SummaryThe breeding community of petrels on the Chatham Islands has previously seemed curiously poor compared to that of analogous stations in the Indian Ocean or South Atlantic (14 species compared with 18 in the Tristan‐Gough group). Examination of subfossil deposits from the Chatham Islands probably dating from the early stages of human colonization which occurred within the last few hundred years reveals remains of at least 20 petrels, all of which except one may well have bred in the past, without including storm petrels, of which two species are still known to breed while others may also have bred in the past. The grand total of at least 21 breeding species, many apparently in vast numbers, would probably make the archipelago the most important breeding station for petrels in the world at the time of the first human colonization. It seems possible that in addition to the present breeding species the following may have bred: at least one endemic species of gadfly petrel, the Magenta PetrelPterodroma magentae, and local populations of at least two other gadfly petrels, two shearwaters of the genusProcellariaand two of the genusPuffinusand a sooty albatross of the genusPhoebetria. Small populations of these, and perhaps other undetected species as well, may still survive in inaccessible place