Yellow-rumped Warblers Dendroica Coronata Research Articles

神奈川県鎌倉市で観察されたキヅタアメリカムシクイDendroica coronataの日本初記録

神奈川県鎌倉市で観察されたキヅタアメリカムシクイDendroica coronataの日本初記録

Migration-Induced Variation in Thermogenic Capacity in Migratory Passerines

Increases in maximal capacity for thermogenesis (or Peak Metabolic Rate, PMR) are typically associated with winter acclimatization in passerines showing marked seasonal changes in cold tolerance. Thermogenic capacity also increases in spring migrant Warbling Vireos Vireo gilvus, a Neotropical migrant, relative to summer acclimatized individuals, but a similar increase does not occur in fall migrants. We tested whether migratory disposition was associated with variation in thermogenic capacity in another Neotropical migrant passerine, the Yellow Warbler Dendroica petechia, and in two passerine species migrating to mild temperate regions in winter, Yellow-rumped Warbler Dendroica coronata and Ruby-crowned Kinglet Regulus calendula. PMR was elicited by cold exposure in an atmosphere of 79% helium:21% oxygen during spring and fall migration for all species, and also during summer for Yellow Warblers. Yellow and Yellow-rumped Warblers both exhibited significantly higher thermogenic capacity in spring than at other seasons (23.3% greater than pooled summer and fall values in Yellow Warblers, 19.8% greater than in fall Yellow-rumped Warblers). For kinglets, males showed significantly higher PMR in spring than in fall (10.9%), but PMR did not vary seasonally in females. Thus, these species conform to a pattern of elevated thermogenic capacity in spring relative to other seasons, at least in the sex establishing breeding territories, suggesting that this may be a common pattern in migratory passerines. Mild temperate migrants migrate earlier in spring and later in fall than Neotropical migrants and, as a consequence, experience less variation in temperature between spring and fall migrations. Nevertheless, PMR varied similarly on a seasonal basis among Neotropical and mild-temperate migrants, despite the greater seasonal variation in temperatures encountered by Neotropical migrants. Moreover, ANCOVA on log PMR with log mass as a covariate did not demonstrate systematically lower PMR in Neotropical migrants than in mild temperate migrants for the species in this study, despite the differences in temperatures encountered during migration. This suggests that seasonal changes in PMR during migration are not associated with temperature acclimatization, but instead vary with other features of migratory patterns.

A comparison of foliage use and tree height selection by birds in unlogged and logged mixed-coniferous forest

Tree height selection and use of the available foliage by birds were examined in two mixed-coniferous forests in the White Mountains, Arizona, USA, during 1973 and 1974. A comparison of avian habitat use between a natural forest and one which had recently undergone a moderately heavy overstory removal form of timber harvesting, revealed that in both areas tall and moderately tall trees were preferred. Comparisons were made for the composite avian community and, in particular, for the yellow-bellied sapsucker Sphyrapicus varius, mountain chickadee Parus gambeli, ruby-crowned kinglet Regulus calendula, yellow-rumped warbler Dendroica coronata, and dark-eyed (= grey-headed) junco Junco hyemalis caniceps. Taller trees provided substantially more foliage and substrate for nesting and foraging than did shorter ones. Foliage use by birds in the unharvested plot suggested that foliage was being used in approximately the proportion in which it was available. This was not true in the modified plot where quaking aspen Populus tremuloides—the only tree species not logged—comprised 53·1% of the total available foliage volume. The biggest discrepancy between bird use and foliage volume occurred between 9 and 21 m from the ground. Within this height interval aspen represented 63·8% of the total volume. The subsequently derived bird use curve reflected the reduced desirability of aspen for most avian species.