Wat doen watervogels als er ijs ligt?
Drentse vogels , Volume 23 - Issue 1 p. 72- 81
Waterbirds are yearly counted simultaneously in mid-January in the whole province of Drenthe. In 2008 there was no ice cover, but in 2009 most waters, even larger lakes were completely covered with ice. Most ducks and Cormorants had lower numbers in 2009 (Table 1), but herons, swans, geese and gulls increased with ice cover. Some of these species were probably local birds, but some, like the gulls might have migrated into the area from northern areas. Decreasing numbers were most clear in narrow and shallow waters en least clear (even slight increase) in large lakes (Table 2).
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