Estimating population size of the Black-eared Miner, with an assessment of landscape-scale habitat requirements

Abstract

The decline of the Black-eared Miner Manorina melanotis has been caused primarily by habitat degradation and vegetation clearance. To better direct conservation actions for this species there was a need to assess habitat requirements on a regional-scale and to estimate the population size using quantitative methods. We used vegetation mapping and the current distribution of the Black-eared Miner to determine regional-scale habitat requirements. These findings were combined with the results of distance sampling to provide population estimates. The species is restricted to large tracts of intact mallee in the Murray Mallee of southeastern Australia that have not been burnt for at least 45 years. The density of Black-eared Miners is highest in areas that are dominated by mallee-Triodia associations and have not been intensively grazed. The Bookmark Biosphere Reserve supports an estimated 501 (270-927, 95% CI) colonies, containing 3 758 (2 026-6 954) phenotypically pure Black-eared Miners, 2 255 (1 215-4 170) hybrids and small numbers of Yellow-throated Miners Manorina flavigula. However, the effective population size is considerably smaller (390 Black-eared Miners (210-726) and 234 hybrids (126-433)). due to a skewed adult sex ratio (1 female: 1.81 males) and complex social organization. A smaller population also persists in the Murray Sunset National Park containing 53 (32-85) Black-eared Miner/hybrid colonies. Both populations face a high risk of extinction from large-scale wildfire. The endangered status of the species under IUCN criteria remains warranted.