I had the privilege of setting up a nature reserve while I was based in Germany called the Zachariasses which is just outside Lippstadt in Northrhein Westfalen.
During this time we had the first breeding record for an Oystercatcher in the county of Soest. The build their nest on a raft that we had made which was placed some 100m from the shore line. Over a period of time I observed the Oystercatchers tending their young, when I became aware that whenever a bird of Prey appeared the Oystercatcher would give chase.
Nothing new there I hear you say. What was interesting about this was that when a bird of prey appeared be it a Kite, Harrier, or a Goshawk, or even Buzzard the Oystercatcher would chase them all away but up only to the fence line on the edge of the gravel pit.
However, when the Osprey would appear the Oystercatcher would chase it way beyond the fence line in fact on one occasion it chased the osprey for up to 1km away. I wondered way this was, for years this has puzzled me, until a few years ago when it dawned on me.
The Osprey is a fish eating bird and therefore really presents no real treat to the young of the Osytercatcher, it was not about to twist and turn as the other birds of prey did, in order to attempt to get the young from their nest. So, it was in the interest of the Oystercatcher to stay as close to its young as possible when the other birds of prey where around.
If you have another ideas I would be interested to hear them.