The Marlborough Sounds Important Bird Areas are four distinct sites comprising several small, rocky islets contained within an area with a maximum linear extent of 40 km, in New Zealand. They lie close to Cook Strait in the outer Marlborough Sounds at the northern end of the South Island. The sites are Duffers Reef, Sentinel Rock, White Rocks and the Trio Islands. They have been identified as Important Bird Areas (IBAs) by BirdLife International because they hold the only known colonies, and encompass the entire breeding range, of the vulnerable rough-faced shag (also known as the New Zealand king shag).