Combining survey and remotely sensed environmental data to estimate the habitat associations, abundance and distribution of breeding thin-billed prions Pachyptila belcheri and Wilson’s storm-petrels Oceanites oceanicus on a South Atlantic tussac island

Abstract Small petrels are the most abundant seabirds in Southern Ocean. However, because they breed burrows on remote and often densely vegetated islands, their colony sizes conservation status remain poorly known. To estimate abundance of these species Bird Island Falkland archipelago, we systematically surveyed breeding burrow density occupancy across this near-pristine tussac ( Poa flabellata )-covered island. By modelling as functions topography Sentinel 2 satellite-derived Normalised Difference Vegetation Index data, inferred habitat associations predicted commonest species—Thin-billed Prions Pachyptila belcheri ) Wilson’s Storm-petrels Oceanites oceanicus ). We that there 631,000 Thin-billed Prion island (95% CI 496,000–904,000 burrows). Assuming lies between 12 97%, equates to around 76,000–612,000 pairs, making second or third largest P. world, holding approximately 3–27% species’ population. 8200–9800 5,200–18,300 pairs) pairs also Notably, latter burrowed predominantly under within pedestals, whereas usually assumed rock cavities. declining Kerguelen but population trends Falklands unknown. Given wide confidence intervals our own other estimates for cryptic species, recommend populations should be monitored regularly, at multiple sites.