Typically, when you see a nestling at the cavity opening (top right photo) it’s ready to fledge in 3 days or less. The adults will decrease their feeding frequency to lure the young birds up into the opening and eventually out of the nest cavity. Both parents continue to care for the young for about 3-4 weeks after they fledge.
Note the red feathers on the forehead of the nestling (top right photo). Then notice the red feathers on the crown of the juvenile in the main photo. Finally, on the adult (lower right photo) the bright red patch is on the nape. From nestling to adult, the red patch moves back as it ages, sort of like a conveyor belt. -This is true for the males only. Female nestlings may have a few red feathers on the forehead, but they will soon molt away.
Secondary cavity nesters rely on woodpeckers’ old cavities, like the Bewick’s Wren, Chestnut-backed Chickadee and many other birds. While these birds can perform some amount of excavation, they are typically unable to create an entire nest cavity on their own.
Small mammals, like the Townsends’ Chipmunk, may also benefit from an abandoned woodpecker cavity, using it for a den.