Short‐term response of a declining woodland bird assemblage to the removal of a despotic competitor

Abstract

Interspecific aggression by the noisy miner (Manorina melanocephala), a highly despotic species, is homogenizing woodland avifaunas across eastern Australia. Although a native species, the noisy miner's aggressive exclusion of small birds is a Key Threatening Process under national law. Large‐scale removal of noisy miners has been proposed as a management response to this threat following increases in miner presence due to anthropogenic land use practices. We tested this proposal by experimentally removing noisy miners from eucalypt woodland remnants (16–49 ha), assigned randomly as control (n = 12) or treatment (miner removal) sites (n = 12). Standardized bird surveys were conducted before and after removal, and generalized linear mixed models were used to investigate the effect of miner removal on bird assemblage metrics. Despite removing 3552 noisy miners in three sessions of systematic shooting, densities of noisy miners remained similarly high in treatment and control sites, even just 14 days after their removal. However, there was evidence of an increase in richness and abundance of small birds in treatment sites compared to controls—an effect we only expected to see if noisy miner densities were drastically reduced. We suggest that miner removal may have reduced the ability of the recolonizing miners to aggressively exclude small birds, even without substantially reducing miner densities, due to the breakdown of social structures that are central to the species' despotic behaviour. However, this effect on small birds is unlikely to persist in the long term. Synthesis and applications: Despite evidence from other studies that direct removal of noisy miners can result in rapid and sustained conservation benefit for bird communities at small scales, our findings cast doubt on the potential to scale‐up this management approach. The circumstances under which direct control of noisy miners can be achieved remain unresolved.

Patch‐scale culls of an overabundant bird defeated by immediate recolonization

“…However, a recent experimental cull with more replicates and in bigger sites than the work by Grey, also recorded rapid recolonization (Davitt et al. ). Where the recolonizing birds came from remains unclear.…”

“…, , Debus , Davitt et al. ) but at least six others have been undertaken in the same period, at different scales and with varying levels of success. The influence of local differences in vegetation configuration on the responses of metapopulations to culling makes broad inference from localized culls difficult.…”

“…It has been suggested, however, that removing whole colonies fosters recolonization whereas leaving parts of a colony intact maintains territoriality and therefore discourages recolonization (Davitt et al. ).…”

“…In a recent experimental cull, no such reduction in abundance was seen due to rapid recolonization (Davitt et al. ). The reasons for the variability in effects are unclear and, as Grey's studies used only three and four replicates, respectively, broader inference to other systems is limited.…”

“…In two of the four published studies on culls or translocations of Noisy Miners, average reductions in Noisy Miner abundance of between 35% and 71% in the 12-16 months following removal were achieved (Grey et al 1997(Grey et al , 1998. In a recent experimental cull, no such reduction in abundance was seen due to rapid recolonization (Davitt et al 2018). The reasons for the variability in effects are unclear and, as Grey's studies used only three and four replicates, respectively, broader inference to other systems is limited.…”