Barking Owl Ninox connivens has two recognised subspecies in Australia: N. c. connivens and N. c. peninsularis. N. c. connivens currently includes the isolated south-west Australian population, which is separated from eastern populations by the Nullarbor Plain and from N. c. peninsularis to the north. N. c. connivens in south-west Australia occurs from near Perth in the north, east to Northam and south-east to Katanning and Bremer Bay; it has been treated subspecifically as N. c. addenda Mathews, 1912, but this name is not currently in use. Given concern over the apparent rarity of the south-west Australian population, we sought to compile all known historical and contemporary records in order to assess its conservation status and ecology. We located the holotype of N. c. addenda Mathews, 1912, and found only ten sightings in the past 20 years that met our criteria for acceptance. No sound-recordings or photographs of wild birds are known.