A long tern view: distribution of small terns (Sternula) in Western Australia and implications for their conservation

Abstract

Recent observations confirm the Indo-Pacific Little Tern Sternula albifrons sinensis has been extending its breeding range in Western Australia in recent years, following a pattern documented in other tern and noddy species on the western coast of Australia. Nesting Indo-Pacific Little Terns have been recorded annually as far south as North West Cape since 2016. A similar southward shift in breeding range may have occurred during the last interglacial period and it is hypothesised that Little Terns isolated at the Houtman Abrolhos Islands during the following glacial period gave rise to the Australian Fairy Tern Sternula nereis nereis. The Australian Fairy Tern subsequently colonised the continental shelf from Dampier, Western Australia to the south-eastern states and then New Zealand as sea levels rose again during the Holocene. The two former sibling species are now sympatric between Dampier and North West Cape and interbreeding and hybridisation have the potential to occur in that area. Most jurisdictions require populations to be defined at the species or subspecies level in order to be listed and managed as threatened. However, relying on such taxonomic criteria has the potential to obscure the management of threats faced by each inter-breeding population unit. Approaches that identify and protect the sub-structure of superspecies and meta-populations might be more effective in the longer term.