I don't think I ever knowingly noticed birds feeding on them. The ones I was considering where the 'Pepper-Pots' simple yellow flower and a seed pod about the size of a golf ball, large 12" leaves plus 'cabbage type leaves under the water'....I tend to think these are our native species but I am only assuming that as they seem to be the most common wild ones.....the smaller fancier double flowers I think are generally ornamental (at least in this country) I do know the bigger floating 'Pepper-Pot' leaves are loved by pond snails both for eating and breeding on Carp, Bream, Rudd and even Tench are often seen 'surfacing' under them, people think they are just sheltering form the glare of the sun but if you watch the fish are actually moving from leaf to leaf eating Snails etc. The 'cabbage' or softer sub- surface leaves are eaten by Swans and Geese. The smaller lilies (though this is only my own observation) do not seem to be touched until the leaves and flowers actually start to break down and rot and I know early winter I can pull rake loads of rotting smaller leaves and stalks out of the ponds but most of the larger ones are gone until next year.....the large tubers/roots of the Pepper-Pots are also very much appreciated by worms in the muck heaps too... weather any of these observations are any indication to how edible and safe the two 'types' are is anyone's guess though.
D.B.