Strategie wędrówkowe siewkowców (Charadrii) zachodniej Palearktyki

doi:0013-2969

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Title: Strategie wędrówkowe siewkowców (Charadrii) zachodniej Palearktyki

Abstract:

Among Palearctic waders (Charadrii) there are species that winter relatively close to their breeding grounds, as well as those that undertake one of the longest migrations among birds. The majority of them are not able to cross the whole distance between breeding and wintering grounds in one long-distance flight. They divide the migration route into several or even over a dozen of steps between which they stay in areas abounding in food. In stopover sites birds accumulate fat and proteins. Fat is the main source of energy, while proteins indirectly take part in oxidation of fatty acids.Two main migration strategies were defined. Birds that realise the time-minimisation strategy cross long distances accumulating large fat reserves in stopover sites. They reach the destination of migration very quickly, but their total energetic expense on migration is very high due to the high cost of flight with large fat supply. The strategy of energy-minimisation is realised by migration with Iow fat reserves, short stops at stopover sites and short-distance flights. Migration speed is Iow in this case, but also the overall energetic costs of migration are relatively Iow. It was also shown that waders could change the realised migration strategy within a season. The mechanism of the choice of the realised migration strategy acts at the level of individuals. Each bird takes the decision to depart from a stopover site individually on the basis of information coming from the surrounding environment (the quality of a feeding ground, inter- and intraspecific competition for habitat resources, weather, predation pressure), and of its physiological stage (the amount of accumulated fat reserves and the ratę of their accumulation). As these factors at a given stopover site usually influence on many individuals in a similar physiological stage in the same way, a whole flock takes off to the next step of the migration.A bird probably can assess the quality of a feeding ground according to foraging success. Basing on it, the individual takes the decision to depart quickly with Iow fat deposit (energy-minimising strategy) or to stay and accumulate large fat reserves allowing for a long-distance flight (time-minimising strategy). According to the quality of the next feeding site the individual can continue realised strategy or change it. Young birds during their first migration visit by a principle of trial and error many potential feeding grounds. The strategy of minimising the energetic expense allows them for using feeding sites even of a Iow abundance, on condition that such areas are relevantly numerous and they are not too distant from each other.