Projecting the current and potential future distribution of New Zealand’s invasive sturnids

Invasive species threaten native ecosystems, the economy and human health. Improved understanding of an invasive species’ ecological niche, and whether it has differentiated in the invasive compared to the native range, will enable better prediction of areas at risk of future invasions. Here, we characterise the ecological niche of the common myna ( Acridotheres tristis ) and common starling ( Sturnus vulgaris ), in their native range and in Aotearoa New Zealand, where they were introduced over 140 years ago. Common myna and common starling are two of the most invasive bird species in the world and are agricultural pests, competitors to native fauna and may act as disease vectors. Using biologically justified environmental variables and occurrence data, we construct ecological niche models (ENMs) using five algorithms. Based on the ENM algorithm with highest transferability, we identify key environmental variables to compare the niches of the two species in New Zealand and the native range, and between the two species in New Zealand. For both species, we find no evidence of niche divergence between New Zealand and their native range despite their long invasion history. However, we do find evidence for niche differences between the two species in New Zealand. Our future suitable habitat predictions suggest little range expansion of the already-widespread starlings in New Zealand, but large areas at risk of future myna invasion in New Zealand’s South Island. Our results support ongoing management of myna populations, especially in the South Island where the Cook strait may already provide some barrier to dispersal.