Habitat requirements for two of Australia’s most threatened birds: King Island Brown Thornbill and King Island Scrubtit

Abstract

King Island Brown Thornbill Acanthiza pusilla magnirostris and King Island Scrubtit Acanthornis magna greeniana are amongst the top three bird taxa in Australia thought most likely to become extinct within the next 20 years. Despite being recognised as endangered for almost three decades, little is known of the distribution, population size and habitat characteristics of these endemic King Island subspecies and few on-ground recovery actions have been initiated. To establish baseline information to guide conservation decision making, in 2019–2022 we surveyed 1677 sites across the island for King Island Brown Thornbill and King Island Scrubtit and recorded a range of habitat variables at detection and non-detection sites to characterise the habitat requirements of both these taxa. King Island Brown Thornbill was found to occur in wet forests in a range of patch sizes. Mature eucalypts and a high tree canopy cover were found to be strong predictors of its presence, with
most detections in Brooker’s Gum Eucalyptus brookeriana wet forest and Blue Gum Eucalyptus globulus King Island forest. King Island Scrubtit was found to be restricted to five isolated locations. Swamp Paperbark Melaleuca ericifolia swamp forest supporting mature Swamp Paperbark and a high cover of coarse woody debris were found to be significant predictors of its presence. Protection of all remaining potential habitat for King Island Brown Thornbill and King Island Scrubtit may be required to prevent the extinction of these subspecies on King Island.