When it comes time for swallows to migrate south in the fall, swallows gather into flocks just like most other bird species. However, unlike most bird species, theur flocks can be gigantic... sometimes containing thousands of birds. They swoop and fly in a huge cloud covering much of the sky. The sight gets even more magnificent when the group reaches a large body of water. These bird eat, drink, and yes, even bathe while in flight. Upon reaching a lake, the birds simultaneously swoop down, skimming right over the waters surface, dipping in their bills for a drink, causing thousands of tiny little ripples to form beneath the flock. The birds even plunge entirely into the water, flapping their wings and allowing the water to soak in between their feathers. This is how they bathe.
Though swallows do not fly in formation like geese do when in flight, they do fly as a group. Wherever the lead birds go, the other's follow, much like the famed starling flocks which often cause a stir of excitement. However, these birds do not do the incredible job of sticking together like on big cloud. Each one swoops their own way, appearing as a confusing swarm of birds all darting this way and that, but at the end of the day, all of them end up at the same place as the rest of the flock by roosting time that nights. The swallows then literally cover the treetops, as thousands of them prepare for the night.