title: Migratory herbivorous waterfowl track satellite-derived green wave index.
abstract: 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.
authors.affiliation: Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, The Netherlands.
authors.forename: Mitra
authors.initials: M
authors.lastname: Shariatinajafabadi
authors.affiliation: Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, The Netherlands.
authors.forename: Tiejun
authors.initials: T
authors.lastname: Wang
authors.affiliation: Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, The Netherlands.
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Skidmore
authors.affiliation: Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, The Netherlands.
authors.forename: Albertus G
authors.initials: AG
authors.lastname: Toxopeus
authors.affiliation: 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.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kölzsch
authors.affiliation: Department of Animal Ecology and Project group Movement Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.
authors.forename: Bart A
authors.initials: BA
authors.lastname: Nolet
authors.affiliation: Institute of Avian Research, Wilhelmshaven, Germany.
authors.forename: Klaus-Michael
authors.initials: KM
authors.lastname: Exo
authors.affiliation: Wildfowl & Wetlands Trust, Slimbridge, Gloucestershire, United Kingdom.
authors.forename: Larry
authors.initials: L
authors.lastname: Griffin
authors.affiliation: Sovon Dutch Centre for Field Ornithology, Nijmegen, The Netherlands.
authors.forename: Julia
authors.initials: J
authors.lastname: Stahl
authors.affiliation: Environmental Consultancy Services, Carrigskeewaun, Carrowniskey, Westport, Co. Mayo, Ireland.
authors.forename: David
authors.initials: D
authors.lastname: Cabot
mesh_terms: D000531:Altitude; D000704:Analysis of Variance; D025041:Animal Migration; D000818:Animals; D018533:Biomass; D005523:Food Supply; D005777:Geese / Q000502:physiology*; D006116:Greenland; D060434:Herbivory / Q000502:physiology*; D016018:Least-Squares Analysis; D008954:Models, Biological; D010944:Plants; D012426:Russia; D012621:Seasons; D018531:Spacecraft; D013538:Svalbard