Why some birds are now singing BEFORE the crack of dawn

In a word (actually two); light pollution. It's the widespread use of intense artificial light when there should be darkness.

American Robin

According to a recent study, American Robins may start to sing 30-minutes to 3 hours earlier than they did in the past. The birds, quite simply, are confused. It's also evident in Mockingbirds, Wrens...all species. We can't see stars (or comets, meteor showers - all that neat stuff) in the night sky for the same reason - light pollution.

The Eastern Screech Owl is fairly common here in north Texas, and it "nests" throughout cooler weather - starting now. However, Screech Owls don't actually build nests. They simply find a safe place (unused birdhouse, old woodpecker hole, rotted-out tree trunk etc.) and lay eggs there.  The criteria are that it be hidden (so the owls can sleep during the day), the entry is at least 3 inches in diameter and the eggs won't just roll away.

In extreme weather the smallish owls may seek shelter in such a place (called "roosting"). If so, they're inclined to lay eggs there too.