Ardea
Official journal of the Netherlands Ornithologists' Union

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Braaksma S. (1958) Aanvullende gegevens over de stand van de Roerdomp, Botaurus stellarus L., als broedvogel in Nederland. ARDEA 46 (3-4): 158-166
An investigation concerning the distribution of the Bittern, Botaurus stellaris L., in the Netherlands during 1950-1953 proved that Bitterns were breeding in at least 280 localities. The average number of annual breeding cases during this period was probably somewhat higher and may be estimated at about 300-330. As a result of the publication of the investigation results in 1954 (Braaksma etc., 1954), many reactions of amateur ornithologists reached the Department for Nature Protection of the State Forestry Service. Several letters contained further data, partly from still unknown breeding localities, concerning the distribution of this interesting species. In addition to these our own personal gathered a good deal of information on the occurrence of the species in areas which in 1954 were mentioned as doubtful breeding grounds. Though the greater part of the information is rather incidental, the new facts gathered seem to lead to the following conclusions. In the: first place it can be estimated that Bitterns are very much attached to their once selected breeding grounds. We are practically certain that Bitterns leave their habitat only when this disappears completely, or when it is changed in a radical manner, for instance by drainage, cultivation or continued disturbance. The total average number of breeding cases during the period of 1950-1957 was probably somewhat higher than is indicated in 1954 and can be estimated at about 320-350. Owing to some new settlements of Bitterns in the existing nature reservations and the establishment of new breeding sanctuaries, the number of Bitterns breeding in reservations can at present be estimated at about 20 to 25% of the total number of breeding Bitterns in the Netherlands. The severe winter of 1955-1956 probably caused the death of 80-150 Bitterns in this country. It seems likely that most of these birds belonged to the population of northern or eastern countries, as banding records seem to prove the suggestion that probably at least 75% of the Dutch Bitterns used to pass the winter in southern countries. The severe winter does not seem to have caused serious losses to our own population. It seems likely that should no extensive marshy areas be available, the Bitterns are more and more inclined to accept smaller fens. Perhaps therefore the future does not seem to be as precarious as has been suggested in 1954.


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