Aim
In general, within temperate latitudes, races of endotherms tend to show larger body size at higher latitudes, while smaller bodied ones tend to be found at lower latitudes, a pattern known as Bergmann's rule (or James's rule for intra‐specific patterns). The adaptive basis of this geographical variation in body size is explained mostly by the heat conservation hypothesis. Application of Bergmann's rule has been confirmed mostly among terrestrial taxa and studies of marine taxa are rare. Our aim was to examine whether the intra‐specific variation in body size of a pelagic seabird species (streaked shearwater Calonectris leucomelas) follows Bergmann's/James's rule.
Location
Eight different breeding colonies of the streaked shearwater, ranging from 24–39° N in latitude (approximately the full latitudinal range of the species) and 123–142° E in longitude.
Methods
We measured morphological traits of 454 adult streaked shearwaters in total. Principal components analysis was used to create a composite body size index for each sex from each colony using the measured traits, and the value of first principal component was compared. The relationships between body size index and latitude, longitude and the averaged mean air temperature were examined using generalized linear models.
Results
Body size was positively correlated with latitude and longitude, and negatively correlated with the mean air temperature. Latitude and longitude were highly correlated with air temperature. Nonetheless, between colonies, populations that are considered to forage over large areas appeared to exhibit smaller body size than those of lower latitude populations.
Main conclusion
The overall trend of the geographical variations in body size of streaked shearwaters followed Bergmann's/James's rule, suggesting that this rule may be applicable to seabirds. However, in addition to thermoregulatory adaptation, intra‐specific differences in foraging characteristic in relation to local marine environment might also affect the body size in highly mobile seabirds.
1998~2000年に実施された日露共同標識調査の結果から,優占種,日周変化,再捕獲記録,主 な種の渡り時期について解析した. ₃ 年間で合計46種5,278羽が標識放鳥され,21種361羽が再捕 montifringilla, migrated late. The data also showed that juveniles of Red-breasted Flycatcher, Rustic Bunting and Reed Bunting, which don't molt in the breeding area, migrated earlier than the adults, which molt completely in the breeding area. The juveniles of Common Rosefinch and Arctic Warbler, in contrast were found to migrate later than the adults, which molt in their wintering area. The captures and measurements obtained showed that the timing of body fat increase corresponded with the peak of migration in adults, but was about 10 days later in juveniles. This may account probably for juveniles taking a longer time to complete the migration than adults.
Abstract. Streaked Shearwaters Calonectris leucomelas breed along the northwest Pacific coast, and winter in Australia and Southeast Asia. Previous studies at nesting sites on islands off the Japanese coast have indicated that males and females give different mating calls. This research, implemented at a breeding colony on Kanmuri Island, Kyoto Prefecture, showed that there were differences in the external measurements of Streaked Shearwaters giving low-pitch and high-pitch vocalizations. A discriminant function: Dϭ216.400Ϫ2.318ϫTHLϪ4.074ϫBWϩ2.007ϫNALϪ1.929ϫBD, where THL is total head length, BW is width of bill at anterior edge of nostril, NAL is nalopsi and BD is depth of bill at anterior edge of nostril, was derived from external measurements of adult shearwaters giving low-pitch (41 birds) and high-pitch (41 birds) calls. D was positive for the birds with low-pitch calls and negative for the birds with high-pitch calls. This function proved reliable for 97.6% of the low-pitch individuals and for 95.1% of the high-pitch individuals, thus vocalization may be a useful means of sex identification in the field.
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