It is likely that shortening daylight hours is the signal to head south. Males often leave up to two weeks before the females, and they are the first to return in the spring. The last ones through in the fall are late-nesting females and their young. They need all the help they can get to complete the journey. If feeders are taken down too soon, many of them will not make it.
Male hummingbirds lead a carefree life.
They do not assist with nest building, incubation of eggs or feeding the babies. All of this work is done by the female. She builds the nest of soft plant material and other downy fibers, such as cottonwood fluff. It is usually held together with strong lightweight spider web, or horse hair. The nest is camouflaged with bits of lichen, bark or leaves.