Craneworld - Resumés: 7.3 Resumé 2003: Acoustic individual monitoring over six years

Results (1): identification of crane individuals / pairs

n important new finding for grus grus is that it is not the female initiating the unison call, but always the male. The male starts with 2 less intensive short tones of lower, increasing frequency, after which the first high and loud call of the female is expressed, fig. 1, often at a slightly higher frequency than her following (shorter) calls. The male answers this first female call with a first loud and longer call, which may be the reason why earlier researchers believed that the female is initiating the unison call, deceived by the low intensity of the introductory sequence and the low sensitivity of their equipment.

The basic questions for the individual recognition to begin with were (a) do the crane pairs call diferent enough to be differentiated? (b) do they call stable and reproducible enough to be recognised in later weeks and years?

Therefore, unison calls, with which Eurasian Cranes often begin the day even before dusk, were recorded in the morning, or in the evening, when defending their territory against other cranes, and during courtship. Also guard and flight calls, and also some other communication expressions were taken. In 1998, about 200 files from 7 pairs in their territories and outside of it, one adult unpaired male, and a few calls of unpaired youngsters, most of which were of analysable quality, had been recorded from late March to May.

The main result is that - although there are variations between the calls - the sonogram and the "voiceprint" for a given pairs are stable, reproducible and can be safely recognised by comparing the intensity maxima and minima at characteristic frequencies.