title: Resource tracking within and across continents in long-distance bird migrants.
abstract: Migratory birds track seasonal resources across and between continents. We propose a general strategy of tracking the broad seasonal abundance of resources throughout the annual cycle in the longest-distance migrating land birds as an alternative to tracking a certain climatic niche or shorter-term resource surplus occurring, for example, during spring foliation. Whether and how this is possible for complex annual spatiotemporal schedules is not known. New tracking technology enables unprecedented spatial and temporal mapping of long-distance movement of birds. We show that three Palearctic-African species track vegetation greenness throughout their annual cycle, adjusting the timing and direction of migratory movements with seasonal changes in resource availability over Europe and Africa. Common cuckoos maximize the vegetation greenness, whereas red-backed shrikes and thrush nightingales track seasonal surplus in greenness. Our results demonstrate that the longest-distance migrants move between consecutive staging areas even within the wintering region in Africa to match seasonal variation in regional climate. End-of-century climate projections indicate that optimizing greenness would be possible but that vegetation surplus might be more difficult to track in the future.
authors.affiliation: Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark.
authors.forename: Kasper
authors.identifier: 0000-0002-0320-0601
authors.initials: K
authors.lastname: Thorup
authors.affiliation: Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark.
authors.forename: Anders P
authors.identifier: 0000-0001-8776-9629
authors.initials: AP
authors.lastname: Tøttrup
authors.affiliation: Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark.
authors.forename: Mikkel
authors.identifier: 0000-0001-9363-6304
authors.initials: M
authors.lastname: Willemoes
authors.affiliation: Department of Biology, Lund University, Ecology Building, SE-22362 Lund, Sweden.; Dutch Montagu's Harrier Foundation, P.O. Box 46, 9679ZG Scheemda, Netherlands.; Conservation Ecology Group, Groningen Institute for Evolutionary Life Sciences, University of Groningen, P.O. Box 11103, 9700CC Groningen, Netherlands.
authors.forename: Raymond H G
authors.initials: RH
authors.lastname: Klaassen
authors.affiliation: Department of Biology, Lund University, Ecology Building, SE-22362 Lund, Sweden.
authors.forename: Roine
authors.initials: R
authors.lastname: Strandberg
authors.affiliation: Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark.
authors.forename: Marta Lomas
authors.identifier: 0000-0002-9397-8803
authors.initials: ML
authors.lastname: Vega
authors.affiliation: Centro de Geofisica de Évora, Universidade de Évora, 7000 Évora, Portugal.; Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.
authors.forename: Hari P
authors.identifier: 0000-0003-0628-4481
authors.initials: HP
authors.lastname: Dasari
authors.affiliation: Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark.; Museo Nacional de Ciencias Naturales, CSIC, Calle José Gutiérrez Abascal, 2, 28006, Madrid, Spain.; CIBIO-InBIO, Universidade de Évora, Largo dos Colegiais, 7000 Évora, Portugal.
authors.forename: Miguel B
authors.identifier: 0000-0002-5107-7265
authors.initials: MB
authors.lastname: Araújo
authors.affiliation: Department of Migration and Immuno-Ecology, Max Planck Institute for Ornithology, Radolfzell, Germany.; Department of Biology, University of Konstanz, Konstanz, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Wikelski
authors.affiliation: Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark.; Imperial College London, Silwood Park Campus, Ascot, Berkshire SL5 7PY, U.K.
authors.forename: Carsten
authors.identifier: 0000-0003-4585-0300
authors.initials: C
authors.lastname: Rahbek
mesh_terms: D000349:Africa; D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D001717:Birds / Q000502:physiology*; D057231:Climate Change; D005060:Europe; D012621:Seasons
keywords: Migration; NDVI; birds; climate change; seasonal vegetation