Kokmeeuwen Larus ridibundus de boom in
Drentse vogels , Volume 9 - Issue 1 p. 24- 24
An adult and two 2nd calender year Black-headed Gulls systematically searched tree tops for caterpillars of Tortrix viridana and Operophtera brumata, while flying against the wind. Both species of caterpillars had an outbreak in May and June 1996, and were pecked from the tree tops after short hovering sessions by the gulls. Every once in a while, the gulls even landed briefly to collect a caterpillar. This procedure was repeated after the gulls had reached the end of the tree line.
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