The smallest of cracks in a tree

A few weeks ago we were pointed in the direction of a Treecreeper’s nest.

It never ceases to amaze me how small a gap these little birds can get into; just a slither of an opening, into the tiniest cavity behind bark. In they flew with beaks full of insects and out they flew with a faecal sac; as fast as lightening, making any chance of a decent photo very limited indeed.
The nest and emergent Treecreeper is pictured below.