Society for the Study of Amphibians and Reptiles

Society for the Study of Amphibians and Reptiles Male Texas Horned Lizards Increase Daily Movements and Area Covered in Spring: A Mate Searching Strategy? Author(s): Richard C. Stark, Stanley F. Fox, David M. Leslie Jr. Source: Journal of Herpetology, Vol. 39, No. 1 (Mar., 2005), pp. 169-173 Published by: Society for the Study of Amphibians and Reptiles Stable URL: http://www.jstor.org/stable/4092970. Accessed: 18/01/2011 16:05 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at. http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at. http://www.jstor.org/action/showpublisher?publishercode=ssar.. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Society for the Study of Amphibians and Reptiles is collaborating with JSTOR to digitize, preserve and extend access to Journal of Herpetology. http://www.jstor.org

SHORTER COMMUNICATIONS 169 and Girard, in north-central Oregon. Northwest Science 50:243-260. PORTER, W. P., AND C. R. TRACY. 1983. Biophysical analyses of energetics, time-space utilization, and distributional limits. In: R. B. Huey, E. R. Pianka, and T. W. Schoener (eds.), Lizard Ecology: Studies of a Model Organism, pp. 55-82. Harvard Univ. Press, Cambridge, MA. ROFF, D. A. 2002. Life History Evolution. Sinauer Assoc., Sunderland, MA. SINERVO, B., AND D. F. DENARDO. 1996. Costs of reproduction in the wild: path analysis of natural selection and experimental tests of causation. Evolution 50:1299-1313. SINERVO, B., AND P. DOUGHTY. 1996. Interactive effects of offspring size and timing of reproduction on offspring reproduction: experimental maternal, and quantitative genetic aspects. Evolution 50: 1314-1327. TINKLE, D. W. 1967. The life and demography of the Side-Blotched Lizard, Uta stansburiana. Miscellaneous Publications of the Museum of Zoology, Univ. of Michigan. 132:1-182. TURNER, F. B., G. A. HODDENBACH, P. A. MEDICA, AND J. R. LANNOM. 1970. The demography of the lizard, Uta stansburiana Baird and Girard, in southern Nevada. Journal of Animal Ecology 39:505-519. WILSON, B. S. 1991. Latitudinal variation in activity season mortality rates of the lizard Uta stansburiana. Ecological Monographs 61:393-414. Accepted: 5 November 2004. Journal of Herpetology, Vol. 39, No. 1, pp. 169-173, 2005 Copyright 2005 Society for the Study of Amphibians and Reptiles Male Texas Horned Lizards Increase Daily Movements and Area Covered in Spring: A Mate Searching Strategy? RICHARD C. STARK,1'2 STANLEY F. Fox,3 AND DAVID M. LESLIE JR.4 1Department of Zoology and Oklahoma Cooperative Fish and Wildlife Research Unit, Oklahoma State University, Stillwater, Oklahoma 74078, USA 3Department of Zoology, Oklahoma State University, Stillwater, Oklahoma 74078, USA; E-mail: foxstan@okstate.edu 4United States Geological Survey, Biological Resources Division, Oklahoma Cooperative Fish and Wildlife Research Unit, Stillwater, Oklahoma 74078, USA; E-mail: cleslie@usgs.gov ABSTRACT.-Texas Horned Lizards, Phrynosoma cornutum, were tracked using fluorescent powder to determine exact daily movements. Daily linear movements and daily space use were compared between adult males and females. Lizards that traveled the greatest linear distances also covered the largest areas. In Oklahoma, adults emerge from hibernation in late April and early May and mate soon afterward. Males traveled significantly greater distances (and covered significantly larger areas in a day) than females in May but not after May. We propose that males move more and cover more area than females early in the mating season to intercept receptive females. Cryptic characteristics and small size of many amphibians and reptiles make them difficult to track (Zug, 1993). Recently, techniques such as radiotelemetry (Fisher and Muth, 1995; Fair and Henke, 1999) and fluorescent powder (Lemen and Freeman, 1985; Blankenship et al., 1990; Dodd, 1992; Butler and Graham, 1993; Keller, 1993; Stark and Fox, 2000) have allowed researchers to track small and cryptic species. Previously, researchers have gained information on daily movements of Texas Horned Lizards, Phrynosoma cornutum, by adding linear distances between radio- 2 Present address: United States Fish and Wildlife Service, Oklahoma Ecological Services, 222 South Houston Avenue, Suite A, Tulsa, Oklahoma 74127, USA; E-mail: richard_stark@fws.gov locations for each day of radiotelemetry (Fair and Henke, 1999) and through observations (Whitford and Bryant, 1979), but those methods have disadvantages. It is likely that the distance covered by a lizard between two points is greater than a straight line between them, and presence of an observer may affect behavior of an animal. A lizard's daily movements are generally for predator avoidance, feeding, thermoregulation, and mating. Knowledge of daily space use is important because it gives insight into a species' life history and selective pressures. For example, space use might reflect differences in reproductive strategies between the sexes. The activity area, defined as the area in which a lizard occurs during a specific time period (e.g., a day, a week, etc.), is often larger in male lizards (Rose, 1982). The difference may increase during the breeding season

170 SHORTER COMMUNICATIONS if males expand their territories to overlap more females, or if males traverse larger areas than females to search for receptive females. We examined space and habitat use of Texas Horned Lizards in north-central Oklahoma. This species was once abundant in Oklahoma (Price, 1990) but has declined in abundance and distribution in the state over the past several decades; similar trends have occurred in Texas (Donaldson et al., 1994). Currently, the Texas Horned Lizard is a species of special concern in Oklahoma and threatened in Texas. MATERIALS AND METHODS Statistical Analyses.-Linear regression analyses were used to test for inconsistencies between daily linear distances traveled and daily activity areas, and for a relationship between distances traveled by adult lizards (standardized as [(Xi- mean)]/sd, where Xi is distance traveled by an individual and SD is standard deviation of the sex/site class to which that individual belongs) and time of day when the lizards were dipped and released. Mann-Whitney U-tests were used to investigate whether time of day dipped differed between sexes. We pooled data by site and year for each sex to compare daily linear distances traveled and daily areas covered between sexes. Analysis of variance (ANOVA) was used to test the appropriateness of pooling data. This analysis used only post-may data because data from SF were entirely post-may. Mann-Whitney U-tests were used to compare daily linear distances traveled and daily activity areas between males and females. Significance (at the 0.05 overall level) was determined using the sequential Bonferroni procedure for two related tests (Rice, 1989): daily linear distances traveled and daily activity areas. Study Areas.-We conducted the study in Payne County, Oklahoma, on two study sites (36006'30"N and 97'01'30"W) that we named Antique Field (AF) and South Field (SF). Both sites had flat terrain and areas of dense grass and herbaceous vegetation and open areas of bare ground and sparse vegetation. AF was a 2-ha site dominated by little bluestem (Schizachyrium scoparium), silver bluestem (Bothriochloa saccharoides), and switchgrass (Panicum virgatum). Dominant forbs were Himalayan bush clover (Lespedeza cuneata), Illinois Daily linear movements and daily activity areas were both assessed because it is bundleflower (Desmanthus illinoensis), and western theoretically possible for a lizard to travel a ragweed (Ambrosia psilostachya). Lizards were tracked greater linear distance than another during two field seasons: 2 May through 6 August 1998 lizard but to cover a smaller area if that individual remained in a small area and often crossed its own trail, and 8 May through 25 July 1999. SF was a 4.4-ha site whereas the other individual tended to travel to new about 0.40 km southwest of AF. Dominant grasses at SF areas. were little bluestem, Japanese brome Only (Bromus japonicus), lizards that were tracked to their sleeping and tall dropseed (Sporobolus asper). Dominant forbs spots (i.e., end of the day's trail where the lizard had taken cover for the were annual broomweed night), or lizards not tracked to their (Gutierrezia dracunculoides), Himalayan bush clover, and western ragweed. Lizards sleeping spots but that moved > 50 m were used in were tracked at SF only during the second field season: analyses (91.2% of tracking instances used in the 28 May through 25 July 1999. analyses were to sleeping spots). Averages were used for lizards tracked on more than one occasion. For one Tracking.-To locate lizards, we used visual searches female, we could not include data for a that consisted of 1-3 researchers walking parallel lines daily activity area because she was tracked until the entire study area was searched. We located 16 only once and the short linear distance traveled did not allow for the deadult horned lizards at AF in 1998 (four females and 12 lineation of an area males) and 16 in 1999 (10 females and six males). At polygon. SF, we located 13 adult horned lizards (six females and Mann-Whitney U-tests also were used to compare the use of seven males) in 1999. Toe clips were used for individual open, sparsely vegetated areas and densely identification. During daylight hours, we vegetated dipped areas early in the mating season (i.e., May) and well into the active season (i.e., after lizards in flourescent powder and released them at May) by males and between sexes. The data used for the the place of capture (Stark and Fox, 2000). The lizards analyses consisted of the were held by the head while dipping them to percentage of the flags from a lizard's prevent trail that occurred in powder from entering their eyes, nares, and ear just one macrohabitat, the open openings. The trail of powder was tracked that category (since the percentage in the densely vegetated night with the aid of a portable ultraviolet lamp, and a marker category would be the exact complement). These data flag was placed in the were examined to look for evidence that (1) males ground every 5 m along the trail selected habitat that enhanced visual detection and, of powder to determine daily linear movements of the hence, encounters with lizards (Fig. 1). We also recorded the macrohabitat in receptive females more so early in the which each marker flag occurred. Macrohabitat was breeding season when more females would be either scored as receptive, and (2) males selected habitat that enhanced open (sparsely vegetated, open areas/ visual detection more than females because males, and bare ground) or densely vegetated (grassy and herba- not females, were ceous vegetation), depending on the actively searching for mates. SYSTAT predominant (L. Wilkinson, SYSTAT: The characteristics of the site. System for Statistics. We set up a grid system on each SYSTAT, Inc., Evanston, IL, 1990) was used for study site using statistical analyses. survey equipment so that the X-Y coordinates of all lizard locations could be determined. The ArcView RESULTS animal movements extension (P. N. Hooge and B. Eichenlaub, Animal movement extension to ArcView, Inconsistencies between daily linear distance traveled vers. 1.1. Alaska Biological Science Center, U.S. Geo- and size of the daily activity area were not observed. logical Survey, Anchorage, 1997) was used to delineate Lizards that traveled the greatest linear distances also daily activity areas used by lizards using 100% covered the largest areas (r = 0.75, df = 45, P < 0.001). minimum convex polygons. Contrary to our expectations, distances traveled by

SHORTER COMMUNICATIONS 171 10 0 10 20 Meters FIG. 1. Path of an adult female Texas Horned Lizard at AF on 22 July 1999. White represents sparsely vegetated/open areas; pattern indicates areas of relatively dense vegetation; star shows where the lizard stopped to take cover for the night. adult lizards were not related to time of day when the lizard was dipped and released (r = 0.002, df = 95, P = 0.99). Time of day that an individual was dipped did not differ between sexes (U = 1069.0, c2 = 0.60, df = 1, P = 0.44). The daily linear distances traveled did not differ between years for males (N = 25, F = 2.92, P = 0.10) or females (N = 21, F = 0.02, P = 0.87). Daily linear distances traveled also did not differ between sites for males (N = 15, F = 1.65, P = 0.22) or females (N = 15, F = 0.26, P = 0.58). Size of daily activity areas did not differ between years for males (N = 25, F = 2.44, P = 0.13) or females (N = 20, F = 0.215, P = 0.65) or between sites for males (N = 15, F = 1.77, P = 0.21) or females (N = 15, F = 0.36, P = 0.56). Thus, we pooled data from the two years and two sites, for each sex, for statistical comparison of movements and space use by each sex. Average individual daily linear movements for all lizards was 45.0 m (range = 10-220 m). Males moved significantly further than females in May (U = 1.5, c2 = 9.70, df = 1, Bonferroni-corrected P < 0.05) but not after May (U = 124.0, c2 = 0.23, df = 1, Bonferroni-corrected P > 0.05) when their average daily movements were very similar (Fig. 2). The average individual daily activity area for all lizards was 232.8 m2 (range = 1.7-3011.4 m2). Males covered drastically larger areas in a day during May than females (U = 3.0, c2 = 8.58, df = 1, Bonferronicorrected P < 0.05) but not after May (U = 105.5, c2 = 0.0, df = 1, Bonferroni-corrected P > 0.05; Fig. 3). The trail of male lizards in the early mating season (i.e., May) did not occur in open, sparsely vegetated areas and densely vegetated areas differently than they did well into the active season (i.e., after May; U = 23.5, c2 = 0.02, df = 1, P = 0.89). Trails of males and females also did not differ in this regard in May (U = 12.0, c2 = 1.8, df = 1, P = 0.18) or after-may (U = 80.0, c2 = 2.1, df = 1, P = 0.14). DIscussIoN Our results for the overall average daily movements of Texas Horned Lizards (mean = 45.0; range = 10-220 m) are similar to previous studies. Fair and Henke (1999) reported an average movement of 36.5 m/day (range = 0.0-246.7 m), and Whitford and Bryant (1979) reported an average of 46.8 m/day (range = 9-91 m). Distances traveled by adult lizards were not related to time of day when the lizard was dipped in fluorescent powder and released (i.e., those dipped and released later in the day did not travel less than those dipped and released earlier in the day). Lizards that were captured, dipped, and later tracked were those active during our visual searches (except for lizards dipped at the place they took cover the previous evening). It is likely that activity of adult lizards is influenced by multiple factors, such as the thermal

172 SHORTER COMMUNICATIONS 120 Males? 100 E] Females S40 so80 60 20 0 May Post-May FIG. 2. Mean daily linear distances traveled by males and females during May (10 males and six females) and after May (15 males and 15 females). Vertical lines are 1 SE. environment, need for food, and mating condition, such that adult lizards are not always active throughout an entire day. Texas Horned Lizards mate soon after they emerge from hibernation in late April and May (Ballinger, 1974), and, in this study, male lizards moved greater distances and covered larger areas than females during this time but not later. Although the mating system of Texas Horned Lizards is unknown, we propose that male lizards travel considerable distances early in the season to locate females to increase chances of copulating with multiple females or at least encountering a receptive, nongravid female, for which the duration of receptivity may be brief (Montanucci and Baur, 1982). This hypothesis seems to conform to other aspects of their natural history. Texas Horned Lizards occur in grassland and desert-shrub communities where typical habitat is a patchwork of bare ground and vegetation. Because ground-level vegetation limits visibility for horned lizards (which do not survey from elevated perches), it is reasonable that males must move around more in the breeding season to find females. Texas Horned Lizards are reported to reduce overlap of home ranges with conspecifics, either through voluntary mutual avoidance or a low level of territoriality (Munger, 1984). Although the space use of P. cornutum is not well known, males certainly do not exhibit the same strong territoriality as seen in other phrynosomatid lizards (Stamps, 1977). Phrynosoma cornutum does, however, appear to occupy exclusive weekly transitory home ranges where individual lizards occupy only a part of their complete home range for several days and then move to a new section for several days, possibly to locate areas with un- harvested and/or replenished prey items (Fair and Henke, 1999). Thus, individuals are dispersed across suitable habitat, and because males do not defend territories that hold or attract females, males must search for receptive females in the early part of the breeding season to successfully reproduce. Sherbrooke (2002b) found a seasonally skewed malebiased sex ratio of road-collected Texas Horned Lizards in the peak of the mating season but not immediately before or after this time. He hypothesized that the skewed sex ratio may be a result of (1) males increasing movements in the mating season to locate more females, and, consequently, encountering roads more frequently than females, and/or (2) males spending relatively longer periods of time on roads that provide 1000 900 " 800 S400 700 600 500 300 c 200 S 100. o May 00Males ] Females Post -May FIG. 3. Mean daily area covered by males and females during May (10 males and six females) and after May (15 males and 14 females). Vertical lines are 1 SE. open areas where it would be easier to visually locate females. We found no difference in the use of open versus closed areas between males (or between the sexes) early in the mating season compared to well into the active season. The proportion of total daily movements by a lizard that occurs in open areas does not appear to be related to sex or season. Although our data provide valuable information on exact daily move- ments and the type of habitat through which lizards moved, we do not know the duration of time spent in a particular habitat. We believe that males increase movements in the mating season to locate more females (as per hypothesis 1 of Sherbrooke, 2002b). Whether they spend more time in open areas to increase odds of visually locating mates (as per hypothesis 2 of Sherbrooke, 2002b) remains to be tested. Males do not, however, appear to travel in the open more than females during the breeding season. Although it has been predicted that the shape of a Texas Homed Lizard's body would make travel through dense vegetation difficult (Whiting et al., 1993; Fair and Henke, 1997), we found that Texas Horned Lizards often traveled through areas of dense vegetation for extended distances rather than just entering vegetation to take refuge near an open area (Stark, 2000). Such behavior may be adaptive because vegetation provides cover from stressful environmental conditions (e.g., hot and/or dry periods of the day). Also, traveling through dense vegetation for at least a portion of their route rather than entirely in the open may, at times, be advantageous for this highly cryptic and relatively slow lizard because extended movement in the open is more likely to attract the attention of a predator. Dense vegetation provides cover to horned lizards. Also, the white middorsal stripe of the Texas Horned Lizard may mimic old grass-stems (Sherbrooke, 2002a) and, therefore, enhance their crypsis when they occur in grassy areas. In almost every species of Phrynosoma, including P. cornutum, the female is the larger sex (Pianka and Parker, 1975; Zamudio, 1996). Female-biased sexual size dimorphism (SSD) is usually explained by either the "fecundity advantage hypothesis," in which selective pressures favor large females and therefore, higher fecundity, or the "small male advantage hypothesis," in which selective pressures favor small male body size because (1) males that mature early and at a smaller size may have increased lifetime reproductive success -

SHORTER COMMUNICATIONS 173 and/or (2) the increased mobility and endurance likely to occur in small males over large males would benefit males searching for dispersed females (Zamudio, 1998). Zamudio (1998) concludes that the "small male advantage hypothesis" better explains female-biased SSD in Phrynosoma. In other words, although larger females benefit from higher reproductive output, changes in female body size likely do not account for the observed female-biased SSD. There seems to be more selective pressure for small males. Our study supports the small, mobile-male advantage hypothesis by documenting that males travel considerable distances early in the mating season. Acknowledgments.-Financial support was provided by the Wildlife Diversity Program of the Oklahoma Department of Wildlife Conservation, the Department of Zoology at Oklahoma State University, and the Oklahoma Cooperative Fish and Wildlife Research Unit (Oklahoma State University, Oklahoma Department of Wildlife Conservation, U.S.G.S. Biological Resources Division, and Wildllife Management Institute, cooperating). State of Oklahoma Scientific Collector's Permits were required and obtained for this study. All applicable institutional Animal Care guidelines were followed. We thank ARC Communities and Lambert Construction for allowing us to conduct the study on their properties. We also thank J. Dyer, M. Sivils, and J. Hackler for their valuable help in the field. LITERATURE CITED BALLINGER, R. E. 1974. Reproduction of the Texas Horned Lizard, Phrynosoma cornutum. Herpetologica 30:321-327. BLANKENSHIP, E. L., T. W. BRYAN, AND S. P. JACOBSEN. 1990. A method for tracking tortoises using fluorescent powder. Herpetological Review 21:88-89. BUTLER, B. O., AND T. E. GRAHAM. 1993. Tracking hatchling Blanding's Turtles with fluorescent pigments. Herpetological Review 24:21-22. DODD JR., C. K. 1992. Fluorescent powder is only partially successful in tracking movements of the Six-Lined Racerunner (Cnemidophorus sexlineatus). Florida Field Naturalist 20:8-14. 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 46:96-113. FAIR, W. S., AND S. E. HENKE. 1997. Efficacy of capture methods for a low density population of Phrynosoma cornutum. Herpetological Review 28:135-137.. 1999. Movements, home ranges, and survival of Texas Horned Lizards (Phrynosoma cornutum). Journal of Herpetology 33:517-525. FISHER, M., AND A. MUTH. 1995. A backpack method for mounting radio transmitters to small lizards. Herpetological Review 26:139-140. KELLER, C. 1993. Use of fluorescent pigment for tortoise nest location. Herpetological Review 24:140-141. LEMEN, C. A., AND P. W. FREEMAN. 1985. Tracking mammals with fluorescent pigments: a new technique. Journal of Mammalogy 66:134-136. MONTANUCCI, R. R., AND B. E. BAUR. 1982. Mating and courtship-related behaviors of the Short Horned Lizard, Phrynosoma douglassi. Copeia 1982:971-974. MUNGER, J. C. 1984. Home ranges of horned lizards (Phrynosoma): circumscribed and exclusive? Oecologia 62:351-360. PIANKA, E. R., AND W. S. PARKER. 1975. Ecology of horned lizards: a review with special reference to Phrynosoma platyrhinos. Copeia 1975:141-162. PRICE, A. H. 1990. Phrynosoma cornutum (Harlan) Texas Horned Lizard. Catalogue of American Amphibians and Reptiles 469.1-469.7. RICE, W. R. 1989. Analyzing tables of statistical tests. Evolution 43:223-225. ROSE, B. 1982. Lizard home ranges: methodology and functions. Journal of Herpetology 16:253-269. SHERBROOKE, W. C. 2002a. Do vertebral-line patterns in two horned lizards (Phrynosoma spp.) mimic plantstem shadows and stem litter? Journal of Arid Environments 50:109-120.. 2002b. Seasonally skewed sex-ratios of roadcollected Texas Horned Lizards (Phrynosoma cornutum). Herpetological Review 33:21-24. STAMPS, J. A. 1977. Social behavior and spacing patterns in lizards. In C. Gans and D. W. Tinkle (eds.), Biology of the Reptilia. Vol. 7, pp. 265-334. Academic Press, London. STARK, R. C. 2000. Habitat Use, Daily Movements, and Body Size of the Texas Horned Lizard in North- Central Oklahoma. Unpubl. master's thesis, Oklahoma State Univ., Stillwater. STARK, R. C., AND S. F. Fox. 2000. Use of flourescent powder to track horned lizards. Herpetological Review 31:230-231. 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. WHITING, M. J., J. R. DIXON, AND R. C. MURRAY. 1993. Spatial distribution of a population of Texas Horned Lizards (Phrynosoma cornutum: Phrynosomatidae) relative to habitat and prey. Southwestern Naturalist 38:150-154. ZAMUDIO, K. R. 1996. Ecological, Evolutionary, and Applied Aspects of Lizard Life Histories. Unpubl. Ph.D. diss., Univ. of Washington, Seattle.. 1998. The evolution of female-biased sexual size dimorphism: a population-level comparative study in horned lizards (Phrynosoma). Evolution 52:1821-1833. ZUG, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press, San Diego, CA. Accepted: 18 November 2004.