Nesting Box

[maggiebee]

Decided to clean out my nest box today. Bluetits raised a family of at least three. Sadly there were two unhatched eggs in the nest. Not quite sure what happened to these. Any ideas?

[friedgreentomato]

I think my dad used to call these 'blow' eggs - they just don't develop.

[Chipchopper]

This seems quite common with blue tits that usually have large broods, I've cleaned out many over the years and often found one or two addled ones that failed to develop.