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Thirty breeding colonies of three petrel species were found on 23 of 41 islands and one of three headlands surveyed between Milford Sound/Piopiotahi and Dagg Sound/Te Rā in Fiordland National Park, New Zealand, in November 2020. Sooty shearwater (Ardenna grisea) was the most widespread and abundant species, with an estimated 7,300 burrows on 20 islands and one mainland site. Broad-billed prions (Pachyptila vittata) were found breeding on five islands (600 burrows estimated), including an islet in Poison Bay, 70 km north-east of their previous northernmost Fiordland breeding location. We record the first evidence of mottled petrels (Pterodroma inexpectata) breeding in Doubtful Sound/Patea (on Seymour Island), which is now their northernmost breeding location. When combined with data from surveys in southern Fiordland between 2016 and 2021, more than 66,000 pairs of petrels are estimated to be present in 168 colonies in Fiordland. This total comprises 42,100–52,400 sooty shearwater pairs, 11,700–14,500 broad-billed prion pairs, 5,090–6,300 mottled petrel pairs, and at least 1,000 common diving petrel (Pelecanoides urinatrix) burrows. This is the first near-complete estimate of petrel population sizes for the Fiordland region.