James Joseph: Nature (2) The 9-5 life of birds

The other day, as I was sitting outside of my residence hall at 7 in the morning, I began to notice a strange pattern in the birds flying all around and ontop of the buildings. At first glance, they didn't seem strange at all, for they were merely flying around, landing on rooftops, then flying off (which I imagined was because they were migrating north). However, after spending some 2 hours watching them fly all over, I noticed a very similar behavior amongst the birds that we find quite common amongst our fellow humans. It seemed to be that the birds would fly to their perches on top of the rooftops and would wait there. They would just wait. When a larger group of birds were flying by, some of the birds would leave their feathered perch and join the larger group in it's migration forth. Yet there were some birds that had landed on the rooftops at the same time and even earlier than those that had been on the perch. What made it really strange was the fact that the birds on the roof were waiting for particular groups of flying birds to travel with, in the same way we wait at a bus stop with a multitude of other humans, only to get on certain buses that lead to the destination we are expecting to get to. So do birds, similarly to humans, wait at their "bus stops" for their specific rides north? This makes me wonder: How do they know which groups are going where? Do they know certain bird friends in the larger groups that they can identify and go along with, or do they have an innate sense of which group they are supposed to fly with? Or maybe, just maybe, they are waiting for that certain group to go with that will lead them to a more a sacred place, a place that they know and feel is the place they need to go to next?