Centro di Studio per la Faunistica ed Ecologia Tropicali del C.N.R., via Romana 17, ..... shoreline limits, where the sandhoppers normally live. The adults migrated from the ... Mediterranean beaches and differs from Atlantic pat- terns in which ...
Springer-Verlag 1997
Marine Biology (1997) 128: 63–72
F. Scapini · M. Audoglio · L. Chelazzi · I. Colombini M. Fallaci
Astronomical, landscape and climatic factors influencing oriented movements of Talitrus saltator in nature
Received: 24 September 1996 / Accepted: 25 October 1996
Abstract The present study was conducted on a Mediterranean beach (Burano, southern Tuscany, Italy) to examine the timing, orientation, and motivating and directing factors of the spontaneous movements of the sandhopper Talitrus saltator (Montagu, 1808). In April 1994, October 1994 and June 1995, during different moon phases, traps were positioned in the eulittoral zone, which intercepted sandhoppers when walking on the sand surface. At the same time environmental parameters were registered. Contemporaneously, orientation tests were carried out on active individuals using two arenas, one of which permitted a view of both sky and landscape and one which prohibited the landscape view. The results show landward migration after sunset, for juveniles later than for adults, nonoriented activity for 2 or 3 h after midnight and seawards zonal recovery before and after sunrise. The main microclimatic factor modulating activity was sand temperature, while the nonoriented activity between the two migratory movements seems to be endogenously determined. Both sky and landscape cues are used by sandhoppers for orienting their course, but the landscape view is sufficient and necessary on new moon nights. These results contribute to solution of the controversy on the mechanisms actually motivating sandhoppers in nature.
Introduction Sandhoppers, common inhabitants of sandy shores, are behaviourally adapted in the timing of activity and space Communicated by M. Sara`, Genova F. Scapini (&) · M. Audoglio Dipartimento di Biologia Animale e Genetica ‘‘Leo Pardi’’ dell’Universita` di Firenze, via Romana 17, I-50125 Florence, Italy L. Chelazzi · I. Colombini · M. Fallaci Centro di Studio per la Faunistica ed Ecologia Tropicali del C.N.R., via Romana 17, I-50125 Florence, Italy
orientation, permitting them to avoid environmental extremes. Prior trapping experiments on the beach demonstrated that Mediterranean sandhoppers migrate at night from the water’s edge to the dune base and in some cases up the dune (Geppetti and Tongiorgi 1967; Scapini et al. 1992). These results contradict observations by Williams (1983) in tidally influenced shores in Britain that sandhoppers forage at night downshore in stranded algae. Laboratory experiments under constant conditions have shown endogenously determined changes in orientation with respect to a black/white boundary and an artificial light, which may be related to migration in nature (Edwards and Naylor 1987; Mezzetti et al. 1994). This hypothesis, however, required confirmation from field experiments on the orientation responses of spontaneously active sandhoppers at night. A substantial amount of data exists on the orientation capabilities of sandhoppers for zonal recovery when passively dislocated from their burrows during the day (Papi and Pardi 1953a, b). However, it is still controversial how sandhoppers orient in nature during their spontaneous feeding migration. Apparently, contradictory hypotheses have been proposed, each supported by experimental evidence. Landscape cues, such as the silhouette of the dune on the horizon, may orient sandhoppers when they burrow in the sand above the high tide mark after the night migration (Williamson 1951; Edwards and Naylor 1987). The moon may act as astronomical reference at night (Papi 1960; Enright 1972). The slope orientation has been suggested as a possible general cue in the beach habitat (Craig 1973). Differences in celestial light intensity on the horizon may provide information on the position of the shoreline (Verheijen 1978), and the earth’s magnetic field has also been proposed as an orienting cue on new moon or cloudy nights (van den Bercken et al. 1967). Experiments using translocation to differently oriented shores or away from the seashore have shown the simultaneous use of several cues: beach slope, differences in celestial radiance over land and sea, and landscape view, all of which may enhance or interfer with solar orientation
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(Ercolini and Scapini 1974; Hartwick 1976; Ercolini et al. 1983; Ugolini et al. 1986). All these experiments were conducted during the day under stressful conditions. Therefore, the questions still remain open if, when and how sandhoppers are spontaneously oriented during their active phase. The migratory pattern observed on Mediterranean beaches, upshore at night and downshore at dawn to burrow in moist sand at the water’s edge, could be conceived of as a shift of the population due to changes in environmental gradients (temperature, humidity, salinity, etc.) or, conversely, as indirect orientation based on distant cues, such as moon, sun and/or landscape. Therefore, we examined the orientation of sandhoppers spontaneously moving in the field at night in relationship to astronomical and landscape cues and various environmental conditions. We carried out the experiments at different moon phases in order to also test the importance of this astronomical cue for orientation.
Materials and methods The study was conducted on Talitrus saltator (Montagu, 1808) at the beach in front of the Burano Lagoon (Grosseto, Italy). The trapping tests were performed in the field on 26 to 27 April 1994 (full moon), 11 to 12 October 1994 (first quarter of the moon), and 29 to 30 June 1995 (new moon). The following environmental parameters were registered simultaneously with the trapping experiments: air temperature and humidity; atmospheric pressure; wind speed and direction, using an electronic weather station; sand temperature on the surface and at 20 cm of depth, using an analog thermometer; and surface sand moisture, by comparing the wet and dry weights of each sample. Moon heights were calculated with software provided by the University of Florence. Cross-pit-fall traps were positioned on the eulittoral, which intercepted individuals from four significant directions: seaward, landward and the two longshore directions (Scapini et al. 1992). Three traps were positioned at a distance of 5 m from the shoreline, three at 10 m and three at 15 m (Fig. 1). The traps were visited each hour, and the sandhoppers counted and gathered in containers with moist sand. The captures in the traps facing the same direction (seaward, landward, longshore) were pooled for the analysis. Specimens smaller than 5 mm were registered as juveniles. Samples
of the adults were tested for orientation during the hour after capture. Two circular orientation chambers (arenas) of 40 cm of diameter with 72 pit-fall sectors of 5° each (Scapini and Pardi 1979) were positioned horizontally on the sand at 10 m from the shoreline. One of them was screened by a transparent Plexiglas cylinder which permitted full view of sky and horizon (unscreened arena); the other one had a screen of white Plexiglas, 10 cm in height, which prevented view of the landscape (screened arena). The sandhoppers were introduced at the centre of the arena with a transparent tube in groups of ten. They were then released on the sand at the surface of the arena and captured at the periphery by the pit-fall traps. The two conditions, with and without landscape cues, were tested simultaneously. During the tests no artificial light was visible by the sandhoppers. Circular statistic analysis was used to examine the distributions obtained from the captures with the cross-pit-fall traps and the arenas. For each experiment mean vectors and the test statistic u (V-test for orientation seaward = 195°) were calculated from the capture frequencies of adults and juveniles and orientation tests in the arenas (Batschelet 1981). The uniformity of distribution was checked with the Rayleigh test . The influence of environmental parameters on the capture frequency and on the orientation of the sandhoppers was tested by multiple regression analysis, using the stepwise backward elimination method (Statgraphics 5.0, STSC Inc.). The test statistic u was used as orientation index. With the same method the number of burrowed individuals in the arenas was correlated with the environmental factors, considering also the total number of tested talitrids (weights).
Results
Surface activity of adults and juveniles was generally limited to nocturnal hours and a few hours after sunrise (Fig. 2). On one occasion individuals were active in the afternoon during and after rainfall (Fig. 2c). The activity of adults started 3, 4 or 1 h (Fig. 2a, b, c, respectively) after sunset, while the juveniles emerged from their burrows later in each case. There are slight rises in the adult catches around midnight and dips in the late-night period. In all cases both adults and juveniles presented maximum activities after dawn (Fig. 2). The orientation indexes (length of the mean vector, r), landward or seaward, of spontaneous movements, as well as the number of sandhoppers caught each hour and the probability of directed activity, are shown in Fig. 3. In the night of full moon, adults (Fig. 3a) showed movements significantly oriented only towards the sea, whereas juveniles (Fig. 3b) revealed a landward tendency at 01:00 hr ( p < 0.05). During the first quarter of the moon and at new moon, a clear landward migration occurred at night and a zonal recovery seaward around dawn and after sunrise (Fig. 3c–f ). Associated with rainfall, which took place on 29 June 1995 between 15:00 and 16:00 hrs, a migration of the sandhoppers towards land was recorded. Immediately after this peFig. 1 Talitrus saltator. Schematic view of trap positions in the riod, when the sun reappeared, a seaward migration was eulittoral. Distances between traps are illustrated. Tetradirectional pit- observed (Fig. 3e, f ). Also, the mean zonation of the fall traps were set at each position. Traps facing the shoreline sandhoppers, calculated according to the number of inintercepted sandhoppers moving from the water’s edge landwards (15° dividuals captured at different distances from the beach, in respect to north); those facing the supralittoral zone, individuals moving from the base of the dune seawards (195°); and the two other was significantly more landward at 16:00 hrs compared to 17:00 and 18:00 hrs (mean zonation at 16:00 hrs: traps, individuals moving along the shoreline (105° and 285°)
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Fig. 2 Talitrus saltator. Capture frequencies (n) of adults (d) and juveniles (s) for each hour. Shaded areas indicate period of darkness. Moonrise and moonset, together with period of rain, are also shown
13.58 ± 0.54 m from the shoreline; at 17:00 hrs: 10.95 ± 0.72 m; at 18:00 hrs: 7.92 ± 1.45 m). The aim of the arena experiments was to analyse which orientation mechanisms (landscape and/or sky cues) were used by the spontaneously active sandhoppers. The circular distributions in the arena tests are reported as examples only for several hours at the three different moon phases (Figs. 4–6). At 23:00 hrs seaward orientation is apparent in the full moon night (Fig. 4), while landward orientation is shown at 23:00 to 24:00 hrs with no moon visible, when a view of the landscape was permitted. In the screened arena the distributions are random (Figs. 5, 6). The scatter around 3:00 hrs is shown by the circular distributions both with screened and visible landscape (Figs. 4–6). Around dawn (5:00 hrs) all the distributions show a seaward tendency whether the landscape was visible or not (Figs. 4–6). In Fig. 7 the orientation indexes obtained in the arena experiments are reported for each hour. At full moon, seaward orientation was apparent throughout the night, both in the unscreened and screened arenas (Fig. 7a, b), with distributions random only at 03:00 hrs.
On the night of the lunar quarter, orientation experiments were not possible when the moon was visible because during this period only a few talitrids were caught. However, after moonset on this night, and in the new moon night, individuals were significantly landward oriented when tested with visible landscape (Fig. 7c, e). In the screened arena, when only the sky was visible, the distributions were random (Fig. 7d, f ). Around dawn and at sunrise the sandhoppers were significantly seaward oriented both with visible and screened landscape (Fig. 7c–f ). The change from landward to seaward migration was preceded by a period of random movement (Fig. 7c, e). During the orientation tests some individuals promptly burrowed in the sand on the surface of the arenas. The percentages of individuals showing this behaviour are reported for each test (Fig. 8). In the full moon night, the maxima of burrowing tendencies were at 3:00 (unscreened arena) and 4:00 hrs (screened arena) which corresponds to the time of low spontaneous activity registered with the traps, and low orientation index both in the beach and in the arenas (compare Fig. 8a, b with Figs. 2a and 7a, b). In the quarter of moon night, the maximum of burrowing tendency was at 22:00 to 23:00 hrs, respectively, in the unscreened and screened arena, which also corresponds to the period of low spontaneous activity (compare Fig. 8c, d with Fig. 2b). In the new moon night, burrowing tendency was shown before midnight and at 7:00 hrs, also in correspondence with low surface activity (compare Fig. 8e, f with Fig. 2c). Tables 1 to 3 show the results of the multiple regression analysis of the sandhopper’s surface activity (capture frequency), orientation (u) and burrowing tendency (burrowed, n), along with environmental parameters, in the three test nights. In the full moon night, the activity of both adults and juveniles was negatively correlated with sand temperature, that of the juveniles also with sand moisture (Table 1). Adult orientation during the spontaneous movements was influenced by a complex of factors, both climatic, air humidity and atmospheric pressure, and visual, the moon height above the horizon. The two latter factors were correlated negatively. On the 26/27 April 1994 atmospheric pressure was gradually rising, following a period of rain, and air temperatures and humidity ranged from 22 °C and 36% during the day to 8 °C and 74% around dawn. During the full moon night, arena tests were not analysed because the data were insufficient for multiple regression analysis. In the lunar quarter experiment, the activity of adults was negatively correlated with air temperature and humidity, and positively with atmospheric pressure (Table 2). By contrast the juvenile activity was positively correlated with air temperature and relative humidity, and negatively with the deep sand temperature. The adult orientation during spontaneous migration had negative correlation with atmospheric pressure and deep sand temperature. According to multiple regression analysis, no environmental parameter significantly af-
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Fig. 3 Talitrus saltator. Orientation indexes (r = length of the mean vector obtained from the tetradirectional pit-fall traps) are shown for each hour. Numbers accompanying each data point indicate total capture frequency for each hour; significant levels of probability of directedness according to Rayleigh test are given (**p > 0.01; *p < 0.05)
fected juvenile orientation. In the screened arena tests the air temperature was negatively correlated with orientation. The burrowing tendency in the arenas was positively correlated with atmospheric pressure. Air temperatures and humidities ranged from 23 °C and 67% at 16:00 hrs to 10 °C and 87% at 06:00 hrs. In the new moon night, adult activity was negatively correlated with the surface sand temperature, that of the juveniles with wind speed (Table 3). The adult orienta-
tion during spontaneous movements was positively correlated with air temperature and humidity, and negatively with the deep sand temperature. Positive correlations were found between juvenile orientation and air relative humidity, surface sand temperature and wind. The orientation in the arena tests was positively correlated with the air temperature and humidity and sand moisture, while the burrowing tendency was correlated positively with the sand surface temperature. On 29/30
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Fig. 4 Talitrus saltator. Full moon night (26/27 April 1994). Distributions obtained in unscreened (which permitted the view of both sky and landscape) and screened (which permitted the view of sky only) arenas at 23:00, 03:00 and 05:00 hrs are shown as examples. For each distribution are reported: the individual choices (dots); the mean vector, r, with its direction and length; p for the Rayleigh test. Undulated lines represent the sea
June 1995 the atmospheric pressure values went down during rainfall in the afternoon and up again during the night, and air temperature and humidity ranged from 26 °C and 68% at 18:00 hrs to 16 °C and 93% at 04:00 hrs.
Discussion The results confirm that the feeding migration of talitrids on a Mediterranean beach occurs at night and is generally oriented landward after sunset and seaward around dawn (Scapini et al. 1992). However, such migration does not occur each night, depending on environmental factors (Geppetti and Tongiorgi 1967). According to our data, during the full moon night movements were seaward oriented. This could be ex-
Fig. 5 Talitrus saltator. Quarter of moon night (11/12 October 1994). Distributions obtained in unscreened and screened arenas at 24:00, 03:00 and 05:00 hrs are shown as examples. For further explanations see Fig. 4
plained considering that in the days before the experiment it had rained, and the relative humidity was high even during the daylight hours. This had permitted an even distribution of the sandhoppers in the eu- and supralittoral zone of the beach. The seaward movements (see orientation indexes with both pit-fall traps and arenas) registered during the full moon experiments can be interpreted as a recovery of the zone close to the shoreline limits, where the sandhoppers normally live. The adults migrated from the upper beach zone during the whole night, whereas the juveniles moved predominantly after dawn. This could indicate that the adults had gone farther upshore than the juveniles. For the latter a negative correlation was found with surface sand moistures, showing the importance of this parameter for individuals smaller in size during their period of activity. The landward and seaward movements which were observed during the day (29 June 1995) associated with rainfall can be interpreted as a zonal recovery, to avoid overly wet substrate during rainfall (landwards movement) and desiccated substrate following insolation
0.0000 NS NS – – NS NS NS NS
– NS NS NS NS
NS
Adult orientation (u)
Juvenile orientation (u)
1.530 p = 0.0201
)282.489 p = 0.0293 )25.034 p = 0.0011 NS NS NS Juvenile surface activity (n)
NS
)0.923 13773 p = 0.0045 p = 0.0090 – )18.166 p = 0.0089
0.8129
0.6480 641.284 p = 0.0051 NS NS
0.3512 77.330 p = 0.0020 NS – – NS NS NS Adult surface activity (n)
NS
)6.100 p = 0.0248
NS
R2 Constant Moon height (°) Wind direction (°) Wind speed (m s)1) Atmospheric pressure (mmHg) Surface sand moisture (%) Deep sand temperature (°C) Surface sand temperature (°C) Air relative humidity (%)
(seawards movement). The mean zonations of the sandhoppers confirm that rain affects the individuals for a limited period of time, because they are again found in their preferred zone before the onset of spontaneous nocturnal activity. During the lunar quarter and new moon nights, sandhoppers with a zonation already close to the water’s edge migrated landward at night to forage and then seaward to burrow back at the water’s edge. This pattern is in accordance with the previous data on Mediterranean beaches and differs from Atlantic patterns in which sandhoppers migrate seaward to forage (Geppetti and Tongiorgi 1967; Williams 1983; Scapini et al. 1992). The data show the importance of internal factors for determining the direction of orientation; the change from the landward to seaward movement apparently occurs at a certain time of the night, anticipating sunrise, when air temperature is still low and humidity high. An internal orientation mechanism was
Air temperature (°C)
Fig. 6 Talitrus saltator. New moon night (29/30 June 1995). Distributions obtained in unscreened and screened arenas at 23:00, 03:00 and 05:00 hrs are shown as examples. For further explanations see Fig. 4
Table 1 Talitrus saltator. Full moon night (26/27 April 1994). Multiple regression analysis of adult and juvenile surface activity (n) and orientation (u), with environmental parameters. Coefficients of determination (R2) and partial regression coefficients with probability levels ( p) are shown (NS not significant; – not measured)
68
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first demonstrated by Edwards and Naylor (1987). Here, it is confirmed for natural conditions. Particularly interesting is the evidence of scatter at the time of the change of direction in the orientation of sandhoppers. A similar scatter at a certain time of the night was observed for scototaxis under constant laboratory conditions by Mezzetti et al. (1994), and a change in internal drive may be a cause for the change of direction and the scatter in correspondence to it.
From the multiple regression analysis it follows that the most important environmental factor influencing spontaneous activity and migration is sand temperature. This could explain the variation in timing of emergence observed in nature. Environmental limiting factors, such as low relative air humidity, rainfall or temperature extremes, may modulate the internal drive to emerge. A burrowing tendency was recorded in the arena tests with limiting environmental factors. Also, the light of the
Fig. 7 Talitrus saltator. Orientation indexes (r = length of the mean vector) obtained from the distributions in the two arenas, screened and unscreened. Numbers accompanying each data point indicate size of the distribution. For further explanations see Fig. 3
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Fig. 8 Talitrus saltator. Percentages of sandhoppers burrowing in the sand in unscreened and screened arenas are reported for each hour of experiment. Numbers accompanying each data point indicate the number of individuals tested for each hour (including both the individuals that reached the rim of the arena and those burrowing at its surface)
moon may influence sandhopper orientation at least in full moon nights. The present study showed evidence of a negative correlation between orientation and moon height. The importance of environmental factors in modulating behaviour is supported also by the differences observed between adults and juveniles, which are affected differently by such factors due to size variance. Particularly, wind affects the behaviour of juveniles only. Atmospheric pressure may also influence the spontane-
ous activity and orientation of sandhoppers when its changes announce a weather change. This may cause a variation along the sea–land gradients and consequently in amphipod zonation. A similar effect was shown in a population of Tylos europaeus Arcangeli, 1938, living in the same locality and beach zone (Fallaci et al. 1996). The main purpose of the present study was to determine which orienting factor guides the spontaneous movements in nature. The results clearly show that in
)7.102 p = 0.0259
NS
NS
)24.376 p = 0.0045
9.563 p = 0.0148
NS
NS
)4.238 p = 0.0004
NS
NS
NS
Adult surface activity (n)
Juvenile surface activity (n)
Adult orientation (u)
Juvenile orientation (u)
Screened arena orientation (u)
Unscreened arena orientation (u)
Screened arena burrowed (n)
Unscreened arena burrowed (n)
NS
NS
NS
NS
NS
NS
NS
NS
NS
)6.246 p = 0.0424
–
–
–
–
NS
NS
NS
NS
NS
NS
)28.036 p = 0.0080
NS
NS
6.211 p = 0.0011
5.863 p = 0.0020
NS
NS
NS
)4.418 p = 0.0154
NS
1.303 p = 0.0100
–
–
–
–
NS
NS
NS
NS
Surface sand Atmospheric Wind speed moisture pressure (%) (mmHg) (m s)1)
NS
Surface sand Deep sand temperature temperature (°C) (°C)
–
–
–
–
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
0.0000 0.7893 0.8279
)4475.054 p = 0.0020 )4741.098 p = 0.0011
0.8777
0.0000
0.4906
0.4490
0.5980
R2
NS
49.711 p = 0.0004
NS
3487.459 p = 0.0138
NS
NS
(°)
(°) NS
Moon height Constant
Wind direction
NS
NS
21.328 p = 0.0126
NS
6.923 p = 0.0159
11.544 p = 0.0038
NS
NS
Adult surface activity(n)
Juvenile surface activity (n)
Adult orientation (u)
Juvenile orientation (u)
Screened arena orientation (u)
Unscreened arena orientation (u)
Screened arena burrowed (n)
Unscreened arena burrowed (n)
Air temperature (°C)
NS
NS
4.022 p = 0.0064
2.440 p = 0.0230
1.207 p = 0.0346
6.838 p = 0.0272
NS
NS
Air relative humidity (%)
1.017 p = 0.0366
NS
NS
NS
1.843 p = 0.0318
NS
NS
–
–
–
–
NS
NS
21.040 p = 0.0416
NS
NS
NS
)5.114 p = 0.0156 NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
–
–
–
–
NS
NS
–
–
–
–
0.032 p = 0.0200
NS
NS
)0.021 p = 0.0433
–
–
–
–
–
–
–
–
0.3997 0.6138
)340.157 p = 0.0118 )576.094 p = 0.0049
NS
0.2024
0.0000
0.3743
)132.730 p = 0.0368
NS
0.4941
0.1732
0.3601
R2
)858.97 p = 0.0369
84.02 p = 0.0068
751.31 p = 0.0003
(°)
(°) NS
Moon height Constant
Wind direction
NS
NS
)21.70 p = 0.0039 NS
Surface sand Atmospheric Wind speed moisture pressure (%) (mmHg) (m s)1)
Surface sand Deep sand temperature temperature (°C) (°C)
Table 3 Talitrus saltator. New moon night (29/30 June 1995). Multiple regression analysis of adult and juvenile surface activity, orientation in the field, orientation and burrowing tendencies in the arena tests, with environmental parameters. For further explanations see Table 1
NS
NS
NS
NS
4.293 p = 0.0047
Air relative humidity (%)
Air temperature (°C)
Table 2 Talitrus saltator. Quarter of moon night (11/12 October 1994). Multiple regression analysis of adult and juvenile surface activity, orientation in the field, orientation and burrowing tendencies in the arena tests, with environmental parameters. For further explanations see Table 1
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new moon nights a view of the landscape is necessary to guide the landward feeding migration, as in the screened arena no significant landward orientation appeared. In such conditions we can exclude both star and magnetic orientation. Mezzetti et al. (1994) have shown that the sensitivity of sandhoppers to blue light increases at night. This could increase the contrast of the landscape silhoutte on the horizon. However, when the moon was visible, a seaward orientation occurred even when view of the landscape was prevented, thus showing the importance of the moon as orienting cue. Furthermore, the light of the sky at dawn was sufficient to guide the seaward recovery. When the sun was visible, landscape cues were not necessary for seaward orientation. On the whole, this study, which was completely conducted in the field on spontaneously active individuals, points out the behavioural variability of sandhoppers in response to environmental factors. The internally driven changes in activity and orientation are modulated by environmental features in order to avoid stress and adjust zonation. Similar studies on the spontaneous activity of sandhoppers, conducted on the same beach in different years and seasons, and on different beaches, support this conclusion (Geppetti and Tongiorgi 1967; Karlbrink 1969; Williams 1980; Scapini et al. 1992 and unpublished). In the present study the spontaneous orientation pattern in the field was observed and experimentally investigated in relation to environmental factors, which both bring about and guide orientation. Evidence has been presented that sandhoppers are guided by the cues available in nature in an integrated way. Even if one orienting cue may be sufficient to guide migration, as is the case for landscape view, other cues, for example astronomic ones, are used by the sandhoppers if available. Better knowledge of this relationship will help to understand the conditions under which learning of orientation occurs. Acknowledgements We wish to thank the Italian W.W.F. (World Wildlife Fund) for its hospitality at the Oasi di Burano (Capalbio, Grosseto). This research was financed by M.U.R.S.T. (Ministero dell’Universita` e della Ricerca Scientifica; 60% and 40% funds), and by the Centro S.F.E.T. (Studi di Faunistica ed Ecologia Tropicali) of C.N.R. (Consiglio Nazionale delle Ricerche).
References Batschelet E (1981) Circular statistics in biology. Academic Press, London Bercken J van den, Broekhuizen S, Ringelberg J, Velthuis HHW (1967) Non visual orientation in Talitrus saltator. Experientia 23: 44–45
Craig P (1973) Orientation of the sand-beach amphipod, Orchestoidea corniculata. Anim Behav 21: 699–706 Edwards J, Naylor E (1987) Endogenous circadian changes in orientational behaviour of Talitrus saltator. J mar biol Ass UK 67: 17–26 Enright J (1972) When the beachhopper looks at the moon: the moon compass hypothesis. Animal orientation and navigation. National Aeronautics and Space Administration, Washington D.C., USA, pp 523–555 Ercolini A, Pardi L, Scapini F(1983) An optical directional factor in the sky might improve the direction finding of sandhoppers on the seashore. Monitore zool ital (NS) 17: 313–327 Ercolini A, Scapini F (1974) Sun compass and shore slope in the orientation of littoral amphipods (Talitrus saltator Montagu). Monitore zool ital (NS) 8: 85–115 Fallaci M, Colombini I, Taiti S, Chelazzi G (1996) Environmental factors influencing the surface activity and zonation of Tylos europaeus (Crustacea: Oniscidea) on a Tyrrhenian sandy beach. Mar Biol 125: 751–763 Geppetti L, Tongiorgi P (1967) Nocturnal migration of Talitrus saltator (Montagu) (Crustacea: Amphipoda). Monitore zool ital (NS) 1: 37–40 Hartwick RF (1976) Beach orientation in talitrid amphipods: capacities and strategies. Behavl Ecol Sociobiol 1: 447–458 Karlbrink F (1969) Distribution and dispersal of Talitridae (Amphipoda) in southern Sweden. Oikos 20: 327–334 Mezzetti M, Naylor E, Scapini F (1994) Rhythmic responsiveness to visual stimuli in different populations of talitrid amphipods from Atlantic and Mediterranean coasts: an ecological interpretation. J exp mar Biol Ecol 181: 279–291 Papi F (1960) Orientation by night: the moon. Cold Spring Harb Symp quant Biol 25: 475–480 Pardi L, Papi F (1953a) Ricerche sull’orientamento di Talitrus saltator (Montagu) (Crustacea: Amphipoda). I. L’orientamento durante il giorno di una popolazione del litorale tirrenico. Z vergl Physiol 35: 459–489 Papi F, Pardi L (1953b) Ricerche sull’orientamento di Talitrus saltator (Montagu) (Crustacea: Amphipoda). II. Sui fattori che regolano la variazione dell’angolo di orientamento nel corso del giorno. L’orientamento di notte. L’orientamento diurno di altre popolazioni. Z vergl Physiol 35: 490–518 Scapini F, Chelazzi L, Colombini I, Fallaci M (1992) Surface activity, zonation and migrations of Talitrus saltator on a Mediterranean beach. Mar Biol 112: 573–581 Scapini F, Pardi L (1979) Nuovi dati sulla tendenza direzionale innata nell’orientamento solare degli anfipodi litorali. Atti Accad naz Lincei Rc (Ser VIII) 66: 592–597 Ugolini A, Scapini F, Pardi L (1986) Interaction between solar orientation and landscape visibility in Talitrus saltator (Crustacea: Amphipoda). Mar Biol 90: 449–460 Verheijen FJ (1978) Orientation based on directivity, a directional parameter of the animal’s radiant environment. In: SchmidtKoenig K, Keeton WT (eds) Animal migration, navigation and homing. Springer-Verlag, Berlin, pp 447–457 Williams JA (1980) Environmental influence on the locomotor activity rhythm of Talitrus saltator (Crustacea: Amphipoda). Mar Biol 57: 7–16 Williams JA (1983) The endogenous locomotor activity rhythm of four supralittoral peracarid crustaceans. J mar biol Ass UK 63: 481–492 Williamson DJ (1951) Studies in the biology of Talitridae (Crustacea, Amphipoda): visual orientation in Talitrus saltator. J mar biol Ass UK 30: 91–99
