Meeting Abstract

43.5  Thursday, Jan. 5  Migration in three dimensions: Flight altitudes of small migratory birds BOWLIN, M.S.*; ENSTROM, D.A.; COCHRAN, W.W.; COCHRAN, J.; Univ. of Michgan-Dearborn; Illinois Natural History Survey; Illinois Natural History Survey; JDJC Corp.

Small migratory birds use approximately one third of their energy budget during migration on flight; most of the mortality that these animals experience may also be concentrated in this phase of the annual cycle. Yet, we know very little about the behavioral ecology of small migrants during their nocturnal flights. Here, we present data we have gathered from ~35g Swainson’s Thrushes (Catharus ustulatus) carrying newly-developed 1g altitude transmitters. With altitude readings every 30s during the migratory flights of birds followed from takeoff to landing, our tracks represent the most complete data set about the flight altitudes of individual passerine birds collected to date. Surprisingly, the birds did not all adopt an energetically efficient strategy of ascending, leveling off, and then descending; instead, some repeatedly gained and lost over 60% of their maximum altitude. We will present these data and discuss our initial efforts to correlate this intra-individual variation in flight altitude with variables such as light pollution and wingbeat frequency.