Typically they cling to branches or cave formations loosely and with their whole bodies, like spidery bats. It's not uncommon to find one holding on to the back of one's shirt at night, going for a ride. They only roost "at prayer" to breed, and each particular applause of handbirds will breed among itself once a year. They will stay clasped like this for a month unless threatened, at which point they give flight and drop their eggs.
Now a handbird egg is like a fine opal and can fetch a tidy sum from a gem merchant. These eggs have a 25% chance of being inert, a 25% chance of hatching into a new handbird (adult size; the gem egg grows as it matures, making it worth more later on), and a 50% chance of shattering immediately when dropped by its parent.
These things are both nature and magic so breaking an egg is a sin against both, and shattering an egg triggers a "Summon Whatever Random Monster You Just Rolled" effect. The monster grows to full size over 3 rounds and only then will attack, but it has its full defenses, saves, and hd/hp at 'birth.'
Handbirds themselves are meek and rarely fight but unpaired handbirds will defend the roost of the mating pairs of its applause, scratching and throttling, especially with its bony lower hands. It can approximate punching someone by going into a power dive; with sufficient altitude, this can be like getting hit by a mace! In other regards they have similar stats compared with falcons.
They communicate over a distance of miles with rhythmic codes of snaps and claps. Their upper hands are wide and fleshy, while their lower hands are knobby and clawlike. They can be successfully raised as pets or familiars but they carry an association of doom and inconvenience. Their palms sweat a lot, which seems to be a form of waste excretion. It is not known what they eat, or how.