Was Zugunruhe wirklich ist — eine quantitative Bestimmung mit Hilfe von VideoAufnahmen bei Infrarotlichtbeleuchtung

Summary

In 9 hand-raised Garden Warblers, Zugunruhe was continuously recorded in registration cages with movable perches on microswitches in a constant 12:12 hr light-dark cycle throughout the first fall migratory period. In addition, video-records were taken during 23 nights under infrared illumination involving more than 150 hours. The main results are: (1) infrared illumination did not affect Zugunruhe or other events and thus is a useful method, (2) over 90 % of the Zugunruhe recorded with video is wing whirring (i. e. intense wing beating in a sitting position), the rest is hopping and flying, (3) an interval of the customarily used “half-an-hour-with-Zugunruhe” equals 14.1 min of wing whirring, (4) 35.9 % of the Zugunruhe recorded as wing whirring is missed in a registration cage with one movable perch. This loss is reduced to about 5 % if two movable perches are used, (5) the experimental birds produced in the average 352.1 ± 170.51 (SD) “hours with Zugunruhe” which equals about 165 hrs of wing whirring. When this value is multiplied by the average flight speed of the species during migration (about 25–30 km/h) a theroretical flight distance of about 4800 km is obtained. This is just the distance from the south German breeding grounds via Spain to the estuary of the river Niger which is situated within the center of the population-specific winter quarters. Zugunruhe in that species thus appears with some restrictions to be “wandering by wing whirring in a sitting position”.