Feeding frenzy

On the way home from aqua aerobics today my friends and I were enthralled by the sight of thousands of birds circling, diving, calling, a never ending frantic motion. Unfortunately I only had my cell phone with me so the photo is not the best quality. This photo shows only a small part of the huge flocks - not sure if they were terns or seagulls.
When I got home, some ten minutes later I grabbed my big camera and rushed back, only to find the area deserted, not a bird in sight!! I couldn't even see them flying away in the distance. Amazing. Not sure what fish they were eating, maybe sardines.
We are going to Addo tomorrow. It's my birthday and I can think of no better way of spending it. Hopefully we'll have good sightings....and warmer weather.