Crows, ravens and their relatives are famed for being very intelligent birds. Several species, including the Caledonian crow and the rook, are known to use tools. For example some drop the toughest nuts on to busy roads and wait for the traffic to crush them. There are over 120 species in this family including jays, magpies, choughs and the common raven (the largest species) distributed worldwide except on the polar caps. Most members form very strong pair bonds that, in some species, last a lifetime.