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Feb 28, 2011 - Habitat Use and Activity Budgets of Emerald Basilisks. (Basiliscus plumifrons) in Northeast Costa Rica. Matthew S. Lattanzio1,2 and Thomas C.
Copeia 2012, No. 3, 465–471

Habitat Use and Activity Budgets of Emerald Basilisks (Basiliscus plumifrons) in Northeast Costa Rica Matthew S. Lattanzio1,2 and Thomas C. LaDuke1 Variation in individual activity budgets may have important impacts for the long-term fitness of a population, yet our understanding of the factors shaping activity remains limited. Here, we report on intraspecific activity budget variation and the factors influencing it within a population of emerald basilisk (Basiliscus plumifrons) lizards in Costa Rica. Because behavioral variation may have a seasonal component, we monitor activity across both a wet and dry season. All basilisks exhibited similar frequencies of behavior throughout the day, with the exception of foraging rate. Adult females foraged more often than adult males or juveniles, possibly to satisfy higher expected energetic demands during the reproductive season. Juvenile and adult lizards occupied separate habitats characterized by significant differences in vegetation structure. In particular, juvenile lizards were more frequently observed in open, grassier habitats that were closer to water than adults. Juveniles may reduce their chances of predation by or competition with larger individuals in these areas, or may simply frequent those areas to take advantage of the size-dependent water-running ability characteristic of this species. As the area shifted from a wet to a dry period, juvenile activity significantly declined and by the end of the study very few juveniles were encountered. Adult lizards did not exhibit reduced activity per se, but instead shifted the timing of peak activity into early-morning and late-afternoon periods. Although activity budgets were largely similar among juveniles and adults, our findings highlight both ontogenetic variation in habitat use and the influence of seasonal variation on basilisk activity.

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ARIATION in individual activity budgets can have important fitness implications depending on how organisms balance their time spent acquiring energy with alternative needs, such as antipredation behavior or territorial defense (McNamara and Houston, 1986). Historically, studies of activity in ectotherms based research on the assumption that opportunistic behavior is adaptive (Huey, 1982), and thus animals should be active whenever possible. Over the past 30 years research has demonstrated that the relationship between activity and inactivity is much more behaviorally complex (Rose, 1981; Bachman, 1993; Watters, 2009). Most of our knowledge of activity budget variation draws from studies focused on either the influence of multiple factors on one or two behavioral components of a species’ entire activity budget (Skelly and Werner, 1990; Bachman, 1993), or the influence of only a few factors on multiple behavioral components (Owen-Smith, 1998; Sperry et al., 2010). A combination approach is critical toward our understanding of mechanisms generating observed activity variation. The use of any one behavior forces trade-off decisions against other behaviors (e.g., vigilance and foraging behavior: Bachman, 1993), and thus all behaviors exhibited need to be monitored. Furthermore, there are usually multiple factors associated with the current situation or context that can influence those tradeoffs (Sperry et al., 2010). Influential factors generally fall within one of two categories: intrinsic and extrinsic. Intrinsic factors include ontogenetic parameters such as age and reproductive status (see Watters, 2009), and sex (Eifler et al., 2007). Extrinsic factors may include the presence of competitors (Bohlin, 1977), risk of predation (Bachman, 1993; Whittingham and Evans, 2004), habitat structure (Pringle et al., 2003), prey availability (Diehl, 1993), and climate (Adolph and Porter, 1993). Furthermore, both categories of factors likely interact to generate the observed diversity in activity budgets within a species (Watters, 2009). 1

Here we focused on quantifying activity budget variation and the intrinsic and extrinsic factors associated with that variation in a sit-and-wait foraging lizard, the emerald basilisk (Basiliscus plumifrons) in northeastern Costa Rica. Sit-and-wait foragers like B. plumifrons must balance their time between movement (necessary to patrol a territory or thermoregulate), foraging effort, and vigilance behavior (scanning for predators or competitors). Because adults reproduce year-round (Savage, 2002), and juveniles may avoid areas occupied by adult lizards (Hirth, 1963; Greene et al., 1978), we divided lizards into juvenile and adult (male or female) classes and included habitat (micro-, macro-, and regional scale) as factors. We monitor activity relative to prevailing climate and season (wet and dry) because lizard activity is likely dependent on ambient conditions (Adolph and Porter, 1993), and variation thereof (Fleming and Hooker, 1975). MATERIALS AND METHODS Study site.—We collected data on a population of B. plumifrons (n 5 84) at El Zota Biological Field Station in northeastern Costa Rica (10u57.69N, 83u75.99W), from 8 May–23 August 2005 and from 19 December 2005–21 January 2006. El Zota encompasses approximately 1,000 ha of lowland tropical wet forest, and is one of the largest privately owned biological field stations in Costa Rica (Pruetz and LaDuke, 2001). At least 700 ha of the station property are dominated by mature and secondary forest, and the remaining 300 ha are a patchwork of lagoons, pastures, swamp forest, and reforested cropland. Approximately 8.5 km of trails that traverse these different habitats have been cut to facilitate ecological research (Lindshield and Rodrigues, 2009). The weather is warm and humid, ranging 20–33.8uC daily. Seasonality in this region is limited, marked by rainy periods in early summer (April–June) and late fall (November–December), which are interrupted by

Department of Biological Sciences, East Stroudsburg University of Pennsylvania, East Stroudsburg, Pennsylvania 18360; E-mail: [email protected]. 2 Present address: Department of Biological Sciences, Ohio University, Athens, Ohio 45701; E-mail: [email protected]. Send reprint requests to this address. Submitted: 28 February 2011. Accepted: 4 April 2012. Associate Editor: K. Martin. DOI: 10.1643/CP-11-025 F 2012 by the American Society of Ichthyologists and Herpetologists

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dry periods. During this study, July–August were unusually dry. Study species.—Emerald basilisks (Basiliscus plumifrons) are abundant and widely distributed throughout the lowland tropical forests of Costa Rica (Savage, 2002), yet we know very little about their general ecology. Although basilisks are primarily insectivorous, adults may also opportunistically consume vertebrate prey, including juvenile basilisks (Hirth, 1963; Greene et al., 1978). In addition, spatial overlap in habitat use between adults and juveniles is common (Goldfarb, 2004). Behavioral data are extremely lacking, aside from a few scattered reports on their movement and habitat use (home range: Vaughan et al., 2007), and the kinematics of their water-running ability (Hsieh and Lauder, 2004). With all of this in mind, B. plumifrons is an ideal lizard species for investigating intraspecific diversity in activity budgets. Focal lizard surveys.—We conducted nightly surveys to collect B. plumifrons lizards for morphological measurements throughout El Zota on all non-stormy nights between 1800 and 2300 h. Most nights were clear, but some steady light rain fell on a few occasions (n 5 5). Surveys were terminated in the event that rains picked up and affected visibility or became potentially dangerous (i.e., presence of lightning). During each survey, we walked slowly along trails, roadways, and waterways, and located sleeping lizards with the aid of a flashlight. We randomized search locations each night using a map of the station gridded into search areas. No site was explored more than once a week, and each lizard was captured and marked only once. We recorded the snout–vent length (SVL), head length (HL, measured from tip of snout to base of jaws), jaw width (JW, measured distance between jaws at the back of head), and body mass of each lizard we encountered. Lengths were recorded to the nearest millimeter, and mass to the nearest 0.1 gram. Adult lizards are readily distinguished from juveniles based on body size, and adult males from females based on the presence of head, dorsal, and caudal crests (males only, see Savage, 2002). As a result, juvenile lizards were not sexed. All lizards were marked with a unique black ink spot on their back or crest (both sides) to aid in individual identification. Habitat use.—Habitat data were recorded at three scales: microhabitat, macrohabitat, and region. After observation periods ceased, we recorded microhabitat-level data within a 1 m2 plot around the initial observed location of each lizard. We estimated maximum vegetation height within each plot to the nearest 0.1 m using measuring tape for grasses and low vegetation or estimated with an altimeter for understory and canopy trees over 2 m high. We categorized each plot by maximum vegetation height as grass (0–1 m), understory (1–3 m), or overstory (.3 m). We recorded the initial perch height of each focal lizard at mid-body to the nearest 0.1 m with measuring tape. We estimated percent sunlight availability (PSUN) by averaging readings from a spherical crown densiometer taken above the initial perch of the lizard and the four cardinal directions along the perimeter of the 1 m2 frame (thus, an average of five total readings). We estimated percent grass cover (PGRAS, dead or alive) within each frame by dividing it into quadrats and averaging cover variables over all four quadrats. We also recorded the number of perches present

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within the plot (PERCH) as the number of branches at least 0.5 cm in diameter. Macrohabitat level data were quantified following a protocol modified from Reinert (1984). Briefly, we recorded distance to the nearest standing water source (DWS), human disturbance (DHD), overstory tree (DNO), understory tree (DNU), and fallen tree (DFT), in meters. Human disturbances included any cleared or modified (developed or paved) areas such as the trails, road, cabins, and lagoon docks. All trees greater than 7.5 cm diameter at breast height were considered part of the overstory. For DFT, only distances to those trees with greater than 7.5 cm diameter at breast height were measured. All distances were straight-line measured from the center of the microhabitat frame (i.e., location of the lizard) to the nearest edge of the appropriate area or structure. Regional habitat categories were generated by dividing our study site at El Zota into separate survey areas based on the prevailing vegetation structure characterizing each area. These categories included Forest Edge (behind cabin area and along trails), Forest Interior (i.e., .3 m from the road, open areas, and trails), Station Road, Field (grassy vegetation .0.5 meter in height, sparse tree cover), and Lagoon (edge and central island interior with vegetation ,0.5 meter in height). Finally, we categorized environmental conditions as one of the following: sunny (no clouds), partly cloudy (clouds present at ,50% cover), mostly cloudy (between 50 and 100% cloud cover), or overcast (100% cloud cover without rain). Activity budgets.—We surveyed the road, all trails (including station boundary trails), waterways (rivers, lagoons), and fields within our designated regions at El Zota daily for B. plumifrons lizards. To minimize pseudoreplication, we randomized which region to survey each day and which time of day to begin surveys in each area. Previous work documenting movements of B. plumifrons (Goldfarb, 2004) indicated that lizards were inactive (based on radio-telemetry) at El Zota during mid-day (ca. 1130–1330 h). To investigate this claim, we conducted preliminary surveys throughout El Zota from 8–18 May from 1100–1300 h. Because we also encountered no visibly active lizards during this period, we split daytime surveys into morning (0800– 1200 h) and afternoon (1300–1700 h) survey periods, beginning on 19 May, for the remainder of the study. Thus, we searched two regions per day for basilisks (one in the morning, another in the afternoon). When we encountered an individual basilisk, we recorded its age (juvenile or adult) and sex (male or female, adults only) and commenced behavioral observations. All observations were conducted from a minimum distance of 3 m away in an attempt to avoid observer–encounter effects. We each wore similar colored and patterned clothing during all surveys. All known repeated observations of the same individual lizard were noted but not included in any statistical analyses. We recorded both frequency (number of times occurred) and duration (measured to the nearest second using a stopwatch) of each behavior we observed. We terminated observations of each focal lizard after a 40-minute period, after which we began to search for a new focal lizard. We terminated all lizard surveys at the end of its respective period (1200 h for morning and 1700 h for afternoon), unless behavioral observations on a focal lizard were in progress. In these cases we terminated surveys when the 40minute observation time was up. We recorded time spent when the lizard moved from view as a separate category

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Table 1. Morphometric Data for Those Emerald Basilisk (Basiliscus plumifrons) Lizards Collected during Nightly Surveys at El Zota Station in Northeast Costa Rica. Means are ±1.0 standard error; range in parentheses. Variable coding is as follows: snout–vent length (SVL), mass (MA), head width (HW), and jaw length (JL). Classes (juvenile and adult female or male) are in agreement with both the results of a Discriminant Function Analysis on all morphological variables collected during this project (.90% support), and with those reported in the literature (Savage, 2002).

Class designation

n

SVL (mm)

Juvenile

15

69.2 6 5.4 (47–78)

Adult Female Male Total

5 7 27

111.6 6 11 (86–141) 141 6 9.6 (104–168)

MA (g)

HW (mm)

JL (mm)

13.2 6 3.2 (2.5–40)

12.2 6 1.2 (7–14)

10.5 6 0.9 (8–13)

52 6 14.9 (19.5–91.5) 84.5 6 15.2 (27.6–127)

18 6 1.7 (14–23) 20.2 6 2.4 (13–29)

19 6 1.9 (15–24) 21.2 6 2.4 (14–32)

from other behaviors (i.e., out-of-view). If a basilisk remained out-of-view for more than ten minutes, we ceased observations on that individual and located another lizard. Statistical analyses.—We deleted the first five minutes of each observation period to avoid observer–encounter effects prior to habituation (see Hawlena and Perez-Mellado, 2009). We further discarded the last five minutes of each observation, and thus retained the central 30 minutes for statistical analysis. Of 104 total observations, 62 lizards were individually recognizable, and we focused analyses on first encounters with these individuals only. A Discriminant Function Analysis categorized this sampled population of B. plumifrons initially into two classes, based on SVL: juvenile (47–76 mm) and adult (83–168 mm). Adults were further split into male and female classes to account for potential sex-specific variation in activity. Thus, three class designations were assigned (juvenile, adult male or female), and maintained as factors in all analyses. Morphological variables are described parametrically as Mean Value 6 1.0 Standard Error (S.E.). Separate regressions were applied to assess relationships of log-transformed body mass, head width, and jaw length (dependent variables) to log-transformed snout-vent length (independent variable). Residuals from those regressions were analyzed with separate Analyses of Variance (ANOVAs) to compare sizeindependent variation in morphology among the three classes. Behavioral data did not meet assumptions of normality initially, and thus we rank-transformed each variable. We applied a General Linear Model procedure with transformed behavioral data as dependent variables and time of day (morning or afternoon) and class (juvenile, adult female or male) as fixed factors. We applied Tukey’s HSD multiple comparison tests as necessary. Relationships between activity and environmental factors were assessed with Spearman’s rho correlation coefficients. Seasonal variation (wet: May–June; dry: July–August) in activity budgets was determined using chi-square statistics and non-parametric correlation coefficients. Changes in rainfall associated with the wet–dry season transition were analyzed by correlating rainfall frequency with Julian date. All habitat data were entered first into a two-dimensional Non-metric Multidimensional Scaling (NMS) ordination plot using PRIMER 5.1 (PRIMER-E Ltd., 2001) to assess the spatial relationships among the habitat variables we measured, grouped by class. We square-root transformed our raw habitat data prior to analysis. We calculated the similarity matrix for the NMS by applying the Bray-Curtis distance on this transformed habitat dataset. We saved the ordination

scores for each axis produced by the NMS (two axes). We then applied separate Spearman’s rho correlations to determine which habitat variables correlated with those axes. Each axis was labeled according to the variable(s) that correlated most strongly (.60.7) with its NMS scores. The significance of the relationships between basilisk classes and our habitat measures was analyzed with Kruskal-Wallis H tests. We completed all analyses aside from NMS within the statistical program SPSS ver. 13.0 (SPSS Inc., Chicago, IL), with a significance level set at a 5 0.05. RESULTS Morphology.—Clear divisions in morphological characteristics were observed between juvenile, adult female, and adult male basilisks (Table 1). All morphological variables significantly correlated with SVL (log-log regressions, R2 . 0.72, P , 0.03 for all cases). Separate ANOVAs on residuals from these regressions revealed size-independent differences between all three classes in mass only (F2,26 5 9.155, P 5 0.001). Male lizards weighed the most for any particular body size (log-log regression, mass 5 3.2143 3 SVL–4.8929, R2 5 0.93). Habitat use.—Both height (Kruskal-Wallis x2 5 13.5, df 5 2, P 5 0.001) and diameter (x2 5 8.2, df 5 2, P 5 0.016) of sleep perches differed significantly among juveniles and adult female and male lizards. Adult lizards used larger perches overall, with male lizards perching on the highest and widest branches (Fig. 1A, 1B, respectively). We observed clear habitat use differences among juvenile and adult basilisks (Fig. 2). In particular, variation occurred among habitat variables correlating with two primary axes of variation: habitat structure (axis 1: PERCH, DFT) and canopy cover (axis 2: PSUN, PGRAS, DNO). Microhabitat use variation was primarily influenced by perch density, grass, and canopy cover (PERCH: x2 5 26.09, P , 0.001; PGRAS: x2 5 23.503, P , 0.001; PSUN: x2 5 17.31, P , 0.001), with juveniles occupying more open, grassier habitats than either males or females (Fig. 2). Daytime perch heights of all basilisks were similar in height and diameter despite differences in habitat-specific perch availability (x2 5 3.69, df 5 2, P 5 0.158). Macrohabitat use variation among basilisks was largely driven by proximity to overstory trees (x2 5 13.3, df 5 2, P 5 0.001), but distance to water sources (DWS: x2 5 8.27, df 5 2, P 5 0.016), human disturbances (DHD: x2 5 11.01, df 5 2, P 5 0.004), and understory trees (DNU: x2 5 6.07, df 5 2, P 5 0.048) also differed among adults and juveniles. In particular, juvenile lizards were

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Fig. 2. Results of a two-dimensional non-metric multidimensional scaling plot of the relationships between juvenile, adult male, and adult female emerald basilisk (Basiliscus plumifrons) activity budgets, with class designation as a grouping factor. Distances for each value were calculated using an untransformed Bray-Curtis similarity index. Symbols are filled by class: juvenile (white), adult female (light gray), or adult male (dark gray). Axis arrow labels and directions are based on Spearman’s rank-correlations of habitat variables recorded (see Materials and Methods), and only variables with correlation coefficients greater than 0.7 were considered in the labels for each axis. Habitat structure (axis 1) refers to increasing perch density and decreasing distance to fallen trees. Canopy cover (axis 2) refers to decreasing availability of percent sunlight, distance to overstory trees, and grass cover.

Fig. 1. Relationships between body size (snout–vent length) and sleeping perch (A) height and (B) diameter of each captured emerald basilisk (Basiliscus plumifrons) lizard during night surveys. Symbols are by class designation: juvenile, adult female, or adult male. Data are logtransformed.

found most frequently in open-canopy areas closer to water sources (Fig. 2). These use differences were also clear at the regional scale (x2 5 11.2, df 5 2, P 5 0.004). Adult male and female basilisks were each more frequently encountered in Forest Interior areas than juveniles (males: x2 5 6, df 5 2, P 5 0.05; females: x2 5 12.9, df 5 2, P 5 0.002). Juveniles were nearly always encountered in either the Field or Lagoon areas of the property (x2 5 11.2, df 5 4, P 5 0.024). Basilisk encounter frequencies varied with respect to prevailing environmental conditions, but only in the afternoon (morning: x2 5 7.5, df 5 3, P 5 0.058; afternoon: x2 5 32.5, df 5 3, P , 0.001). Over the entire day (morning and afternoon combined), we encountered most basilisks on sunny or fully overcast days (Fig. 3). Activity budgets.—Behavioral variation was evident throughout the day among juvenile and adult female and male basilisks (F3,58 5 23.178, P , 0.001). In the morning, juveniles tended to scan for shorter durations than either male (Tukey’s HSD, P 5 0.047) or female (Tukey’s HSD, P 5 0.044) lizards. In the afternoon, all classes behaved similarly with respect to activity budgets (F1,26 5 1.859, P 5 0.184).

Juvenile and adult lizards foraged at different rates (F2,59 5 14.796, P , 0.001; Table 2). Female foraging rates were highest, and significantly different from either male or juvenile lizards individually (males: Tukey’s HSD, P , 0.001; juveniles: Tukey’s HSD, P , 0.001). Juvenile and male basilisks foraged at similar rates (Tukey’s HSD, P 5 0.335). All three classes tongue-flicked at similar rates (F2,59 5 1.853, P 5 0.166). Movement rates were also similar among the three classes (F2,59 5 0.683, P 5 0.509). As rainfall frequency declined and the region entered a dry period (associated with a negative correlation between Julian date and amount of rainfall, Spearman’s rho 5 20.257, P 5 0.04), adult lizard activity shifted from peaking largely mid-morning and mid-afternoon to earlier and later peaks during these periods, respectively (x2 5 35.583, P , 0.001). Overall levels of activity of adults did not change (x2 5 2.85, P 5 0.42). In contrast, juvenile activity declined overall (Spearman’s rho 5 20.416, P 5 0.007). DISCUSSION Basiliscus plumifrons lizards were most frequently encountered near either lagoon or forested regions at El Zota station. Size differences among the classes were clear and partly due to the greater observed mass per body size exhibited by male lizards. The large body size of adult lizards (see Table 1) certainly favors historical records of their propensity to also eat smaller lizards, including juvenile basilisks (Hirth, 1963). Unfortunately we observed little interaction among juveniles and adult males or females in the current study, and zero instances of intraspecific predation. Furthermore, juvenile and adult basilisks did not significantly overlap in habitat use. We believe it unlikely that this observation was due to a

Lattanzio and LaDuke—Basilisk activity budgets and habitat use

Fig. 3. Summary of encounter frequencies for all emerald basilisk (Basiliscus plumifrons) lizards observed during this study in the morning (light gray bars) and afternoon (dark gray bars), grouped by the environmental conditions present when they were encountered (sunny, partly cloudy, mostly cloudy, or overcast). Encounter frequencies are normalized by the number of days each condition was present by dividing the number of lizards observed during a particular condition by the number of days during the study those conditions were present.

detection bias for juveniles or adults in their respective habitats. Both observers have multiple years of experience identifying tropical lizards at El Zota (MSL: 2 years; TCL: .10 years), and all habitat regions were surveyed extensively. Differences in adult and juvenile habitats were largely characterized by structural and canopy-level variation (DNO, DFT, PGRAS, and PSUN) and proximity to water (DWS). Juvenile lizards were frequently encountered in open-canopy habitats, whereas adult lizards were mostly observed within secondary forest. Both male (7.4 6 3.2 m) and female (10.3 6 2.4 m) basilisks maintained similar average distances from water sources at El Zota. These findings are similar to those reported by Vaughan and colleagues (2007) for basilisks at a cacao plantation. Juveniles in contrast averaged only 2 6 1.3 m from water sources, with most individuals encountered within 2.5 m of water. Basilisks are well known for their ability to escape predators by running on water, but this behavior is best accomplished by juveniles because larger individuals are more likely to splash and sink while running (Hsieh and

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Lauder, 2004). Juvenile lizards may therefore remain near water to take advantage of that water-running ability. Adult lizards farther from water may instead rely on other forms of predator avoidance, including running on branches or taking advantage of their cryptic coloration (green coloration and leaf-like crests in males, see Savage, 2002). Juvenile basilisks may also frequent different regions than adults to avoid competing with them or to decrease their risk of predation (Stamps, 1983). Habitats at El Zota differed in structural characteristics, including perch availability. Perch use during the day was similar among the classes even though juveniles may be expected to perform better on smaller perches (Irschick et al., 2005). We only observed perch-use differences at night, when juvenile basilisks were found sleeping on smaller perches than adult females or males (Fig. 1A, 1B). Given our dataset it is difficult to tease apart these explanations for the observed habitat-use differences because to juvenile lizards, adult basilisks can be both predators (Hirth, 1963; Greene et al., 1978) and potential competitors. The adult basilisks we observed averaged approximately three times as large as the average juvenile (see Table 1). Of the five juvenile–adult encounters we did directly observe, the smaller lizard was always chased off its perch by the larger lizard. Despite clear juvenile and adult habitat-use differences, all basilisks scanned, tongue-flicked, and moved at similar rates. Most individual lizards spent more than 60% of their time engaged in scanning behaviors. These behaviors serve multiple functions (Watters, 2009), allowing basilisks to simultaneously search for prey and scan for predators or competitors from a central perch. This broad functionality makes it difficult to pinpoint which function(s) it serves at any one time. Rates of tongue-flicking and movement were also similar among all classes. Basilisks were observed foraging somewhat infrequently, but overall adult females foraged more often than either males or juveniles. Similar sex differences in foraging rate may be tied to the reproductive cycle of adult female lizards (i.e., egg production: Parmelee and Guyer, 1995). Basilisk lizards breed yearround in Costa Rica (Savage, 2002), and thus adult females may sustain higher energetic demands than adult male or juvenile lizards. Climatic variation appeared to have little effect on basilisk encounter frequencies initially because these frequencies were similar across sunny and overcast days (morning and afternoon, see Fig. 3). Only in the afternoon were overall

Table 2. Activity Budgets of Emerald Basilisk (Basiliscus plumifrons) Lizards Encountered during Daily Surveys at El Zota Station in Northeast Costa Rica. Lizards are grouped by class designation (juvenile or adult female or male). Values are reported as mean (range).

Measurement

Males (n = 18)

Females (n = 23)

Juveniles (n = 21) 0.06 (0–0.3) 0.01 (0–0.07)

Foraging Tongue-flick rate (/min) Foraging rate (/min)

0.04 (0–0.76) 0.01 (0–0.1)

0.05 (0–0.2) 0.03 (0–0.3)

Movement Movement rate (/min) Movement duration (s) Time spent moving (%)

0.08 (0–0.63) 2.31 (0–17.78) 0.63 (0–4.94)

0.11 (0–0.33) 3.24 (0–42) 0.97 (0–7)

Scanning Time spent scanning (%) Scan duration (s)

71.4 (12.4–99.6) 258.9 (48.6–834.3)

62 (12.4–99.9) 262.35 (111.6–899.1)

0.1 (0–0.73) 3.1 (0–151.2) 1.5 (0–13.3) 60.1 (5.1–99.3) 144.72 (81.69–1776.6)

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encounter frequencies different (see Results, P , 0.001), with fewer lizards encountered during mostly cloudy conditions than expected by chance alone. Cloudy and overcast conditions are frequent at El Zota and are typical on wet season mornings, potentially inflating the likelihood of encountering a lizard in those conditions. Regardless, we observed basilisks active under all conditions (except steady rain) at the field site during the wet season. As the area entered a dry season, we encountered fewer basilisks per day. This transition was marked by a decrease in rainfall frequency but also a concomitant mid-day increase in ambient temperatures and desiccation of much of the open-canopy and edge-area vegetation. During this transition adult basilisks shifted the times they were active to earlier in the morning and later in the afternoon. Their overall frequencies of scanning, movement, and foraging behaviors did not change. Because adult lizards have established territories, they may still have to remain active in the dry season to maintain those territories (Rose, 1981). Adults may also have more access to refuges in the structurally complex secondary forest areas they frequented (e.g., Martı´n and Lo´ pez, 1995). On the other hand, juvenile lizards in more-open canopy areas were less active overall regardless of time of day. Mark–recapture estimates indicate that juvenile lizards do exhibit similar home range sizes as adults during the summer (Goldfarb, 2004), but it is unknown whether or not juveniles patrol and defend these territories year-round. If not, it may be that juvenile lizards dispersed out of our study area into other regions within or outside of El Zota in response to the drier and hotter conditions. Long-term monitoring of lizard movements throughout ontogeny would be valuable in this respect. In summary, our work provides new insight into some of the parameters that shape the activity budgets of emerald basilisk lizards. Habitat-wise, adult and juvenile lizards occupied different regions varying in degree of structural and canopy cover. Juveniles, those most effective at the species’ water-running ability due to their small body size (Hsieh and Lauder, 2004), were also frequently encountered in areas closer to water than adult lizards. By utilizing moreopen canopy lagoon areas, juveniles may be avoiding competition with or predation by adult basilisks, but we cannot rule out body size and water-running capability as additional drivers of both classes’ habitat use. Overall basilisk activity was similar in all regions and the majority of all classes’ time was dedicated to scanning, likely to search for prey or detect potential predators. Female lizards foraged more often than males or juveniles which may be due to the energetic demands of females during the reproductive season. Overall, basilisks moved rarely during observation periods. Behavioral patterns differed among adults (maintained activity but changed timing of peak activity) and juveniles (less active overall) as the area transitioned between a wet and a dry season. Our findings demonstrate the importance of considering climatic and ontogenetic variation in long-term studies of lizard activity. ACKNOWLEDGMENTS This manuscript represents a portion of a thesis submitted in partial fulfillment of the degree of Master of Biology to the Graduate School of East Stroudsburg University, East Stroudsburg, Pennsylvania by MSL. We are grateful to J. Huffman and T. Master for serving on the thesis committee

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