juvenile or adult?

These two Northern Cardinals Cardinalis cardinalis look alike.  Both are females, so have some red feathers like the all-red males, but are mostly tan rusty brownish so they can hide better from predators in nesting season.

But notice the difference between the adult and juvenile?

The young first-year female Cardinal above still has her juvenile dark grey bill.  Her new adult feathers are just coming in to form her winter coat.

The adult female Cardinal at right is identified by her bright orange or red bill.  Her feathers look disorganized like her youngster because she is molting.  She loses her old worn feathers in late summer, so her new warm winter feathers are just growing in.