Herbivores often encounter forage that is largely indigestible, of low nutritional value and patchily distributed: the green world is far from being universally edible of universally nutritious.
Feeding strategies of avian herbivores are dictated by the occurrence of food pulses, i.e. peaks in plant production with forage of high nutritional quality that are transient in space and time. Migratory geese commute between coastal ecosystems of the temperate and arctic zone during their annual cycle. The timing of spring migratory movements is postulated to hinge upon seasonal changes in availability and profitability of plant resources along the flyway, formalised as the ‘Green Wave Hypothesis’. For experimental testing of this hypothesis, we use the Barnacle Goose as a flagship species. Traditionally breeding at arctic sites, the Barnacle Goose population recently showed a spectacular expansion of the breeding range towards the temperate regions (Baltic and
North Sea
coast line).
Thus, within the same flyway, long-distance migrating arctic birds apparently follow the nutritional peak of their forage plants as they migrate to high arctic sites where they encounter long daylight hours, but a short breeding season. In contrast, medium-distance migrants have colonized a former traditional stop-over site where they profit from an extended breeding season but have to cope with a seasonal decline in forage quality which substantially delays gosling growth. The Flyway now entails t
hree barnacle goose populations, one arctic-breeding, one breeding in the Baltic, and one sedentary population along the
North Sea
coastline. All three populations share the same wintering grounds, although on a subtler level habitat choice and range differ. However, populations differ in important life-history parameters, notably timing of reproduction and moult, clutch size, and growth rates of young.
Current research activities focus on the identification of energetic needs of migrating and breeding barnacle geese, on interactions between different herbivores along the flyway, on the influence of climate change on forage plants and the flexibility in the timing of the migration. The project relies on the close co-operation between research groups with expertise in animal energetics and foraging ecology in relation to avian migration (CEES Animal Ecology Group) and vegetation dynamics and coastal ecology (CEES Community and Conservation Ecology Group). A major advantage is the presence of a well-equipped field station on the island Schiermonnikoog. This offers an ideal venue for calibration of techniques to assess digestibility of natural forages and the energy budgets of unrestrained geese against the background of a well documented plant-herbivore system where all important players are the subject of intensive study. Only recently has it become feasible to follow the geese on their migration and implement experimental field studies at sites crucial to the persistence of these Arctic populations. Expeditionary work is undertaken along the flyway, including sites in the Baltic and
White Sea
as well as the Arctic coast of the
Russian Federation
where the birds breed. The project is carried out in close co-operation with the Institute for Avian Research in
Wilhelmshaven
and the Landscape Ecology Group of the
University
of
Oldenburg
, as well as research groups linked together in the framework of the ESF programme Optimality in Bird Migration including colleagues from institutes of the
Russian Federation
.
