Horned lizard scat is easily identified from other lizard scat (Fair and Henke 1997;

Suarez et al. 2000; Sherbrooke 2003) by their large, fat, cigar-shaped pellet with a small white plug of uric acid attached at one end and by the presence of the indigestible exoskeletons of their prey, mainly native harvester ants (Fig. 1).

Figure 1. Phrynosoma blainvillii fecal pellet collected from a population in the southern San Joaquin Valley, California. Harvester ant (Pogonomyrmex sp.) exoskeletons are visible.

The primarily myrmecophagous diet of horned lizards distinguishes them from almost all other North American lizard species (Milne and Milne 1950; Pianka and Parker 1975;

Sherbrooke 2003). Within the genus, however, not all species are equivalent in their degree of myrmecophagy. For example, P. solare and P. platyrhinos have a diet of approximately 90% ants, while P. hernandesi and P. blainvillii are among those with the lowest degree of myrmecophagy, approximately 60% (Pianka and Parker 1975; Sherbrooke 2003). Other prey items consumed by horned lizards include beetles, flies, grasshoppers, spiders, and other arthropods (Milne and Milne 1950; Pianka and Parker 1975; Montanucci 1989; Sherbrooke

2003). Horned lizards have been known also to consume soft-bodied arthropods when available

(Milne and Milne 1950; Pianka and Parker 1975). Because of the non-invasive nature of my dietary study, I could only identify prey items whose identifiable features survived the digestive

94 tract of lizards, thus introducing a bias toward hard-bodied arthropods. For example, darkling beetles (Tenebrionidae) were abundant at my study site and I found adult stage elytra in the lizard scat. Larval-stage darkling beetles were likely abundant as well and it is possible that horned lizards ate them, but their soft bodies did not survive the digestive tract and thus were not apparent in scat.

I collected 92 fecal pellets beginning 20 April and continued through 15 November

2009. I dried them overnight in a 79.4 °C oven to eliminate fungal growth and water content. I took an initial weight of the pellet and under a microscope; I removed sand, detritus, and the uric acid plug leaving behind only exoskeletons. I re-weighed these remains. I sorted the prey items into either ants (Formicidae), beetles (Coleoptera), or other/unknown arthropods. Of the ant species found in the scat, only Pogonomyrmex sp. was readily identifiable to genus. I was able to identify remains as Coleoptera because nearly all of the forewings (elytra) were fused and survived the digestive tract intact, making them easily identifiable as adult stage beetles.

I found that nearly all scat contained ants (Fig. 2), particularly Pogonomyrmex sp.

Furthermore, 67% of scat contained Coleoptera as well. I also found that compositionally, more fecal pellets contained ants and beetles rather than exclusively ants (Fig. 3), suggesting that beetles, in addition to ants, were an important component of P. blainvillii diet. Furthermore, arthropods other than ants and beetles were consumed to a small extent (Fig. 2). These findings are consistent with the literature on P. blainvillii diet that although ants, particularly native harvester ants, are their primary prey items, beetles may be consumed to a large extent and occasionally dominate their diet, and that other arthropods may be consumed but to a smaller extent (Milne and Milne 1950; Pianka and Parker 1975; Sherbrooke 2003).

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20 Percentage of of Scat Percentage

0 90 62 13 Ants Beetles Other Arthropods

Figure 2. Percentage of scat that contained ants, beetles, and other unidentified arthropods found in 92 fecal pellets collected from a population of Phrynosoma blainvillii in the southern San Joaquin Valley, California. The number above the name of the prey items indicates the actual number of pellets in which each prey item was found.

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20 Percentage of of Scat Percentage 0 13 62 28 2 0 All 3 Prey Ants+Beetles Ants Only Beetles Only Other Only Items

Figure 3. Composition of prey items found in 92 fecal pellets collected from a population of Phrynosoma blainvillii in the southern San Joaquin Valley, California. The number above the categories indicates the actual number of pellets in which each prey item was found.

LITERATURE CITED

Donaldson, W., A.H. Price, and J. Morse. 1994. The current status and future prospects of the

Texas Horned Lizard (Phrynosoma cornutum) in Texas. Texas Journal of Science 46:97-

113.

Duffield, G.A., and C.M. Bull. 1998. Seasonal and ontogenetic changes in the diet of the

Australian Skink Egernia stokesii. Herpetologica 54:414-419.

Fair, W.S., and S.E. Henke. 1997. Effects of habitat manipulations on Texas Horned Lizards and

their prey. Journal of Wildlife Management 61:1366-1370.

McIntyre, N.E. 2003. Effects of conservation reserve program seeding regime on harvester ants

(Pogonomyrmex), with implications for the threatened Texas Horned Lizard

(Phrynosoma cornutum). The Southwestern Naturalist: 48:274-313.

Milne, L.J., and M.J. Milne. 1950. Notes on the behavior of horned toads. American Midland

Naturalist 44:720-741.

Montanucci, R.R. 1989. The relationship of morphology to diet in the horned lizard genus

Phrynosoma. Herpetologica 45:208-216.

Pianka, E.R., and W.S. Parker. 1975. Ecology of horned lizards: a review with special reference

to Phrynosoma platyrhinos. Copeia 1975:141-162.

Sherbrooke, W.C. 2003. Introduction to Horned Lizards of North America. California Natural

History Guides No. 64. University of California Press, Berkeley, California.

Suarez, A.V., J.Q. Richmond, and T.J. Case. 2000. Prey selection in horned lizards following the

invasion of Argentine ants in southern California. Ecological Applications 10:711-725.

Whitford, W.G., and M. Bryant. 1979. Behavior of a predator and its prey: the horned lizard

(Phrynosoma cornutum) and harvester ants (Pogonomyrmex spp.). Ecology 60:686-694.

CONCLUSIONS AND RECOMMENDATIONS FROM THE PRESENTED STUDIES OF BLAINVILLE'S

HORNED LIZARD (PHRYNOSOMA BLAINVILLII) IN THE SOUTHERN SAN JOAQUIN VALLEY,

CALIFORNIA

The lack of information on the general ecology of P. blainvillii, particularly in the San

Joaquin Valley of California, hampers the ability to make wise management decisions regarding this important and threatened species. Land conversion for agricultural and urban uses has resulted in profound habitat loss. The predicted human population growth in the San Joaquin

Valley will most likely have negative impacts on the lizard's population, particularly in terms of habitat changes. Without knowledge of general ecology and habitat needs, land managers and owners are at a disadvantage when faced with making decisions on how to best monitor, restore, or conserve suitable habitat to prevent further decline in P. blainvillii populations. Field data from the present study provided baseline information on population characteristics, habitat use and preference, activity patterns, and home range estimates that can help create local land management strategies, evaluate the impacts of continued surface disturbances, as well as contribute to the larger effort to monitor P. blainvillii population status throughout its range.

HOME RANGE

The recent advancement in telemetry technology that produced a transmitter small enough and light enough to use safely on a small animal such as the horned lizard has been vital to gathering information that previously was difficult to obtain. Using a small transmitter, I was

able to collect data from 10 lizards from two study sites (five at each site) in the southern San

Joaquin Valley. I was able to estimate a mean home range size of 5.0 ha using the Minimum

Convex Polygon (MCP) method. For comparative purposes, I also used a relatively new home

range estimator, Fixed-k LoCoH (LoCoH), that is able to eliminate areas within a home range that lizards don't use, therefore providing a more accurate estimate (Getz and Wilmers 2004;

Getz et al. 2007). In this study, LoCoH did not produce a significantly different estimate of

home range size. This is most likely due to the topography of our study sites. Areas that animals

do not use within their home range may be bodies of water, rock outcrops, or structural

buildings. Neither study site contained any of these or other obstacles, thereby eliminating the

advantage of LoCoH. The MCP method has been criticized for being sensitive to outlying points

resulting in larger range estimates that are too large; so many researchers attempt to eliminate

outliers by using a 95% estimate (Samuel and Fuller 1996). Out of the 10 lizards, I had only

three that had one point each that could be considered an outlier. I concluded that the 100%

MCP method was the most suitable for this study and I would recommend its use in future home

range studies of P. blainvillii in the southern San Joaquin Valley when there are no foreseeable

obstacles and few outliers in the data.

Small sample sizes present a problem in data analysis. Despite my attempts to attach

transmitters to more lizards, I was only able to attach transmitters to 14 lizards but get enough

data from 10 lizards. Among the 10 lizards, there was a rather broad range in home range

estimates, from 0.58 ha to 13.93 ha. I had a small sample size of observation points to use in

home range analysis, so these results should be considered a minimum home range estimate.

Phrynosoma blainvillii most likely use at least a slightly larger home range than the data show.

Clearly further studies using telemetry to estimate home ranges is needed to obtain sound data

99 that will help land managers in making decisions as to how much land is required to maintain populations of P. blainvillii in the southern San Joaquin Valley.

HABITAT USE

The use of telemetry was certainly advantageous when studying habitat use and preference of the extremely cryptic P. blainvillii, a trait that has been a hindrance in obtaining reliable life history data. I was able to remove observer bias based on sightability and find lizards whether they were above ground and active, in the cover of shrubs or other vegetation, in a rodent burrow, or buried in substrate. The results show that when above ground and active, P. blainvillii preferred microhabitat of bare ground. An affinity for bare ground microhabitat has been previously reported for P. blainvillii and other species of horned lizards as well (Whiting et al. 1993; Fair and Henke 1997; Hager and Brattstrom 1997; Montgomery and Mackessy 2003;

Gerson 2011). I saw differences in habitat use between the two study sites. At one site,

Semitropic, the lizards used bare ground most often, but used shrub cover almost equally as often. At the second site, Atwell, the lizards used bare ground most often but used shrubs much less frequently. Given that both sites had an abundance of shrubs, the difference may have arisen from how they use their habitat for thermoregulation and predator avoidance. At the Semitropic site, I found lizards using shrubs when surface temperatures were high. At the Atwell site, I found lizards using rodent burrows most often when the temperatures were high. Also at Atwell,

I noticed that when I approached the lizards close enough for them to flee; they fled to shrubs more often than they fled to rodent holes. This behavior might explain the discrepancy in microhabitat use between the two sites. Considering their dorso-ventrally flattened body shape,

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it is not surprising that P. blainvillii avoided areas of dense vegetation at both sites. The main

prey of horned lizards is native harvester ants (Pogonomyrmex spp.) and smaller native ant

species (Suarez and Case 2002; Stebbins 2003; Sherbrooke 2003). Harvester ants are granivores and they are most often in areas of bare ground with sparse vegetation (Erickson 1971; Whiting et al. 1993). Areas with bare ground, a shrub component, rodent burrows, and native ants present would be worthy of conservation consideration or land should be managed to maintain these components.

HABITAT PREFERENCE

At the Atwell site, I recorded the locations of telemetered and non-telemetered lizards and

uploaded them into ArcMap GIS, using a soil series base layer. I was able to see that 98% of the

lizard locations were in the Sandridge loamy fine sand soil series type, despite this soil type

making up approximately half of the total area. Of all the soil types at Atwell, Sandridge has the

highest permeability and drainage (Soil Survey Staff, Natural Resources Conservation Service,

United States Department of Agriculture 2010). These soil characteristics may enhance the hatching success of the eggs. Moisture content of the nest site is a critical factor in embryonic development (Muth 1980). Eggs that lose too much moisture become desiccated, which can be lethal to the embryo (Muth 1980; Sherbrooke 2003). In contrast, eggs that are hyper-hydrated

risk an increase of fungal infections and reduced gas exchange (Warner and Andrews 2002).

Soils that have a clay or silt component are less permeable and have slower drainage than sandy

soils (Soil Survey Staff, Natural Resources Conservation Service, United States Department of

Agriculture 2010). At the Atwell site, the Sandridge soil series was adjacent to Westcamp silt

101 loam, a soil that has a clay component. Despite being adjacent to the Sandridge soil and making up almost the other 50% of the soil series at Atwell, we saw only one lizard on the Westcamp soil. This suggests that lizards are avoiding Westcamp soil. Without further study, I can only infer that perhaps the sandy characteristics of Sandridge soil rather than the clay loam characteristics of the Westcamp soil are preferable to P. blainvillii. Knowledge of habitat preference can help predict presence or absence of P. blainvillii in the southern San Joaquin

Valley and aid land managers in acquiring, maintaining, or restoring critical habitat. Because this is a baseline study, I merely suggest that land consisting of soils with a higher permeability and drainage class may be considered a priority for horned lizard habitat.

ACTIVITY PATTERNS

Activity patterns are an important characteristic of horned lizard behavior and ecology that can reveal how the lizards relate to their surrounding environment. Because P. blainvillii is ectothermic and relies on outside sources to maintain body temperatures, they must thermoregulate by modifying their daily and seasonal activity patterns according to surface and ambient temperature (Smith 1946; Heath 1965; Sherbrooke 2003; Stebbins 2003). Some of the activity patterns of the lizards at the Atwell site mirrored what has been reported as typical behavior for the species. The adult horned lizards were most active in April and May while young horned lizards were most active in August and September. All age classes of P. blainvillii were most often above ground and active at surface temperatures of 28–34°C. Daily aboveground peak activity times changed with the seasons. Phrynosoma blainvillii at Atwell revealed some activity patterns that differ from what has been commonly reported as typical

102 horned lizard behavior. For example, many horned lizard species, including P. blainvillii, are reported to have a unimodal daily activity pattern in the cooler months of spring and fall; that is, they are steadily active throughout the day (Heath 1965; Pianka and Parker 1975; Hager and

Brattstrom 1997; Montgomery and Mackessy 2003). In contrast, P. blainvillii at our site did not remain steadily active throughout the morning in the spring and fall; rather, they had periods where activity noticeably peaked for a few hours then dropped off considerably midday. In the spring, the morning activity hours peaked at 0900–1100, in summer, it was 0900–1000, and in fall, it was 0900–1300. During the hottest month of summer, July, lizards were hardly active at all. This information on activity patterns can be useful in making decisions on land use and conservation practices within P. blainvillii habitat in the southern San Joaquin Valley. Land managers can use this information to conduct presence/absence surveys, schedule maintenance and other activities to minimize the impacts on P. blainvillii, and to educate recreationists such as bikers and off-road vehicle users to the times that P. blainvillii are above ground and in areas of open habitat such as roads and trails.

DEMOGRAPHICS AND MORPHOLOGY

Demographic and morphologic characteristics of horned lizards can vary intraspecifically within their range (Montgomery and Mackessy 2003; Endriss et al. 2007). I found that the P. blainvillii population at Atwell was significantly smaller in terms of average snout-vent length

(SVL) than a population in southern California (Hager 1992). The maximum female SVL at

Atwell was 85 mm while the southern California population reported a maximum female SVL of

103.0 mm (Hager 1992). Adult female horned lizards are atypical among vertebrates in that they

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are larger than the males, and this was certainly true at the Atwell site. The average adult female

SVL was 72.3 mm and average male SVL was 68.8 mm. Whereas adult SVL sizes at the Atwell

site differed from other populations of P. blainvillii on a spatial scale, the average hatchling size

of 25–31 mm SVL (Howard 1974; Hager 1992; Gerson 2011) is relatively consistent across

latitudes and the smallest lizards I found were accordant with that range. The range of P.

blainvillii extends across a long portion of west and central California and the northwest tip of

Baja California and includes a wide variety of habitats and climatic conditions. Because P. blainvillii occurs in a variety of habitat types, being knowledgeable of these life-history traits as they pertain to a particular locale of the population of concern is critical. For P. blainvillii, a one-size fits all approach to management and conservation is not appropriate. Only localized

demographic and ecological data for P. blainvillii from the San Joaquin Valley likely will help

clarify conservation needs for this species.

In the past 100 to 150 years, the San Joaquin Valley has experienced an astounding loss

of natural communities. Human population growth in the Central Valley is predicted to occur at

one of the fastest rates of any region in California (California Department of Finance 2012).

Scientists and land managers are obligated to present their professional opinion on the impact

these increasing pressures place on sensitive species such as the P. blainvillii. However, the lack

of comprehensive data on the basic needs of P. blainvillii in the San Joaquin Valley results in an

uncertain future for a species already experiencing dramatic population declines throughout its

range. It is hoped that the baseline information provided from my research will contribute

valuable and useful knowledge of the general ecology that will assist in conservation efforts of P.

blainvillii in the southern San Joaquin Valley.

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