In March 1989 at least 172 Common (Sterna hirundo) and Sandwich (S. sandvicensis) Terns, predominantly the former, were killed by colliding with an electrical cable in Cape Town docks. Mortalities probably occurred early in the morning as birds left a nearby roost for their feeding grounds. The cable with which the birds collided was subsequently lowered by one metre and P.V.C. streamers were suspended from it to improve its visibility. Only two mortalities were recorded in 1990.