Differential migration of juvenile and adult Grey Plovers Pluvialis squatarola at the mouth of the Vistula River, Poland

Abstrakti

Ringing data of 130 juvenile and 65 adult Grey Plovers caught between mid-July and mid-October at the mouth of the Vistula River, Poland, in the years 1983-1996 allowed timing and description of a differential migration between these two age classes. Body mass did not vary during the whole period of passage in adults, averaging relatively low values, while an increase in mass towards the end of migration was observed in juveniles. An age-related site exploitation was suggested to explain different daily trapping patterns . Most of the migrating adults had not yet started primary moult, and only 11 % were in, or very close to, suspension stages of innermost feathers .