Rapid southward range expansion of the Fairy Gerygone – a consequence of climate change?

Abstract

Until the 1920s, the Australian range of the Fairy Gerygone Gerygone palpebrosa was thought to extend south from Cape York to Cardwell (18.3°S), Queensland. However, by 1981 the species was known to occur as far south as Tin Can Bay (25.9°S), and, by 1990, the Sunshine Coast (26.6°S). Sightings of individuals in the Brisbane region (27.5°S), 170 km south of Tin Can Bay, during 2011 and 2012 prompted a review of the southern range limits of the species, and consideration of causes for its southward range expansion. I collated records south of the 26°S parallel using three databases (eBird, WildNet and Atlas of Living Australia), then selected 30 sites that represented their spatial and temporal extent, noting their elevation, distance to the nearest coastline or watercourse, and vegetation according to the Regional Ecosystem classification. Sightings in the Brisbane region have been mostly along rivers or creeks emptying into Moreton Bay, suggesting that dispersal occurs southward along the coast, then inland via watercourses. Rather than being gradual, range expansion in this species has been characterised by ‘leaps’ of 45–59 km at intervals of 6–16 years. Since the early 1970s, at least five other tropical bird species have expanded their range southwards to Coastal Central Queensland. The most likely explanation for such range expansions is birds exploiting ‘new’ areas with suitable thermal regimes that have become available due to global warming. In the Fairy Gerygone, this process may be facilitated by (1) this species’ partiality for forest edge and riparian habitats, and (2) reduced competition with other gerygone species due to differences in preferred habitats and bill morphology.