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Results of the field survey performed daily in 1978, 1981, 2004, 2005 and 2007, every two days in 1979, 1980, and every 3 days in 2010 and 2011. In 2007, the field survey was performed from 11 May to 6 June but the data from 31 May to 4 June is missing. The period between the 2 dashed red lines indicates the emigration period.
