'poor little thing', you big softy lady j. We used to have roast sparrow, when I were a nipper, and fought over the legs.
It amazes me we don't see loads of dead birds littering the floor. Do cats(and things) eat them all?
Are there more birds than people in Britain/the world?
Do we know how many?
How long does the average bird live?
Hope you don't mind me 'invading' your post, milady. x
To answer your Q....yes, it most likely drowned, garden birds don't swim and if they misjudge the water depth they panic when their feet don't touch the bottom (I know the feeling :)). If birds can drown so can other wildlife so ponds need to have a shallow sloping side, flat leaved floating plants or a ramp made from large stones or wood to help them escape.