On Sat, 2 Apr 2011 14:54:56 EDT, nik Simpson wrote:

I'm inclined to think just a stealthy blue Heron, though I can't rule
aliens out.

Herons are aliens, aren't they?

Last year my son caught one red handed/winged/beak stealing one of our koi
on webcam. Course it was a night I'd forgotten to turn on the motion
sprinkler. We had a few threaded strings across the pond at the time, but
hadn't put the ones on the fence yet. It landed on the fence, and dropped
right between the wires. Took its sweet time picking one out too,
thankfully only one. Funny thing, when I went out that morning, none of koi
seemed at all bothered by the disappearance of their relative. They came up
and ate like nothing was amidst.

More strings were put up and we don't forget the motion sprinkler. The
fence was redone this spring and string was put up as soon as it was done
so the dang bird can't land. ~ jan
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Zone 7a, SE Washington State
Ponds: www.jjspond.us