title: A migratory northern ungulate in the pursuit of spring: jumping or surfing the green wave?
abstract: The forage-maturation hypothesis (FMH) states that herbivores migrate along a phenological gradient of plant development in order to maximize energy intake. Despite strong support for the FMH, the actual relationship between plant phenology and ungulate movement has remained enigmatic. We linked plant phenology (MODIS-normalized difference vegetation index [NDVI] data) and space use of 167 migratory and 78 resident red deer (Cervus elaphus), using a space-time-time matrix of "springness," defined as the instantaneous rate of green-up. Consistent with the FMH, migrants experienced substantially greater access to early plant phenology than did residents. Deer were also more likely to migrate in areas where migration led to greater gains in springness. Rather than "surfing the green wave" during migration, migratory red deer moved rapidly from the winter to the summer range, thereby "jumping the green wave." However, migrants and, to a lesser degree, residents did track phenological green-up through parts of the growing season by making smaller-scale adjustments in habitat use. Despite pronounced differences in their life histories, we found only marginal differences between male and female red deer in this study. Those differences that we did detect pointed toward additional constraints on female space-use tactics, such as those posed by calving and caring for dependent offspring. We conclude that whereas in some systems migration itself is a way to surf the green wave, in others it may simply be a means to reconnect with phenological spring at the summer range. In the light of ubiquitous anthropogenic environmental change, understanding the relationship between the green wave and ungulate space use has important consequences for the management and conservation of migratory ungulates and the phenomenon of migration itself.
authors.affiliation: Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Aas, Norway. richard.bischof@umb.no
authors.forename: Richard
authors.initials: R
authors.lastname: Bischof
authors.forename: Leif Egil
authors.initials: LE
authors.lastname: Loe
authors.forename: Erling L
authors.initials: EL
authors.lastname: Meisingset
authors.forename: Barbara
authors.initials: B
authors.lastname: Zimmermann
authors.forename: Bram
authors.initials: B
authors.lastname: Van Moorter
authors.forename: Atle
authors.initials: A
authors.lastname: Mysterud
mesh_terms: D025041:Animal Migration; D000818:Animals; D057231:Climate Change; D003670:Deer / Q000502:physiology*; D063245:Plant Development; D012621:Seasons