gulls at parking lots

in the morning, frequently i see gulls at parking lots. many of them.
some have ideas on why, as you can see on the attached link:
https://www.google.ca/search?hl=en&s....0.-G4o8yM6F0s

but i see that they stand there doing nothing, for several minutes. frozen.
just today arrived 10 minutes before the store opens, so i watched them. they are not socializing. just freeze.
sometimes hundreds of them. no noise. then, after a long time, 1 decides to take off. then another. sometimes all go.
so i began to think that must be a reason for that strange behaviour.
lets see:
1-they are not there for food.
2-they dont deal with 1 another
3-they spend considerable time sitting there still
must be something they find at the parking lot.
parking lots are covered with asphalt.
could it be that the asphalt warms up and keep the warmth better that the surroundings, and this way they warm up and makes flying easier?
it is the only thing that occurs to me.
it was at a large parking lot of a sports arena where i used to fly my small park fliers at dawn that i witnessed 1 of the strangest situations.
i was flying 1 of my small foamy planes fashioned after a gull and testing a new gearbox. that day there were over 1 hundred of them.
everytime i launched it, several gulls took off and followed it closely, and when i stopped the motor they left. then i noticed that the gearbox made a high pitch sound. barely perceptible to me, but that could sound to them as a cry or something and they approached the plane trying to learn what was that about. i think there is a short video at my blog showing that.
but could be another reason for them to gather there quietly.
any1?
the plane mentioned is at page 13 of my blog