Mulhauser, B. & J.-L. Zimmermann
(* = Kurzbeitrag)
Individuelle Erkennung und Bestandserfassung bei der Waldschnepfe Scolopax rusticola anhand von Gesangsmerkmalen balzender Männchen.
(von 1994 bis 2006 vergeben)
Stimme, Sonagramm, Balzstrophe, Lautäusserung, Individuelle Bestimmung, Bestandserfassung
Schweiz, Frankreich, Jura, Neuenburg, L’Auberson, Waadt, Jougne, Doubs
Individual recognition and monitoring of male Eurasian Woodcocks Scolopax rusticola by characteristics of their roding calls. Taking a census of the woodcock population during the breeding season is a recurrent problem. Indeed, how to count birds during their displaying flight when the observer stays in a fixed point? The key to this problem is the identification of individual Woodcock male by characteristics of their songs. From 2002 to 2006, thousands of sonagrams have been recorded in one roding area in the Jura mountains in order to determine the best way of identifying individuals. To test it, a second site has been investigated in 2006.
The graphic analysis of sonagrams shows that the melody is made up of two to six deep elements (low frequency notes), the «row», and one shrill, the «tsip» (high frequency note). Each male has its own song with a precise number of deep notes. We have tested five temporal variables on the «tsip» and/or the «rows» permitting to identify each male.
Tests of vocal stability over time have been based on 11 well-known woodcocks. This stability is excellent for the variable E (length of the sound «tsip» at 4.5 kHz, coefficient of variation cv < 5 %) and good for two others (cv < 7%). A standardized method for identifying individuals can be proposed.
But some precautions have to be taken when applying this quantitative census. The correlation between the number of contacts (Nc) and the number of male (Nm) has been calculated in different areas of the Jura mountains (France and Switzerland) and in Poland and compared with two additional studies published in France and England. The conclusion is that each site shows an excellent linear correlation between Nc and Nm, but the slope of the regression line is changing from one year to all others at the same site and from one site to another. So, an overall mathematic formula based on a fixed ratio of Nc/Nm is impossible to apply. The conclusion is that we cannot use the number of contacts Nc during an observation session to determine population size. In order to count the number of male in a listening station, the sole manner is to proceed with recordings of the roding calls of the woodcocks from year to year.
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