I have twice now observed a loose flock of small gulls flying inland some two or three kilometres from the beach, calling constantly, and climbing to a considerable height. On each occasion it occurred before midday local time, and their flight was highly directional, eg. flying in a straight line. Then, on both occasions the flock suddenly turned 180 degrees as one, so that stragglers on the outward journey became leaders on the return, again in a straight line back towards where they had come. They their flight profile changed and instead of climbing they adopted a gentle decent which caused them to gain speed rapidly so that they had to angle their wings like falcons might, and they ceased calling. Then silently, but for the hiss of air past their wings they set off for home at record speed.

There was no evidence of feeding behavior in either direction, and none of the slow random movements associated with feeding on high altitude moths or other food items. It appears to be social behavior, and seems to involve flying just for the thrill of it! Do you have a scientific explanation for these observations?

Difficult to give a definitive answer to this one. Gulls are social animals and relatively intelligent so I would not like to hazard a guess at the motivation for a specific flight patter. It could be that there was a possibility of a food resource inland and the calling was related to this, but that after gaining height and distance towards it this turned out to be a bust and the group went home! This is  - of course - pure speculation.

In fact there is quite a lot of computer-based simulation work on bird flocking and fish shoaling that indicates complex behavioural patterns at a group level could easily emerge from very simple decision making rules. this will give you a brief explanation

http://en.wikipedia.org/wiki/Flocking_(behavior)

So something worth bearing in mind is that apparently complex and organised group behaviours such as those you say could be a consequence of simple decision rules that have evolved under natural selection - in other words there may not need to be a rational explanation for what you saw in terms of a "pay off" for the birds that is motivating the behaviour.  Although the issue of how to quantify and test animal emotions is also problematic - your suggestion that the gulls just "enjoyed" the thrill of the flight is also quite possible. Certainly play is widespread in animals (and humans) so we shouldn't discount an emotional motivation (i.e. making themselves happy).