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.