Patch choice of avian herbivores along a migration trajectory–From Temperate to Arctic |
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Authors: | AJ van der Graaf J Stahl GF Veen RM Havinga RH Drent |
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Institution: | aAnimal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, P.O. Box 14, 9750AA Haren, The Netherlands;bLandscape Ecology Group, University of Oldenburg, 26111 Oldenburg, Germany;cCommunity and Conservation Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, P.O.Box 14, 9750AA Haren, The Netherlands |
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Abstract: | Migratory waterfowl species seem to track temporal and spatial pulses of optimal forage availability on their way from temperate wintering to arctic breeding sites. In order to unravel the relative contribution of forage quality and forage biomass to foraging choices in avian herbivores, we experimentally manipulated biomass and quality of main forage plants through fertilisation and grazing exclusion at three sites along the flyway of barnacle geese, Branta leucopsis. Fertilisation increased the nitrogen content of the forage and grazing exclusion increased biomass levels. Manipulated plots were offered to wild geese in a random block experimental design and goose visitation was measured through dropping counts. At all sites there was a trend towards a higher preference of plots with increased quality and average biomass above plots with an average quality and increased biomass. Generally, geese preferred plots with highest standing crop of nitrogen. The numerical response of the geese to forage changes was supported by behavioural observations at the Baltic site. We conclude that for migrating barnacle geese the bottlenecks in the standing crop of nitrogen appear to lie in the limited biomass availability at the Baltic stopover site and the limited nutrient content of food in the Arctic breeding site, restricting the potential nutrient intake on these sites. |
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Keywords: | Barnacle goose Branta leucopsis Flyway Forage quality Grazing experiment Plant biomass Plant– herbivore interactions Salt marsh |
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