Body mass, moult and migration speed of the Goldcrest Regulus regulus in relation to the timing of migration at different sites of the migration route

Abstract

We studied body mass, fat reserves and moult data of the Goldcrest Regulus regulus in re-lation to calendar date at three sites along the migration route: Gumbaritsy, NW Russia (south-eastern coast of Lake Ladoga), Kabli, SW Estonia (eastern coast of the Baltic Sea) and Rybachy, Courish Spit (eastern coast of the Baltic Sea, Russia). We analyzed migra-tion speed using ringing data obtained at these stations. The percentage of moulting birds involved in migration was higher in the northern site Gumbaritsy as compared with the southerly site (Kabli). During migration, body mass increased seasonally in the Goldcrests trapped in Gumbaritsy in 2001, but at the more southern trapping sites this trend was absent (Kabli) or recorded only in the later part of migration (Rybachy). Median fat reserves peaked in Gumbaritsy. Migration speed was affected by time pressure (i.e., it increased with date during migration and was more pronounced in the north) and the posi-tion of a certain part of migration route. Migration speed was significantly higher along the routes that crossed the Baltic Sea than at coastal routes. Birds that gained more fat at the time of ringing migrated with a higher speed.