Setting harness sizes and other marking techniques for a falcon with strong sexual dimorphism

Backpack radio-tags can be used to monitor survival of raptors for several years after fledging, but may reduce survival if a poor fit results from su bjective judgments. We present an attachment method that can use bird measu rements to predict harness sizes. Relationships between body mass of Saker Falcons and harness size predicted the size for smaller falcon species. Har nesses were fitted when birds had reached full size in the nest, which requ ired age estimation at a previous visit to predict a fledging date. Equatio ns based on wing length provided objective aging of nestlings. A pump-press ured water gun aided capture of young falcons and toggle-loops restrained t he feet during marking. Saker Falcons with radio-tags and others marked onl y with leg bands and implanted transponders had the same recapture rate (7% ) in autumn, indicating similar survival. This retrap rate should be adequa te to estimate harvest rates and population sizes for Saker Falcons.