Ardea
Official journal of the Netherlands Ornithologists' Union

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Madsen J. (2001) Spring migration strategies in Pink-footed Geese Anser brachyrhynchus and consequences for spring fattening and fecundity. ARDEA 89 (1): 43-55
Individual variation in spring migration strategies was analysed for neck-banded Pink-footed Geese Anser brachyrhynchus migrating from Denmark (D) via stopover sites in the Trondheimsfjord area (T) in mid-Norway and Vesteralen (V) in northern Norway to the breeding grounds in Svalbard, 1990-97. Body condition of marked individuals was assessed by use of an abdominal profile index before departure from Denmark and before migration from Vesteralen where the majority of geese stop before departure to Svalbard. Breeding success of marked individuals was registered during the subsequent autumn. Since the late 1980s, Trondheimsfjord has developed as a new stopover site, supplementary to the traditional areas in Vesteralen. During the 1990s, first arrivals in Trondheimsfjord progressed from late to mid April, but mass arrival was stable. First arrivals in Vesteralen progressed from early May to late April. Marked individuals were categorised into five migration strategies, ranging from early departing geese from Denmark making extensive use of Trondheimsfjord and only stopping shortly in Vesteralen (new strategy) to late departures from Denmark migrating directly to Vesteralen (traditional strategy). Throughout 1990-97, the majority of marked individuals were departing late from Denmark, but the majority stopped in both Trondheimsfjord and Vesteralen. Use of migration strategy was not related to age, sex, social status or body condition prior to migration to Norway, but was affected by previous strategy. Almost all geese using early strategies and relying only on Trondheimsfjord as stopover changed strategy in the following spring, whereas only 26-37% of the late departing geese using both Trondheimsfjord and Vesteralen or only Vesteralen changed strategy in the following spring. All geese leaving for final migration in poor body condition changed strategy in the following spring, whereas birds leaving in good condition were less likely to change. Geese using early strategies and relying on Trondheimsfjord as stopover left for final migration in significantly poorer condition than early birds using both Trondheimsfjord and Vesteralen and late birds using Trondheimsfjord and Vesteralen or only Vesteralen. In 1991 and 1996, early D-T's and late D-T's bred less successfully than birds using other strategies. In the other years, the tendencies were similar but not significant. The results suggest that there was a fitness cost attributed to the use of early strategies and reliance on Trondheimsfjord as stopover. The finding that geese switch between strategies, probably in response to previous experience with accumulation of body stores, suggests that they explore environmental conditions to adopt an optimal migration strategy and that they are still 'testing' Trondheimsfjord as a stopover site


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