you can either see them in the mangroves on eastern corniche/salam or sometimes they are in the mangroves off mussafah road, but they also can be seen along by al ain truck road/al wathba, also if you head towards mirfa they can be seen along the roads there.
There is a flock of them in the Mangroves - we didn't see them every time we kayaked through, but mostly. We have also seen them in the channel between Mangove Village and Mussafa, as it opens out into the sea.
Happy spotting - but you'll need a good zoom, they don't allow anyone to get close.