But where do they come from? And how do they know? Are there gull scouts? Here's my first furrow after lunch:
"Because winds are stronger at higher altitudes - so less energy-expending flapping is required - gulls are often thousands of feet in the air. From such a vast height, and by using their keen eyesight, they have an excellent all-round view for many miles around. This allows them to exploit potential feeding opportunities very quickly."
Once upon a time, Farmer Humph very nearly ran over a gull; but that's a story I'm saving for another day.