Katharina,
It looks like a Chickadee to me.
Paul
From: Katharina Bergdoll (Redacted sender "trineberg2002" for DMARC)
Sent: Monday, May 7, 2018 7:58 AM
To: Nnasnet
Subject: [nnasnet] Can anyone ID Eggs/nest??
This in a new box in marsh near Newton's Pond..
Katharina Bergdoll
watershed address: Newton's Pond>Beales Mill Run>Nomini Creek>Potomac
River>Chesapeake Bay>Atlantic Ocean