When we moved into our house in Boulder, it had been empty for some while. During that time, a mated pair of barn swallows had built a nest over our front porch light. A couple of weeks after we moved in, we noticed tiny heads popping out of the nest. We watched as the parents would feed their chicks, and finally, a month after we moved in, all three were big enough to see over the brim of the nest.
I got a surprise right after I took this image: all three chicks flew out of the nest! They are already expert fliers; swallows catch insects on the fly, and can turn rapidly in flight. This was proven to me by the parents, who are very protective of their chicks. When I stand near the nest, the parents fly circles above my head and dive in, only to veer away when they are a few inches from impact. It's pretty impressive. They also sit on the eave a few feet away and chirp madly when I'm there. It's supposed to scare me away, but it's so darned cute!