Do miners (Manorinaspp.) affect bird assemblages in continuous savanna woodlands in north-eastern Australia?

Influence of the yellow-throated miner (Manorina flavigula) on bird communities and tree health in a fragmented landscape

Context Competition for space and resources within a fragmented landscape may change interspecific interactions within the remaining available habitat. These changes may inhibit the persistence of one species but facilitate the success of another. The yellow-throated miner (Manorina flavigula) is an example of a successful species, reportedly more common in the landscape as a result of fragmentation yet the consequences of its success are still relatively unknown. Aims To investigate whether the yellow-throated miner had negative impacts on bird community assemblages, particularly small insectivorous species, and whether its presence resulted in higher psyllid abundances and lower tree health, similar to impacts noted for other miner species. Methods We undertook this study near Walpeup in Victoria’s Mallee region, a highly fragmented, agriculture-dominated, semiarid landscape. Yellow-throated miner colonies and control sites free of miners were identified and surveyed for bird species present, psyllid abundance and measures of tree health. Conclusions The presence of the yellow-throated miner was associated with a significant reduction in bird species richness, lower abundance of small birds and a dissimilar community composition. Psyllid abundance was higher in miner colonies and tree health was significantly lower. Small insectivorous birds compete directly with miners for resources and, as such, are likely targeted by interspecific aggressive behaviour. The absence of small species from miner colonies most likely caused a trend in increased psyllid abundance and subsequently reduced tree health. Implications Our findings suggest that management of these miners is likely required to prevent further loss of biodiversity in this fragmented landscape. The loss of bird species and reduced tree health due to the influence of the yellow-throated miner presents one of the greatest threats to these communities nationally and a challenging conservation problem.

Disentangling how landscape spatial and temporal heterogeneity affects Savanna birds

In highly seasonal tropical environments, temporal changes in habitat and resources are a significant determinant of the spatial distribution of species. This study disentangles the effects of spatial and mid to long-term temporal heterogeneity in habitat on the diversity and abundance of savanna birds by testing four competing conceptual models of varying complexity. Focussing on sites in northeast Australia over a 20 year time period, we used ground cover and foliage projected cover surfaces derived from a time series of Landsat Thematic Mapper imagery, rainfall data and site-level vegetation surveys to derive measures of habitat structure at local (1-100 ha) and landscape (100-1000s ha) scales. We used generalised linear models and an information theoretic approach to test the independent effects of spatial and temporal influences on savanna bird diversity and the abundance of eight species with different life-history behaviours. Of four competing models defining influences on assemblages of savanna birds, the most parsimonious included temporal and spatial variability in vegetation cover and site-scale vegetation structure, suggesting savanna bird species respond to spatial and temporal habitat heterogeneity at both the broader landscape scale and at the fine-scale. The relative weight, strength and direction of the explanatory variables changed with each of the eight species, reflecting their different ecology and behavioural traits. This study demonstrates that variations in the spatial pattern of savanna vegetation over periods of 10 to 20 years at the local and landscape scale strongly affect bird diversity and abundance. Thus, it is essential to monitor and manage both spatial and temporal variability in avian habitat to achieve long-term biodiversity outcomes.