Costa Rican spinner dolphins are found in large schools of >1,000 in coastal waters off the west coast of Central America. This social pattern of atoll-dwelling spinner dolphins is considerably different from the pattern described previously for spinner dolphins associated with a large island habitat in the main Hawaiian Archipelago (Norris et al., 1994). Most have long thin beaks with the exception of Clymene dolphins (Atlantic short-snouted spinners). The regional populations vary in size. In these same subspecies, a dark dorsal cape dims their tripartite color patterns. However, the decrease in lagged association rates projected over 550 days was very low, and the graphic display (and accuracy, measured with AIC) of this model differed only slightly from the next best-fit model, which was constant companions (broken line in Figure 4). Dwarf spinner dolphins are found in the Gulf of Thailand. This is consistent with other studies of vertebrate social structure reviewed by Whitehead and Dufault (1999). Simulations using half-weight and simple ratio indices (Whitehead, 1999a) indicate that if some pairs of animals preferentially associate with one another at different sampling periods more often than by chance, this significantly increases the SD of the observed association indices versus the randomly permuted data. These surveys were carried out at a sea state of Beaufort scale ≤3 and always covered the entire inner lagoon, unless deteriorating weather conditions truncated a survey. The nighttime pattern of associations remains unknown (Norris and Johnson, 1994; Würsig et al., 1994c). We are committed to preserving the ocean and its inhabitants. When possible, the age of calf and month of birth were estimated. Maximum association indices showed little variability, suggesting a high level of group stability (Table 1). They have small, pointed flippers and curved dorsal fins at the center of their bodies. Calves are defined as animals 2/3 or less the length of an adult, regularly accompanying a larger animal presumed to be the mother. The residence rate of individuals was measured by calculating lagged identification rates, which represent the probability that an individual identified at any particular time will be identified again in the study area t time units later (sensu Whitehead, 2001). Bigg MA, Olesiuk PF, Ellis GM, Ford JKB, Balcomb KC III. In this study, lagged and null association rates were standardized (divided by the number of recorded associates, Whitehead, 1999a) because it was logistically difficult to photograph all individuals in a group. 12520-01014. For immigrants, the model best describing the observed pattern of associations was “constant companions” (sensu Whitehead, 1995), which indicates stable associations over time, changed only by birth or death. Leszek Karczmarski, Bernd Würsig, Glenn Gailey, Keith W. Larson, Cynthia Vanderlip, Spinner dolphins in a remote Hawaiian atoll: social grouping and population structure, Behavioral Ecology, Volume 16, Issue 4, July/August 2005, Pages 675–685, https://doi.org/10.1093/beheco/ari028. In this process, geographic isolation of socially stable, bisexually bonded dolphin societies facilitates social discreteness and differential social structures, which in turn add another barrier—a social barrier—to the gene flow and affect population genetic structure. The animals were photographed with a motorized camera equipped with a variable length (zoom 100–300 mm) lens and 100 ISO color positive film. Lagged identification rates were calculated and models fitted for all adults and for each sex separately. The study described here investigates the pattern of group living and social dynamics of a population of spinner dolphins associated with remote Midway Atoll, northwestern Hawaii. Known predators are sharks, orca (killer whales), and possibly false killer whales, pygmy killer whales, and pilot whales. The characteristic spinning of this species is thought to be used for communication as it is often observed when a school is scattered. We applied photoidentification mark-recapture techniques to study the population structure of spinner dolphins associated with remote Midway Atoll, far-western Hawaii. This individual sighting history, representing a case of emigration and reimmigration, as suggested by the model best fitting the residents' lagged identification rates, is very likely an example of such occasional interactions between the neighboring populations. Permutation tests for preferential companionship were run on the 1999 data set when two dolphin groups were present. It is unlikely, however, that they take place often, as the individuals known to use the geographically closest atolls (Midway residents and the immigrants seen previously at Kure) showed little interaction and remained socially discrete for many months when exposed to each others' presence at one location. Several studies of terrestrial mammalian systems show considerable intraspecific variability, a result of individual attempts to maximize fitness under local ecological conditions (Bekoff et al., 1984; Boesch, 2002; Boinski, 1999; Wrangham, 1987). Although the “daytime home ranges” of residents and immigrants overlapped extensively at Midway and both groups often resided in areas only 2–3 km distant, they interacted little, often remaining separate for the entire time within the lagoon. Three major dolphin adaptations include swimming ability, echolocation and group hunting skill. Box 50167, Honolulu, HI 96850, USA, Oxford University Press is a department of the University of Oxford. An intriguing parallel becomes apparent: that social dynamics of complex mammalian societies, even evolutionarily as distant as delphinids and primates, vary in a remarkably similar way if exposed to comparable ecological and social selective pressures. For 2 days in mid-October 1998, ID-photographs were collected at Kure Atoll. Individuals of approximately 2 m length, with the height of the dorsal fin generally equal to their length, were classified as adults. and whether or not an individual was already photographed. The mean association index for the observed data was significantly lower than the randomly permuted data, and the SD of the mean association index of the observed data was significantly higher than the randomly permuted data (Table 2). 1994a). 1007-1629-01 and U.S. Movement pattern was monitored with a portable geographic positioning system and recorded in 10-min intervals, as were water clarity, temperature, depth, and the general features of the bottom topography. It literally uses its head as a net!
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