I have two bird boxes in my backyard, both made by us so not the greatest job. Chickadees have successfully nested in one of the boxes three years in a row. The other box was supposed to be for swallows but they've never shown any interest in it. We attempted to make the diamond shaped opening for them to keep their house sparrows out.

What I was seeing today are black-capped chickadees on each box, both of them were hammering at the entrance. I know for one of them the hole is large enough since we've had them nest for three years in a row.

My question: is this instinctive behavior to attempt to enlarge the hole even though it is already large enough?

Deborah West
Olympia

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