Individually characteristic corncrake Crex crex song reveals long-distance movements within the breeding season
MetadataVis full innførsel
- Master's theses (INA) 
Due to modern agricultural practices, the corncrake is a species of global conservation concern. Mowing of meadows may cause corncrakes to make movements within one breeding season, but such movements are in general poorly understood. Previous studies have shown that corncrake calls are individually characteristic, and also that variation in individual song characteristics on a large geographic scale (>100 km) may occur. Song recordings were therefore used to identify both corncrake movements and possible differences between the corncrake populations of E and SW Norway. Observations of singing corncrakes were used to investigate corncrakes’ disappearances from territories: 54 % of corncrakes (n = 80) were found to leave their territories probably or certainly due to mowing. In addition to song recording, telemetry and ringing were also, although to a lesser extent, used to document movements. A total of 32 movements (median = 129 km, range = 0.3 – 404 km) longer than 300 m were found, including 28 movements found by discriminant analyses of individual song characteristics (probability ≥ 0.85), and three movements found by telemetry. A total of 21 individuals were found to make the 32 movements, which included 22 long-distance movements longer than 17 km - all found by individual song characteristics, and 18 movements longer than 100 km. A total of six individuals were found to make more than one movement. A total of 18 movements, including ten long-distance movements, had a probability ≥ 0.95. Individual song characteristics showed no evidence for the two Norwegian corncrake populations to be different; and 13 movements between E and SW Norway also implies that the populations are functionally connected, even though they are about 300 km apart. Presumably 60 different corncrakes were recorded, but due to movements the actual number of corncrakes being recorded was found to be 36; we therefore suggest that the 2009 Norwegian corncrake population was strongly overestimated. To avoid such overestimation we suggest that future population estimates should be based on observations done prior to 16 June, where observations which are less than one km from each other and potentially the same individual, only should be used once in estimates. Using these restrictions, the 2009 Norwegian corncrake population estimate would have been about 123 individuals, which is 39 % lower than the official population estimate of 200 individuals. Our results show that recording of corncrake song might be an effective method to study corncrake movements; the method has shown that movements by Norwegian corncrakes seem to be a common phenomenon. På grunn av moderne landbruksmetoder er åkerriksa en art som krever et globalt bevaringshensyn. Slått av enger kan medføre at åkerrikser gjør forflytninger innen én hekkesesong, men slike forflytninger er generelt dårlig forstått. Foregående undersøkelser har vist at åkerriksesang er individuelt karakteristisk, og at variasjonen i individuelle sangkarakteristikker kan forekomme på stor geografisk skala (>100 km). Sangopptak ble derfor brukt til både å identifisere åkerrikseforflytninger, samt å finne eventuelle forskjeller metoden har vist at forflytninger blant norske åkerrikser synes å være et vanlig fenomen.