FAT, HYDRATION CONDITION, AND MOLT OF STEPPE BUZZARDS BUTEO-BUTEO-VULPINUS ON SPRING MIGRATION

Physical condition of migrating Steppe Buzzards Buteo buteo vulpinus w as determined during spring migration at Elat, southern Israel, 1 984- 1988. An index based on measurements of body mass, wing-length and cul men was used to estimate fat content, based on fat extraction from nin e buzzards. In addition, hydration condition was measured in 1988 and moult was checked in 1985-1988. More immatures (1001) than adults (459 ) were trapped, and a greater percentage of immatures (19.8%) than adu lts (8.4%) was retrapped during the same season. Adults had significan tly greater fat reserves (4.5% of body mass) than immatures (3.8%). Mo st adults were in some stage of interrupted moult; however, active pri mary moult was noted only in immatures (10%). These findings suggest t hat different age groups use different migration strategies. Most of t he buzzards trapped in this study could not have completed their entir e migration using only stored fat; thus, hunting was probably necessar y to replenish their energy reserves. No indication of water stress wa s found in the spring of 1988.