An automated system for the measurement of mass and identification of birds at perches

Studies on small wintering birds often monitor body mass variation over day s or seasons. Typically, birds are weighed manually or data are obtained us ing an electronic balance which displays the bird's mass during visits to a feeder. The problem with these techniques is that they require the manipul ation of the animals and/or are labor intensive. We built an automated syst em which combines a transponder-based radio identification device (RID) and an electronic balance fitted with a weighing perch. This setup permits dai ly mass variation in birds to be monitored automatically without human pres ence. The system provides reliable estimates of inert masses (r(2) = 1). We also used it to monitor bird masses in an aviary. For five days birds were caught periodically and weighed manually to measure their "real" masses fo r comparison with the system's estimates. Again a strong relationship was f ound between calculated and real masses (r(2) = 0.92 and r(2) = 0.89 using two different balances). This system offers great promise and could be adap ted to many forms of field work.