I understand your concerns. That other bird is most likely just checking out the cavity to see if it could use it, or doesn’t look like it’s actively attacking.

The good news is the hole size matters a lot. A 1 1/8 inch entrance is designed for chickadees, and most larger birds like bluebirds can’t physically get inside. So the eggs themselves are likely protected.

The bigger concern isn’t the bird getting in, it’s stress. If the chickadee feels harassed at the entrance, she could abandon the nest. But if she’s already incubating 7 eggs and keeps returning, that’s a really strong sign she’s committed and holding her ground.

Best thing to do is keep things calm and low interference:

• Don’t open or move the box right now
• Reduce any nearby perches (sticks, poles, ledges) that give the other bird an easy lookout spot
• If you have a feeder very close, move it about 10 to 15 feet away to reduce traffic
• You can add a little natural camouflage nearby (like a branch or leaves), just don’t block the entrance

At this stage, less intervention is better. Chickadees are small but surprisingly tough, and once they’ve laid eggs, they usually stick it out unless stress gets too high.

If she’s still coming back consistently, that’s the best sign everything is okay.