Shariatinajafabadi Mitra, Wang Tiejun, Skidmore Andrew K, Toxopeus Albertus G, Kölzsch Andrea, Nolet Bart A, Exo Klaus-Michael, Griffin Larry, Stahl Julia, Cabot David
Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, The Netherlands.
Max Planck Institute for Ornithology, Department of Migration and Immuno-Ecology, Vogelwarte Radolfzell, Radolfzell, Germany; Department of Animal Ecology and Project group Movement Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.
PLoS One. 2014 Sep 23;9(9):e108331. doi: 10.1371/journal.pone.0108331. eCollection 2014.
Many migrating herbivores rely on plant biomass to fuel their life cycles and have adapted to following changes in plant quality through time. The green wave hypothesis predicts that herbivorous waterfowl will follow the wave of food availability and quality during their spring migration. However, testing this hypothesis is hampered by the large geographical range these birds cover. The satellite-derived normalized difference vegetation index (NDVI) time series is an ideal proxy indicator for the development of plant biomass and quality across a broad spatial area. A derived index, the green wave index (GWI), has been successfully used to link altitudinal and latitudinal migration of mammals to spatio-temporal variations in food quality and quantity. To date, this index has not been used to test the green wave hypothesis for individual avian herbivores. Here, we use the satellite-derived GWI to examine the green wave hypothesis with respect to GPS-tracked individual barnacle geese from three flyway populations (Russian n = 12, Svalbard n = 8, and Greenland n = 7). Data were collected over three years (2008-2010). Our results showed that the Russian and Svalbard barnacle geese followed the middle stage of the green wave (GWI 40-60%), while the Greenland geese followed an earlier stage (GWI 20-40%). Despite these differences among geese populations, the phase of vegetation greenness encountered by the GPS-tracked geese was close to the 50% GWI (i.e. the assumed date of peak nitrogen concentration), thereby implying that barnacle geese track high quality food during their spring migration. To our knowledge, this is the first time that the migration of individual avian herbivores has been successfully studied with respect to vegetation phenology using the satellite-derived GWI. Our results offer further support for the green wave hypothesis applying to long-distance migrants on a larger scale.
许多迁徙的食草动物依靠植物生物量来维持其生命周期，并已适应随着时间推移跟踪植物质量的变化。绿波假说预测，食草水禽在春季迁徙期间会跟随食物可获得性和质量的浪潮。然而，由于这些鸟类覆盖的地理范围很大，对这一假说的验证受到了阻碍。卫星衍生的归一化植被指数（NDVI）时间序列是一个理想的代理指标，可用于反映广泛空间区域内植物生物量和质量的变化。一个衍生指数，即绿波指数（GWI），已成功用于将哺乳动物的海拔和纬度迁移与食物质量和数量的时空变化联系起来。迄今为止，该指数尚未用于检验单个食草鸟类的绿波假说。在这里，我们使用卫星衍生的GWI，针对来自三个飞行路线种群（俄罗斯n = 12、斯瓦尔巴群岛n = 8和格陵兰n = 7）的GPS跟踪的单个黑雁来检验绿波假说。数据收集历时三年（2008 - 2010年）。我们的结果表明，俄罗斯和斯瓦尔巴群岛的黑雁跟随绿波的中期阶段（GWI 40 - 60%），而格陵兰的黑雁跟随更早的阶段（GWI 20 - 40%）。尽管不同雁群之间存在这些差异，但GPS跟踪的雁所遇到的植被变绿阶段接近50%的GWI（即假定的氮浓度峰值日期），这意味着黑雁在春季迁徙期间跟踪高质量食物。据我们所知，这是首次使用卫星衍生的GWI成功研究单个食草鸟类的迁徙与植被物候的关系。我们的结果为绿波假说在更大规模上适用于长途迁徙者提供了进一步支持。
