The non-breeding period of pelagic seabirds, and particularly the moulting stage, is an important, but understudied part of their annual cycle as they are hardly accessible outside of the breeding period. Knowledge about the moulting ecology of seabirds is important to understand the challenges they face outside and within the breeding season. Here, we combined stable carbon (δ¹³C) and oxygen (δ¹⁸O) signatures of rectrices grown during the non-breeding period of two pairs of storm-petrel species breeding in the northern (European storm-petrel,Hydrobates pelagicus, ESP; Leach’s storm-petrel,Hydrobates leucorhous, LSP) and southern (black-bellied storm-petrel,Fregetta tropica, BBSP; Wilson’s storm-petrel,Oceanites oceanicus, WSP) hemispheres to determine differences in moulting ranges within and between species. To understand clustering patterns inδ¹³C andδ¹⁸O moulting signatures, we examined various variables: species, sexes, years, morphologies (feather growth rate, body mass, tarsus length, wing length) andδ¹⁵N. We found that different factors could explain the differences within and between the four species. We additionally employed a geographical distribution prediction model based on oceanicδ¹³C andδ¹⁸O isoscapes, combined with chlorophyll-aconcentrations and observational data to predict potential moulting areas of the sampled feather type. The northern species were predicted to moult in temperate and tropical Atlantic zones. BBSP was predicted to moult on the southern hemisphere north of the Southern Ocean, while WSP was predicted to moult further North, including in the Arctic and northern Pacific. While moulting distribution can only be estimated on large geographical scales usingδ¹³C andδ¹⁸O, validating predictive outcomes with food availability proxies and observational data may provide valuable insights into important moulting grounds. Establishing those, in turn, is important for conservation management of elusive pelagic seabirds.