Heron using bait for fishing

["Philip Veerman" <>]

David Attenborough in one or more of his very good nature documentaries 
promulgated film of this very behaviour by (presumably) another species of 
small heron. So it occurs in different species. Trouble with the film being so 
famous is that it begs the question as to how widespread the behaviour actually 
is. Or do we just think it is commonplace? How many species do it, on how many 
continents? Is it learned or instinctive? Is it very rare and yet very well 
known just because one bird learned to do it.
Philip