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Salmon et al 1995 Behavior of loggerhead sea turtles on an urban beach. II Hatchling orientationSociety for the Study of Amphibians and Reptiles Behavior of Loggerhead Sea Turtles on an Urban Beach. II. Hatchling Orientation Author(s): Michael Salmon, Melissa Garro Tolbert, Danielle Pender Painter, Matthew Goff and Raymond Reiners Source: Journal of Herpetology, Vol. 29, No. 4 (Dec., 1995), pp. 568-576 Published by: Society for the Study of Amphibians and Reptiles Stable URL: http://www.jstor.org/stable/1564740 . Accessed: 03/06/2014 10:01 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . 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 This content downloaded from 164.51.49.151 on Tue, 3 Jun 2014 10:01:45 AM All use subject to JSTOR Terms and Conditions Journal of Herpetology, Vol. 29, No. 4, pp. 568-576, 1995 Copyright 1995 Society for the Study of Amphibians and Reptiles Behavior of Loggerhead Sea Turtles on an Urban Beach. II. Hatchling Orientation MICHAEL SALMON, MELISSA GARRO TOLBERT, DANIELLE PENDER PAINTER, MATTHEW GOFF, AND RAYMOND REINERS Department of Biological Sciences, Florida Atlantic University, Box 3091, Boca Raton, Florida 33431-0991, USA ABSTRACT.- At several locations on an urban nesting beach, loggerhead hatchlings emerging from their nests did not orient toward the sea. The cause was city lighting which disrupted normal seafinding behavior. Observations and experiments were conducted to determine why females nested where hatchlings were exposed to illumination, and how hatchlings responded to local conditions. In some cases, females nested late at night after lights were turned off, but hatchlings emerged earlier in the evening when lights were on. In other cases, the beach was shadowed by buildings directly behind the nest, but was exposed to lights from gaps between adjacent buildings. In laboratory tests, "urban silhouettes" (mimicking buildings with light gaps) failed to provide adequate cues for hatchling orientation whereas natural silhouettes (those without light gaps) did. Adding a low light barrier (simulating a dune or dense vegetation) in front of the gaps improved orientation accuracy. The data show that hatchling orientation is a sensitive assay of beach lighting conditions, and that light barriers can make urban beaches safer for emerging hatchlings. At urban beaches where it may be impossible to shield all luminaires, light barriers may be an effective method for protecting turtles. At an urban beach (Boca Raton, Florida), log- gerhead turtles (Caretta caretta) deposit most of their nests in front of high condominiums and tall stands of Australian Pine trees. These ob- jects are positioned between the beach and the city and act as light barriers. In this study, we examine the consequences of these nesting preferences for the hatchlings, with emphasis upon their ability to locate the sea from the nest. Even though females at Boca Raton select nest sites (Salmon et al., 1995), managers report that some hatchlings are attracted to city lights and fail to reach the ocean. On undeveloped beach- es most females place nests where their off- spring can locate the sea. If on urban beaches females cannot select safe sites, we need to know why. One possibility is that urban ecological conditions are unique and do not provide re- liable cues to females. Another possibility is that the behavioral mechanisms used by fe- males to select appropriate nesting sites do not function normally in an urban setting. To our knowledge, no studies have focused upon these issues. Hatchlings crawl toward the sea within sec- onds after they leave their nest chamber. This behavior ("seafinding") requires an ability to orient accurately. Loggerhead hatchlings usu- ally emerge from their nests at night (Wither- ington et al., 1990). Hatchlings can find the sea by using two visual mechanisms: a positive pho- totaxis (crawling toward the more intensely il- luminated seaward horizon; Mrosovsky, 1972) and a response to differences in horizon ele- vation (hatchlings crawl away from high sil- houettes produced by trees, dunes and other objects behind the nest, and toward the lower beach horizon; Limpus, 1971). In cue conflict experiments (Able, 1993), hatchlings favored horizon elevation cues over light intensity cues (Limpus, 1971; Salmon et al., 1992). Seafinding might be disrupted at urban lo- cations for two reasons. First, bright lights cause hatchlings either to crawl in circuitous, non- directed paths ("disorientation") or to orient toward the light source itself ("misorientation"; Verheijen, 1985). Second, horizon cues differ from those on undeveloped beaches where the dune and/or its associated vegetation shows relatively little variation around a mean ele- vation. The silhouette is therefore smooth and usually extends continuously down the length of the beach. In contrast, an urban skyline pre- sents a silhouette which is irregular in eleva- tion. At Boca Raton, Australian pine trees tower above lower sea grape bushes in city parks, and buildings of different height are separated from one another by distinct low gaps (Fig. 4; Salmon et al., 1995). In laboratory tests, hatchlings ori- ented away from natural silhouettes (Salmon et al., 1992) but their response to irregular, incom- plete "urban" silhouettes has not been studied. In this study, two questions were primary. (1) Are females at Boca Raton placing nests in lo- cations where their offspring can orient nor- mally? If not, why not? (2) When hatchlings are unable to orient normally, what are the reasons? To answer these questions, we looked for cor- This content downloaded from 164.51.49.151 on Tue, 3 Jun 2014 10:01:45 AM All use subject to JSTOR Terms and Conditions HATCHLING ORIENTATION relations between where females placed nests, local lighting conditions, and how hatchlings behaved. We also conducted laboratory exper- iments in an arena which allowed us to expose hatchlings to simulated urban horizons. MATERIALS AND METHODS The study site was a 7.32 km section of beach, bordered to the North by the village of High- land Beach and to the South by the Broward/ Palm Beach County line (Fig. 1). The area is described in Salmon et al. (1995). All observa- tions and experiments were carried out be- tween July and October, 1991 and 1992. Hatchlings. -Turtles were obtained from marked nests in the afternoon of the day they would naturally emerge. From 20 to 40 hatch- lings were removed without disturbing the re- mainder of the clutch. Captured turtles were placed in a covered styrofoam box and taken by car within 10 min to our laboratory. They were stored in a dark room at outdoor temperatures until used for experiments that evening. Hatch- lings were released at a dark beach immediately after testing. Field Experiments.--Boxes with hatchlings were taken to the beach after dark. They were opened on location to expose the turtles to ambient light and cooler evening temperatures which in- duced crawling activity. Turtles were placed, either singly or in pairs, in a shallow (1-3 cm deep) pit located in the center of a 4 m diameter circle ("beach arena") drawn on a smoothed, leveled sand surface. Most turtles immediately left the pit and began crawling toward the pe- riphery. As each turtle crossed the arena bound- ary, it was captured and released. The tracks hatchlings left in the sand were traced. A few (<5%) of the turtles failed to exit the pit within 2 min and were excluded from our analysis. Orientation angle (arena center to the bound- ary exit point) was measured with a fluxgate ("Datascope") compass. Standard techniques (described in Zar, 1994) were used to calculate a mean angle and r-vector for each experiment. From the center of the arena, we measured the following: (1) distance (in m) to the spring high tide strand line; (2) distance to the upper margin of beach; and (3) relative light intensity (i) out to sea, (ii) reflected from the sand surface, (iii) within the center of the silhouette behind the beach at mid-elevation, and (iv) in the sky just above the silhouette. We also measured the intensity and direction of any bright lights which appeared to attract the turtles. An Optec stellar photometer was used for these measure- ments (see Salmon et al., 1995). Laboratory Experiments. -We compared the re- sponse of hatchlings to "natural" and "urban" silhouettes using a laboratory arena. This ap- FIG. 1. Locations on Boca Raton's beach where lighting interfered with seafinding behavior. Black rectangles are condominiums; hatched regions are parks; 1, Whitehall South; 2, Stratford Arms; 3, Clois- ter del Mar/South Inlet Park; 4, Sable Point; 5, Boca Mar; 6, Pavilion, South Beach Park; 7, Pavilion, Red Reef Park; 8, Ocean View/Lake View; 9, San Remo; 10, Spanish River Park. paratus, the procedures used to produce silhou- ettes, and the techniques employed to measure light intensity and hatchling orientation, have been described previously (Salmon et al., 1992). Here, we give a brief summary. The arena was circular (1.09 m, I.D.) and housed in a light-tight, windowless room. Hatchlings were tested individually. Each turtle was tied by a short (5.0 cm) line to the center of the arena. Tethered hatchlings could crawl in any direction, but made no forward progress. 569 This content downloaded from 164.51.49.151 on Tue, 3 Jun 2014 10:01:45 AM All use subject to JSTOR Terms and Conditions M. SALMON ET AL. The platform upon which they crawled was rough plywood, painted flat black. The interior of the arena was lined with a translucent white styrene screen from floor lev- el to an elevation 34? above the turtle. One half of the arena screen was back illuminated by fluorescent tubes while the opposite half was dark. Light intensities were measured at mid- screen elevation from the center of the illu- minated and dark sides before any silhouettes were placed on the screen. All such measure- ments were made with the Optec photometer elevated on a stand and positioned in the center of the arena. The light tubes and back surface of the screen were covered with #94 Roscolux filter sheeting. Light wavelengths were confined to 420-620 nm, with maximum transmission (74%) at 520 nm (detected with greatest sensitivity by dark adapted juvenile green turtles; Granda and O'Shea, 1972). Stimulus Simulations. To mimic the outline of buildings near the beach, we cut shapes (20? wide by 15? high) out of thick black paper and fixed them with clear tape to the illuminated ("city") side of the screen. All such objects were presented as they would appear to a hatchling on the beach: projecting from the arena floor upward. Shape and horizontal extent were mea- sured from the position of a tethered hatchling. In separate experiments, turtles were presented with urban silhouettes which differed in: (1) shape (curved or rectangular), (2) horizontal ex- tent (40?-100?), (3) the number of light "gaps" (2-4, each 20? wide), and (4) the presence or absence of a lower, solid silhouette simulating dune or vegetation. Control tests assayed the responses of hatchlings to light intensity dif- ferences used in other tests, and to a natural silhouette placed against the illuminated side of the arena. This silhouette contained no light gaps, was 16? high at the center, 180? in width, and sloped symmetrically down to the platform on each side of center. The shape mimicked the appearance of low vegetation growing behind the beach. Because the purpose in these experiments was to determine how hatchlings responded to ur- ban and natural silhouettes, we deliberately avoided presenting light intensities which were especially bright (such as those measured at city beaches; levels reported in Salmon et al., 1995). We assumed if turtles responded differently to the two categories of silhouettes when light lev- els were modest, such differences would be magnified at higher levels of illumination. Hatchling Orientation.-After they were placed in the arena, hatchlings immediately began crawling. Within a one min acclimation period, they usually chose a course. At the end of the acclimation period, each turtle's orientation (di- rection of its long body axis relative to a gauge on top of the arena) was recorded every 15 sec until ten bearings were obtained. These data were used to estimate a mean angle and r-vector for each turtle. Hotelling tests were used to de- termine a second order group mean angle and r-vector for each experiment. RESULTS Variation in Performance: Disorientation.-At many beach locations, seafinding behavior was normal. However at others, scattered through- out the study site, seafinding was disrupted (Fig. 1). Normal orientation was shown at some lo- cations in South Beach and Red Reef Parks (Fig. 2) where tall Australian pine trees formed a high, solid light barrier behind the beach. Un- der these conditions, hatchlings crawled on straight paths toward the ocean. Disorientation occurred where barriers were lower and/or in- complete, allowing diffuse light from many street lights in the park and bordering the ocean highway to illuminate the beach. Severity of disorientation varied (Fig. 2). When perfor- mance was mildly affected, paths were straight but vectors shown by individual turtles di- verged (Ocean View/Lake View; Fig. 2). When performance was strongly compromised paths showed occasional "loops," crawl directions changed frequently, and individual turtles ex- ited the arena in various directions (San Remo, Spanish River Park; Fig. 2, bottom). Misorientation: Temporal Effects.-Misorienta- tion occurred when turtles were exposed to dis- crete, obviously bright light sources from one or occasionally, two directions. For example at Red Reef park, a pavilion light behind the beach remained on until midnight. While it was on, turtles were attracted west toward the source; after a timer switched the light off, they crawled east toward the ocean (Fig. 3A, B). Lights in condominiums also attracted tur- tles. While exposed to an apartment light from one building and a garage light from another, most (7 of 10) of the turtles crawled away from the ocean toward the buildings (Fig. 3C). After the apartment light was extinguished, most hatchlings oriented toward the sea (Fig. 3D) but the garage light attracted one turtle and may have been responsible for the abnormal crawl tracks shown by two others. Spatial Effects.-The effect of beach lighting depended upon the exact location of the arena. Near a condominium (Boca Mar), stairway and porch lights illuminated a patch of beach (Fig. 4A) north of the building. When tests were con- ducted within the illuminated beach, most tur- tles crawled to the sea but their paths often were 570 This content downloaded from 164.51.49.151 on Tue, 3 Jun 2014 10:01:45 AM All use subject to JSTOR Terms and Conditions HATCHLING ORIENTATION South Beach 0 Red Reef Park Ocean View/Lake View Sable Point San Remo Spanish River Park FIG. 2. Paths of hatchlings shown during beach arena experiments (N = 20 turtles per test). Seafinding accuracy varies with location at Boca Raton's beaches. At some areas of South Beach and Red Reef Parks, seafinding is normal. Disruption is moderate at Ocean View/Lake View and at Sable Point. Lights seriously interfere with orientation at San Remo and Spanish River Park. 0? = North; 90? = East (direction to the ocean). looped and sinuous (Fig. 4, lower left). A sig- nificant minority crawled south instead of east. Tests done 30 m to the south (B), where the building was dark, yielded normal orientation (Fig. 4, lower right). Similar spatial effects also were evident at other locations. Outside hallway lights from a tall condominium (Cloister del Mar) illuminat- ed the southern half of South Inlet Park (Fig. 5). Experiments were carried out at three park locations (a, b, c) varying in distance from these lights. Seafinding performance was affected at all three sites (mean headings were south of east). Both scatter and the tendency to orient south increased at locations closer to the build- ing (Fig. 5A-C). Laboratory Experiments: Controls.-Hatchlings exposed to a brightness difference oriented to- ward the brighter half of the arena (Fig. 6A). A natural silhouette placed against the illuminat- ed side of the arena elicited orientation in the opposite direction (Fig. 6B). Urban Silhouettes: Horizontal Extent.-Hatch- lings held well-defined courses when present- ed with rectangular shapes simulating dark buildings (Fig. 6C-E). But as groups turtles showed more scatter in orientation when pre- sented with narrower horizontal extents (40? or 60?; Fig. 6C, D) than when exposed to a wider horizontal extent (100?; Fig. 6E). Effect of Light Gaps.-When silhouettes con- tained either 3 or 5 rectangular shapes, group orientation could not be distinguished from random (Fig. 7A-B). Effect of Light Gaps and Silhouette Shape.-When presented with curved, symmetrical silhouettes containing light gaps, group orientation was bimodal (most turtles crawled about 45? to the left or to the right of a heading directly away from the silhouette; Fig. 7C). Addition of a Low Light Barrier.-The addition of a low (8? high at center) horizon, simulating the appearance of a dune or vegetation in front of the light gaps, resulted in improved orien- tation (compare dispersion [r-vectors] in Figs. 7B to 7D, and 7C to 7E). DISCUSSION At Boca Raton, females position nests where some hatchlings are exposed to city lights. Lights interfere with normal seafinding behavior. Be- havioral interference takes the form of either 571 This content downloaded from 164.51.49.151 on Tue, 3 Jun 2014 10:01:45 AM All use subject to JSTOR Terms and Conditions M. SALMON ET AL. Pavilion: Red Reef Park B. Lights off Ocean N N 20 8 r - 0.84 5. a -i12 E E Stratford Arms D. Lights Off FIG. 3. Temporal interference from lights which are turned on for portions of the dark cycle. A, when a pavilion light is on (heavy line outside circle) hatch- lings crawl toward it (west) and away from the ocean; B, after the light is switched off, they crawl east. C, an apartment light at Stratford Arms (left of circle) and a garage light from an adjacent building (above circle) disrupt seafinding; after the apartment light is extinguished (D), most turtles crawl toward the sea. disorientation or misorientation depending upon local conditions. Laboratory experiments indicate that urban silhouettes provide inade- quate cues for orientation. Photic Ecology and Nest Site Selection.-On de- veloped beaches, the presence of artificial lights is inversely correlated with nesting activity by sea turtles (Worth and Smith, 1976; Mortimer, 1982; Proffitt et al., 1986), and is correlated pos- itively with interference in normal Seafinding behavior (Mann, 1978; Raymond, 1984). With- erington (1992) provided direct evidence that lights alone (separated from other kinds human interference) can reduce nesting activity on otherwise attractive rookery beaches. Boca Raton differs from most moderately sized metropolitan areas in South Florida because its beaches are relatively dark and attract substan- tial numbers of nesting turtles. The shoreline is dominated by city parks and condominiums (Fig. 1). At the parks, light levels at night are reduced compared to beaches bordered by pri- vate residences or beach hotels. Park vegetation in many locations acts as an effective light bar- rier; however in other locations, the barrier is incomplete (Fig. 2). Condominiums also act as barriers whose effectiveness varies with loca- tion and time. During June and July, when log- FIG. 4. Spatial interference from lights which are present at some portions of the beach but not in ad- jacent areas. Upper: a patch of beach immediately north of Boca Mar is exposed to stairway and porch lights. When tested in the patch (A and lower left), some hatchlings show irregular paths while others orient south (between the ocean and the light source) instead of east. In front of the building where it is dark (B and lower right), seafinding is normal. gerhead nesting reaches its peak, most condo- minium apartments are unoccupied. Buildings are relatively dark and can act as light barriers. However, sometimes a few apartment lights are left on. The staff usually keep lobby and garage lights on as well. Given that beaches are generally shielded from direct city lighting, and that females nest in the darkest available locations, why are hatchlings still affected by city lights? Part of the answer is related to differences between turtle and human activity patterns. Most hu- mans turn off lights before midnight whereas female loggerheads nest throughout the night (Dodd, 1988) and make nesting "decisions" based upon immediate conditions. Thus a fe- male may deposit her eggs on a beach after midnight, when lights are off, but her hatch- lings may emerge earlier in the evening, when lights are on. In fact, most loggerhead hatch- lings emerge from nests between dusk and mid- night (Witherington et al., 1990) when the probability of exposure to lights is much higher. No selective force in the evolutionary history of sea turtles prepares either a nesting female or her offspring for these unique ecological cir- cumstances. The spatial distribution of human light sources also presents a novel problem for females and their offspring. At Boca Raton, females prefer A. Lights on Boca Mar N r - 0.82 aI268 C. Lights on N LE North Side In Front 572 I This content downloaded from 164.51.49.151 on Tue, 3 Jun 2014 10:01:45 AM All use subject to JSTOR Terms and Conditions HATCHLING ORIENTATION Cloister del Mar and South Inlet Park N South Q Inlet Park I UV\\ B. A. Brightness Difference B. Natural Silhouette Bright A. 90 E Dim C. Two Blocks C. D. Three Blocks E. Five Blocks FIG. 5. Spatial interference. Above, left: stairway lights from Cloister del Mar (shaded) expose the southern portions of South Inlet Park to light. The effect on hatchling orientation varies with distance from the building. At the park center (A), hatchlings orient slightly south of a heading directly toward the ocean. The tendency to crawl south, as well as group dispersion, increases as the test site is moved closer to the building (and its lights; B and C). to nest in front of objects that darken the beach. They pay little attention to lights which illu- minate the beach farther away (such as the spac- es between buildings, or breaks in the vegeta- tion barrier located at a distance). On ancient nesting beaches, such a perceptual strategy probably had few adverse effects because at- tractive features viewed directly ahead were re- liable indicators of conditions in adjacent areas. But on urban beaches, there may be abrupt dif- ferences in lighting conditions over distances of a few meters (Figs. 4 and 5). Such spatial variation compromises the ability of females to select safe sites on the basis of the view directly ahead. Additional evidence for this "straight ahead" mode of nest site selection was provided by Witherington (1992). He exposed a normally dark rookery site (Melbourne Beach) to artificial lights. During exposure, loggerhead nesting in the illuminated areas was reduced whereas nesting densities in the control (dark) sites im- mediately adjacent to the lighted beach re- mained high. In fact, nesting densities in the FIG. 6. Laboratory arena experiments. One side (upper half in each circle) of the arena is illuminated to simulate city lighting; the other side is darker. In control tests, hatchlings are exposed to a difference in light intensity (A), and to a natural silhouette placed against the illuminated screen (B). Turtles orient to- ward the brighter horizon and away from the sil- houette (as they would on natural beaches). When presented with silhouettes of buildings varying in horizontal extent (C = 40?, D = 60?, E = 100?; elevation is 15? in all cases), hatchlings are well oriented only from the widest silhouette (E). Arrow outside each circle shows group mean angle (a). plots bordering the illuminated beach were as high as those located farther away from the lighted area. The problem would be far less serious if hatchlings also made orientation decisions based upon stimulus conditions confined to a land- sea axis. Unfortunately, seafinding orientation is probably based upon the entire visual field located at or near the horizon (Verheijen and Wildschut, 1973; Mrosovsky and Kingsmill, 1985). Such a perceptual strategy means that lighting conditions down the beach, which their mothers ignore, will influence hatchling ori- entation behavior. Hatchling Behavior.-Responses of hatchlings to city lighting varied, depending upon loca- tion. Disorientation, or the inability to crawl in 573 This content downloaded from 164.51.49.151 on Tue, 3 Jun 2014 10:01:45 AM All use subject to JSTOR Terms and Conditions M. SALMON ET AL. A. Three Blocks B. Five Blocks N=18 a = 232? r=0.01 C. Horizon: Five Blocks D. Blocks with Horizon E. Filled Horizon FIG. 7. Laboratory arena experiments. Effect of 20? wide light gaps on turtle orientation. Hatchlings show group orientation indistinguishable from random when presented with two (A) or four (B) light gaps (each separated by 20? wide x 15? high blocks). When gaps of the same width occur in a natural (curved) silhouette (C), orientation improves but many turtles deviate to the left or right of a course away from the silhouette. Addition of a low (8? high at center) light barrier (7D, 7E) improves orientation (compare to 7B and 7C, respectively). consistent directions, occurred in front of city parks (Spanish River), buildings behind city parks (San Remo), or exposed buildings (Sable Point) where vegetation barriers were low and incomplete (Fig. 2). At Spanish River Park, for example, several lights in the park and parallel to the ocean highway were visible from the beach. They weakly illuminated the entire area from behind, as well as down the length of, the beach. We observed misorientation responses when hatchlings were exposed to much brighter, dis- crete lights sources which reached the beach from one or two directions. These elicited re- sponses which ranged from an attraction to the light sources (Fig. 3), to headings on courses between those lights and the sea (Figs. 4 and 5). The data suggest that misorientation in ur- ban areas may represent the outcome of a bal- ance between competing stimuli: those (like dif- ferences in horizon elevation) which turtles use to locate the sea, and those (such as bright light sources) which attract hatchlings in other di- rections. In our laboratory experiments, we examined how hatchlings responded to natural and urban silhouettes similar to those at Boca Raton's beaches. Our results suggest that hatchlings are sensitive to both the horizontal extent and the vertical outline (silhouette) of objects, confirm- ing that form vision is probably important in seafinding (van Rhijn, 1979; van Rhijn and van Gorkum, 1983). Complete, dark silhouettes such as those which occur behind natural beaches are effective at directing turtles on "seaward" courses. However, "incomplete" silhouettes with gaps, outlined against a background of city glow, fail to provide adequate elevation cues for hatchling orientation. Dune removal, as well as the clearing of vegetation between buildings and the sea, is a common practice at Boca Raton and many other urban areas. These modifica- tions have the effect of exaggerating the irreg- ular appearance of urban silhouettes. Management Implications.-Boca Raton's nest- ing beach must be viewed as a successful ex- periment, at least compared to adjacent urban regions. The relatively dark beaches at Boca Ra- ton serve as sites for an average of 99 nests/km. In Broward County, just to the south of Boca Raton, light levels on the beach are higher and nest densities are lower (Burney and Mattison, unpubl. data). Most nests deposited there must be moved to a localized hatchery because if left in situ, light would prevent hatchlings from reaching the sea. The costs to the turtles (in loss of attractive nesting habitat, in egg death as a consequence of "relocation", and in vulnera- bility to predators and to storms which can de- stroy a localized hatchery), as well as to humans (in management time and money), are very high. A key component of Boca Raton's manage- ment program is light shielding. However, problems still exist. Most of the existing beach lighting problems occur because neither the city parks nor the condominiums are complete light barriers. Gaps in park vegetation, and lights from building lobbies, garages, and (occasion- ally) apartments, still illuminate the beach. Cur- rent lighting regulations emphasize the reduc- tion of beach front lighting. At urban nesting beaches managers must place additional em- phasis upon light sources between buildings, which do not directly face the ocean (stairways, hallways, pools, and walkways). If local light- ing regulations included such areas, many but not all of the problems could be reduced or eliminated. At nesting beaches where few luminaires are present, turning off or shielding lights is an effective way to reduce misorientation prob- 574 This content downloaded from 164.51.49.151 on Tue, 3 Jun 2014 10:01:45 AM All use subject to JSTOR Terms and Conditions HATCHLING ORIENTATION lems (Raymond, 1984). However, at urban beaches the glow of city lights behind the beach and the unique silhouette presented by the sky- line represent problems which existing lighting regulations can not solve. An alternative solu- tion is to couple reduction of beach lighting with re-establishment of light barriers between the beach and the city. The net effect of such a manipulation is to strengthening the influence of elevated horizons as orientation cues relative to the influence of city lighting. While these efforts can not reduce overhead city glow, they do serve to darken areas close to the horizon. Evidence from other studies suggests that hatchlings make orientation decisions based upon lighting conditions at lower elevations (Mrosovsky, 1972; Verheijen and Wildschut, 1973; Salmon et al., 1992). This perceptual char- acteristic probably explains why even low light barriers had a dramatic effect upon hatchling orientation in our arena experiments (Fig. 7). Thus, dune and vegetation restoration efforts may be a simple and effective way of protecting hatchlings from lighting problems in urban ar- eas (McFarlane, 1963). An urban management strategy, then, must involve three elements: (1) reducing or elimi- nating lights which directly impinge upon the beach; (2) modifying the silhouette behind the beach to make it more complete; and (3) assay- ing the effectiveness of these changes by mon- itoring hatchling seafinding behavior. The goal should be to provide an environment that at- tracts females and which allows their offspring to successfully reach the ocean without human intervention. Because so much baseline data are already available, Boca Raton's beaches can serve as a location for testing known protocols, as well as for developing new modifications. Such information should prove invaluable for for- mulating management plans for other urban beaches. Even at Boca Raton, nesting activity is re- duced compared to levels in less developed ar- eas where beaches are much darker. The con- tinued influx of new human residents to Flor- ida, as well as future immigration projections (Bouvier and Weller, 1992), indicate that pres- sure to develop coastal beaches will continue. This study shows that even under the best of circumstances, urban beaches are relatively un- attractive as nesting sites for loggerhead turtles. The loss of dark, undeveloped beaches along Florida's coastline poses a continuing threat for these animals, one for which there is at present no known remedy. Acknowledgments. -Supported by a coopera- tive agreement from the National Oceano- graphic and Atmospheric Administration, by Florida Atlantic University, and by personal funds. We are grateful to personnel from the Gumbo Limbo Nature Complex for their co- operation. Cathy and Ken Lohmann, as well as two journal referees, made suggestions which improved earlier drafts. Alan Huff and Jeanette Wyneken provided encouragement and moral support, for which we are most grateful. LITERATURE CITED ABLE, K. P. 1993. Orientation cues used by migratory birds: a review of cue-conflict experiments. Trends Ecol. Evol. 8:367-371. BOUVIER, L. F., AND B. WELLER. 1992. Florida in the 21st Century: The Challenge of Population Growth. Center for Immigration Studies, Washington, D.C. DODD, C. K., JR. 1988. Synopsis of biological data on the loggerhead sea turtle Caretta caretta (Linnaeus 1758). U.S. Fish Wildl. Serv., Biol. Rep. 88. GRANDA, A. M., AND P. J. O'SHEA. 1972. Spectral sensitivity of the green turtle (Chelonia mydas my- das) determined by electrical responses to heter- chromatic light. Brain, Behav. Evol. 5:143-154. LIMPUS, C. J. 1971. Sea turtle ocean finding behav- iour. Search 2:385-387. MANN, T. M. 1978. Impact of developed coastline on nesting and hatchling sea turtles in southeast- ern Florida. Florida Mar. Res. Publ. 33:53-55. MCFARLANE, R. W. 1963. Disorientation of logger- head hatchlings by artificial road lighting. Copeia 1963:153. MORTIMER, J. A. 1982. Factors affecting beach selec- tion by nesting sea turtles. In K. A. Bjorndal (ed.), Biology and Conservation of Sea Turtles, pp. 45- 51. Smithsonian Institution Press, Washington, D.C. MROSOVSKY, N. 1972. The water-finding ability of sea turtles. Behavioral studies and physiological speculations. Brain, Behav. Evol. 5:202-225. , AND S. J. KINGSMILL. 1985. How turtles find the sea. Z. Tierpsychol. 67:237-256. PROFFITT, C. E., R. E. MARTIN, R. G. ERNEST, B. J. GRAUNKE, S. E. LECROY, K. A. MULDOON, B. D. PEERY, J. R. WILCOX, AND N. WILLIAMS-WALLS. 1986. Ef- fects of power plant construction and operation on the nesting of the loggerhead sea turtle (Caretta caretta); 1971-84. Copeia 1986:813-816. RAYMOND, P. W. 1984. Sea turtle hatchling disori- entation and artificial beachfront light. A review of the problem and potential solutions. Center of Environmental Education, Washington, D.C. RHIJN, F. A. VAN. 1979. Optic orientation in hatch- lings of the sea turtle Chelonia mydas. I. Brightness: not the only optic cue in sea-finding orientation. Mar. Behav. Physiol. 6:105-121. , AND J. C. VAN GORKUM. 1983. Optic orien- tation in hatchlings of the sea turtle, Chelonia my- das. III. Sea-finding behaviour: the role of photic and visual orientation animals walking on the spot under laboratory conditions. Mar. Behav. Physiol. 9:211-218. SALMON, M., J. WYNEKEN, E. FRITZ, AND M. LUCAS. 1992. Seafinding by hatchling sea turtles: role of brightness, silhouette and beach slope as orien- tation cues. Behaviour 122:56-77. 575 This content downloaded from 164.51.49.151 on Tue, 3 Jun 2014 10:01:45 AM All use subject to JSTOR Terms and Conditions M. SALMON ET AL. M. SALMON ET AL. , R. REINERS, C. LAVIN, AND J. WYNEKEN. 1995. Behavior of loggerhead sea turtles on an urban beach. I. Correlates of nest placement. J. Herpetol. 29:560-567. VERHEIJEN, F. J. 1985. Photopollution: artificial light optic spatial control systems fail to cope with. In- cidents, causations, remedies. Exp. Biol. 44:1-18. , AND J. T. WILDSCHUT. 1973. The photic ori- entation of sea turtles during water finding be- haviour. Neth. J. Sea Res. 7:53-67. WITHERINGTON, B. E. 1992. Behavioral responses of nesting sea turtles to artificial lighting. Herpeto- logica 48:31-39. , R. REINERS, C. LAVIN, AND J. WYNEKEN. 1995. Behavior of loggerhead sea turtles on an urban beach. I. Correlates of nest placement. J. Herpetol. 29:560-567. VERHEIJEN, F. J. 1985. Photopollution: artificial light optic spatial control systems fail to cope with. In- cidents, causations, remedies. Exp. Biol. 44:1-18. , AND J. T. WILDSCHUT. 1973. The photic ori- entation of sea turtles during water finding be- haviour. Neth. J. Sea Res. 7:53-67. WITHERINGTON, B. E. 1992. Behavioral responses of nesting sea turtles to artificial lighting. Herpeto- logica 48:31-39. , K. A. BJORNDAL, AND C. M. MCCABE. 1990. Temporal pattern of nocturnal emergence of log- gerhead turtle hatchlings from natural nests. Co- peia 1990:1165-1168. WORTH, D. F., AND J. B. SMITH. 1976. Marine turtle nesting on Hutchinson Island, Florida, in 1983. Florida Mar. Res. Publ. 18:1-17. ZAR, J. H. 1984. Biostatistical analysis. Prentice-Hall, New Jersey. 718 pp. Accepted: 20 July 1995. , K. A. BJORNDAL, AND C. M. MCCABE. 1990. Temporal pattern of nocturnal emergence of log- gerhead turtle hatchlings from natural nests. Co- peia 1990:1165-1168. WORTH, D. F., AND J. B. SMITH. 1976. Marine turtle nesting on Hutchinson Island, Florida, in 1983. Florida Mar. Res. Publ. 18:1-17. ZAR, J. H. 1984. Biostatistical analysis. Prentice-Hall, New Jersey. 718 pp. Accepted: 20 July 1995. Journal of Herpetology, Vol. 29, No. 4, pp. 576-583, 1995 Copyright 1995 Society for the Study of Amphibians and Reptiles Frillneck l.izard Morphology: Comparisons between Sexes and Sites KEITH CHRISTIAN, GAVIN BEDFORD, AND ANTHONY GRIFFITHS School of Biological Sciences, Northern Territory University, Darwin, Northern Territory 0909, Australia ABSTRACT. - Large samples of frillneck lizards, Chlamydosaurus kingii, were measured from two sites approximately 150 km apart in the Northern Territory of Australia. Frill size increases linearly with SVL up to a SVL of 103 mm. At larger SVLs frill size continues to increase linearly, but with a greater slope. This inflection point corresponds to the SVL at which the gap between the two halves of the frill closes. The relationship between neck length and SVL is a simple line without an inflection point. Jaw length and head width show an allometric pattern that is similar to frill length, but the inflection point corresponds to a SVL of approximately 204 mm. The significance of this change in slope is unclear because this SVL does not correspond to any known ecological or morphological factors. Compared to females, male lizards have significantly larger frills, longer jaws, and wider heads for a given SVL. Males also have a longer frill for a given head width. Morphological differences exist between the two sites: at one site the frill length, jaw length, and dry season masses of large males are greater for a given SVL than those of large males at the other site, but at the second site the lizards of both sexes tend to have wider heads. The differences between the sexes with respect to frill and head sizes are consistent with the use of these structures for intraspecific displays, but the significance of the differences between the two sites is not known. Journal of Herpetology, Vol. 29, No. 4, pp. 576-583, 1995 Copyright 1995 Society for the Study of Amphibians and Reptiles Frillneck l.izard Morphology: Comparisons between Sexes and Sites KEITH CHRISTIAN, GAVIN BEDFORD, AND ANTHONY GRIFFITHS School of Biological Sciences, Northern Territory University, Darwin, Northern Territory 0909, Australia ABSTRACT. - Large samples of frillneck lizards, Chlamydosaurus kingii, were measured from two sites approximately 150 km apart in the Northern Territory of Australia. Frill size increases linearly with SVL up to a SVL of 103 mm. At larger SVLs frill size continues to increase linearly, but with a greater slope. This inflection point corresponds to the SVL at which the gap between the two halves of the frill closes. The relationship between neck length and SVL is a simple line without an inflection point. Jaw length and head width show an allometric pattern that is similar to frill length, but the inflection point corresponds to a SVL of approximately 204 mm. The significance of this change in slope is unclear because this SVL does not correspond to any known ecological or morphological factors. Compared to females, male lizards have significantly larger frills, longer jaws, and wider heads for a given SVL. Males also have a longer frill for a given head width. Morphological differences exist between the two sites: at one site the frill length, jaw length, and dry season masses of large males are greater for a given SVL than those of large males at the other site, but at the second site the lizards of both sexes tend to have wider heads. The differences between the sexes with respect to frill and head sizes are consistent with the use of these structures for intraspecific displays, but the significance of the differences between the two sites is not known. Of the various functions that have been sug- gested for the frill of the frillneck lizard, Chla- mydosaurus kingii, only intraspecific communi- cation and predator deterrence are supported by the evidence (Shine, 1990). Both sexes use the frill in displays, but the most frequently observed displays involve males during the breeding season (Shine, 1990; pers. obs.). Males are territorial (Shine and Lambeck, 1989), and in an initial analysis of the morphological fea- tures of this species, Shine (1990) found that males have larger heads (jaw length) than fe- males of a given SVL. This result was attributed to sexual selection for success in male combat (Shine, 1990) and is consistent with previous Of the various functions that have been sug- gested for the frill of the frillneck lizard, Chla- mydosaurus kingii, only intraspecific communi- cation and predator deterrence are supported by the evidence (Shine, 1990). Both sexes use the frill in displays, but the most frequently observed displays involve males during the breeding season (Shine, 1990; pers. obs.). Males are territorial (Shine and Lambeck, 1989), and in an initial analysis of the morphological fea- tures of this species, Shine (1990) found that males have larger heads (jaw length) than fe- males of a given SVL. This result was attributed to sexual selection for success in male combat (Shine, 1990) and is consistent with previous interpretations of sexual size dimorphism in liz- ards (Carothers, 1984; Vitt and Cooper, 1986). However, although males grow larger than fe- males, Shine's (1990) sample of lizards (N = 25) did not show sexual dimorphism with respect to the relative size of the frill. Given that the head and frill are used together in displays (Kent, 1895; pers. obs.), the result indicating sexual dimorphism for one of these structures, but not the other, is enigmatic. During the course of ecological studies of C. kingii we had the opportunity to measure a large number of individuals at two sites in the North- ern Territory of Australia. This large data set allows a more complete analysis of the mor- interpretations of sexual size dimorphism in liz- ards (Carothers, 1984; Vitt and Cooper, 1986). However, although males grow larger than fe- males, Shine's (1990) sample of lizards (N = 25) did not show sexual dimorphism with respect to the relative size of the frill. Given that the head and frill are used together in displays (Kent, 1895; pers. obs.), the result indicating sexual dimorphism for one of these structures, but not the other, is enigmatic. During the course of ecological studies of C. kingii we had the opportunity to measure a large number of individuals at two sites in the North- ern Territory of Australia. This large data set allows a more complete analysis of the mor- 576 576 This content downloaded from 164.51.49.151 on Tue, 3 Jun 2014 10:01:45 AM All use subject to JSTOR Terms and Conditions