There’s no bird in this post, but something that birds encounter often: a termite nest high in a tree. This one is in Manly Dam National Park, near Sydney, Australia:

Termites that build nests in trees are called arboreal termites. They carry mud up the tree and use it to build their nests, which can grow rather large, like this one. I’ve come across tunnels of mud that run across roads and up trees. The termites build the tunnels for protection from the sun and from scavenging creatures. The termites usually also have underground tunnels.

Here’s a closer view of the same nest:

When the nests are old and abandoned, birds like kookaburras will dig holes in them and use them as homes.