FAT RESERVES AND BODY MASS IN SOME PASSERINES MIGRATING IN AUTUMN THROUGH THE SOUTHERN BALTIC COAST Marta cis³owska and Przemys³aw Busse ABSTRACT cis³owska M., Busse P. 2005. Fat reserves and body mass in some passerines migrating in autumn through the southern Baltic coast. Ring 27, 1: 3-31. The aim of the present paper is to serve with a huge data set on the fat and body mass of birds that have been caught during the field work of the Operation Baltic since 1983 (earlier data are still not available in a digitalised form). There are given fat score valuations of 38 species and correction factors for the body mass standardisation. Some comments on ob- served fat scores in species of different migratory habits are added. They should encourage students to continue the research process on a wider scale. Key words: fat reserves, body mass, autumn migration, passerines INTRODUCTION As one of the interesting aspects of the bird migration research since many years one may consider studies on body mass changes and fattening process in the course of migration (McCabe 1943; Wolfson 1945; Helms and Drury 1960; Blumental and Dolnik 1962; Dolnik and Blumental 1964; Blumental 1967; Dolnik 1967a, 1967b; Busse 1970 and so on). The process runs both during real migration of an individual and during cage life of a bird belonging to migratory population. This last charac- teristic shows that the process is controlled by endogenous, inherited program that bases on internal biological clock. Non-migratory species do not show such cyclic changes in fat deposition or the process is clearly different and related to other than migration phenomena (Berthold 1993). Fat reserves are basic stores of energy that is necessary to perform migration  lipids are the most energetic molecules that can be stored in the bird body. The fat reserves are distributed in different parts of the body, but as much as half of the whole stored fat can be located just under the skin, M. cis³owska, P. Busse (corresponding author), Bird Migration Research Station, University of Gdañsk, Przebendowo, PL-84-210 Choczewo, Poland; E-mail: busse@univ.gda.pl Publication appointed to the SE European Bird Migration Network papers