Swallow using tail feathers as third leg

I've been photographing a nest and nestlings for two weeks now and have noticed how the parents balance themselves at the nest by 'glueing' their tail to the nest or wall. The feathers get quite damaged in this way and the fork of this one has nearly been worn away. One of the four nestlings has flown and was perching on a pipe nearby but getting its fair share of the food from the adults.

A couple more pics here