Related Clues:

• Places for eggs
• Things built by cranes
• Homes of 15-Acrosses
• Wrens' homes
• Abodes for birds
• Homes on limbs
• Emulates a matryoshka doll, save one
• Wasps' dwellings
• Arboreal digs
• Retreats for robins
• Common sources of tweets
• Stacks like matryoshka dolls
• Birds' homes in trees
• 42-Down holders
• Comfy quarters