pigeons are domesticated rock doves. rock doves nest in small caves, so the only nest building they need to do is a few sticks to prevent eggs from rolling out of the caves.
seems like in the apollo era crew carried a few in their PPK (personal preference kit), and in the later shuttle era they regularly carried 500-1000 pins per mission.
> It required an input key that was unique to our dongle series & our own code that was whatever we wanted. The reply was a hash of both values.
> The last version we used was USB. They retired the parallel style long ago.