They were like boxes made of shells, the work of a patient hand.
A comparison offers here.

Certain Australian birds, notably the Bower-birds, build themselves covered walks, or playhouses, with interwoven twigs, and decorate the two entrances to the portico by strewing the threshold with anything that they can find in the shape of glittering, polished, or bright-coloured objects.

Every door-sill is a cabinet of curiosities where the collector gathers smooth pebbles, variegated shells, empty snail-shells, parrot's feathers, bones that have come to look like sticks of ivory.

The odds and ends mislaid by man find a home in the bird's museum, where we see pipe-stems, metal buttons, strips of cotton stuff and stone axe-heads.
The collection at either entrance to the bower is large enough to fill half a bushel.

As these objects are of no use to the bird, its only motive for accumulating them must be an art-lover's hobby.