Smithsonian Migratory Bird Center, National Zoological Park, 3001 Connecticut Avenue, Washington, DC 20008, USA.
Ecology. 2010 Oct;91(10):2874-82. doi: 10.1890/09-2212.1.
Identifying the determinants of habitat quality for a species is essential for understanding how populations are limited and regulated. Spatiotemporal variation in moisture and its influence on food availability may drive patterns of habitat occupancy and demographic outcomes. Nonbreeding migratory birds in the neotropics occupy a range of habitat types that vary with respect to moisture. Using carbon isotopes and a satellite-derived measure of habitat moisture, we identified a moisture gradient across home ranges of radio-tracked Northern Waterthrush (Seiurus noveboracensis). We used this gradient to classify habitat types and to examine whether habitat moisture correlates with overwinter mass change and spring departure schedules of Northern Waterthrush over the late-winter dry season in the tropics. The two independent indicators of moisture revealed similar gradients that were directly proportional to body mass change as the dry season progressed. Birds occupying drier habitats declined in body mass over the study period, while those occupying wetter habitats increased in body mass. Regardless of habitat, birds lost an average of 7.6% of their mass at night, and mass recovery during the day trended lower in dry compared with wet habitats. This suggests that daily incremental shortfalls in mass recovery can lead to considerable season-long declines in body mass. These patterns resulted in consequences for the premigratory period, with birds occupying drier habitats having a delayed rate of fat deposition compared with those in wet habitats. Taken together with the finding that males, which are significantly larger than females, are also in better condition than females regardless of habitat suggests that high-quality habitats may be limited and that there may be competition for them. The habitat-linked variation in performance we observed suggests that habitat limitation could impact individual and population-level processes both during and in subsequent periods of the annual cycle. The linkage between moisture and habitat quality for a migratory bird indicates that the availability of high-quality habitats is dynamic due to variation in precipitation among seasons and years. Understanding this link is critical for ascertaining the impact of future climate change, particularly in the Caribbean basin, where a much drier future is predicted.
确定物种生境质量的决定因素对于理解种群如何受到限制和调节至关重要。水分的时空变化及其对食物供应的影响可能会影响栖息地的占有模式和人口的结果。新热带地区的非繁殖候鸟占据了一系列与水分有关的不同栖息地类型。我们使用碳同位素和卫星衍生的栖息地水分测量值，确定了在无线电追踪的北方水鸫（Seiurus noveboracensis）的家域范围内的水分梯度。我们利用这个梯度来对栖息地类型进行分类，并研究在热带地区的旱季末期，北方水鸫的栖息地水分是否与越冬体重变化和春季出发时间有关。这两个独立的水分指标揭示了相似的梯度，这些梯度与随着旱季的进行体重变化成正比。在研究期间，栖息在较干燥栖息地的鸟类体重下降，而栖息在较湿润栖息地的鸟类体重增加。无论栖息地如何，鸟类在夜间平均失去 7.6%的体重，而在较干燥的栖息地，白天体重恢复的趋势较低。这表明，每日增量体重恢复不足可能导致整个季节体重的大幅下降。这些模式对迁徙前的时期产生了影响，与栖息在湿润栖息地的鸟类相比，栖息在干燥栖息地的鸟类脂肪沉积速度较慢。再加上发现雄性无论栖息地如何，都比雌性体型大，并且状态也比雌性好，这表明高质量的栖息地可能是有限的，而且可能存在对它们的竞争。我们观察到的与栖息地相关的性能变化表明，栖息地限制可能会影响个体和种群在年度周期的各个时期和随后的时期的过程。候鸟与栖息地之间的这种联系表明，由于季节和年份之间降水的变化，高质量栖息地的供应是动态的。了解这种联系对于确定未来气候变化的影响至关重要，特别是在预测未来会更加干燥的加勒比海盆地。
