Ardea
Official journal of the Netherlands Ornithologists' Union

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Van Eerden M.R. & Gregersen J. (1995) Long-term changes in the northwest European population of Cormorants Phalacrocorax carbo sinensis. ARDEA 83 (1): 61-79
The current expansion (1978-1993) in the number of breeding Cormorants in NW Europe resulted in an annual increase rate of 16.3%. Recently indications of a decline in growth rate have become apparent. With their large waterbodies Denmark and The Netherlands form the stronghold for the population (94%). The expansion of numbers and range extension was faster in Denmark than in The Netherlands which correlated with a higher average young production. The density of breeding Cormorants in relation to the fishing grounds available was highest in the small scaled, eutrophicated, freshwater habitat of the Dutch provinces of Friesland and Overijssel ( > 25 pairs/km-2). At large freshwater lakes as IJsselmeer and along the large rivers lower densities were recorded (7-15 pairs/km-2). The Danish waters are considered to be to a large extent undersatiated with respect to the number of Cormorants ( > 5 pairs/km-2). Several colonies located in trees counted over 2000 pairs (11% of all colonies which harboured 65% of all breeding pairs in 1992). Maximum colony size so far was recorded at Oostvaardersplassen (The Netherlands, Flevoland 1992, 8380 nests) and Braendegard (Denmark, Fyn 1992, 7087 nests). It is concluded that, although feed-back mechanisms in the oldest colonies may cause a stabilisation and even a local decline in numbers, the overall population still continues to explore new, previously unoccupied habitat. Extrapolation of the number of breeding pairs into the future was made in relation to the area of feeding grounds available and provided a conservative estimate of 103300 breeding pairs, compared to 60331 pairs in 1993.


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