Herons: Eyesight?

[JAYS]

How good is a heron's eyesight? A couple of issues occur to me. Firstly as a young bird, fishing for the first time, it has to cope with refraction. The bent stick in water phenomenon. From the heron's point of view the fish is actually not where it appears to be. So does the heron "know" this, or does it have to learn to adjust its aim or go hungry?
I see herons in flight at night over and around the river, quite often. Obviously they can see well enough to navigate in the dark. And I have noticed that this sight seems to be quite acute, in that at 30 yards they will usually spot me and veer away if I move slightly. Even if I am wearing dark clothing and stood under or against river bank trees. It is all very impressive. Maybe they can see well enough to fish at night too? They are certainly often about around first light.

Anyone know whether there is any research available on this that I might read?

[diggleken]

Hi Jays,
I dont know the answer, but I suspect you have done so already in your question - they must learn to cope with refraction or starve.
You cant alter physics in this case so they must adapt.
As with other birds , the nictating membrane of the eye gives them an instant wash after a miss too, so they can go again quickly.
Youre also right in that they do have excellent vision generally.
They are marvellous, coping with water, roosting and breeding in trees and moving around to cope with food supply and weather.
Hopefully someone can be more scientific - maybe try the RSPB or BTO for a discusion paper online?
Ken