No compensatory fuelling due to late autumn migration in the Garden Warbler Sylvia borin

Birds migrating late in the migration season may need to compensate for the late departure by increasing migration speed. To increase migration speed late migrants should depart from stopovers along the route with larger fuel loads than early migrants. Both higher migration speeds and increasing fuel loads with the progress of the season have been reported in the literature. Here we test if Garden Warblers (Sylvia borin) show different fuelling strategies when captured on migration in the early or late part of autumn migration and given unlimited access to food. We also included a group of birds that were captured early in the season but held under a light regime with shorter day lengths to simulate thirty days advancement in time. We found no difference in maximum body mass between the groups and all groups reached fairly large fuel loads (mean: 39.2 % of lean body mass). Maximum fuel load was also strongly correlated with fuel deposition rate and this may suggest that Garden Warblers migrate at high speed during the entire season, which leaves little room for increasing speed later in the season.

Fransson, Thord (författare)
Jakobsson, SvenStockholms universitet,Avdelningen för etologi(Swepub:su)sven (författare)
Kullberg, CeciliaStockholms universitet,Avdelningen för etologi(Swepub:su)ckull (författare)
Stockholms universitetAvdelningen för etologi (creator_code:org_t)

Av författaren/redakt...: Stach, Robert, 1 ...; Fransson, Thord; Jakobsson, Sven; Kullberg, Cecili ...

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