The gang wars that we often associate with a Hollywood movie franchise are happening in your very own backyard.
“I don’t feel I have to wipe everybody out, Tom. Just my enemies.”
Michael Corleone, The Godfather Part II
Across eastern Australia, there are places where native birds no longer dare to go. Fairy-wrens, finches and wood swallows once thrived in these woodlands, but have since been hounded from their homes by an unstoppable army of thugs. Unlike Michael Corleone and his goons, these perps are 60 grams of pure, feathery rage — noisy miners.
Endemic to Australia, noisy miners are among our largest honeyeaters. Although we often overlook them as just ‘another bird’ in our gardens and courtyards, noisy miners use their weight and dense colony numbers to mob, attack and even kill other bird species, usually in groups of five. Douglas Dow, a pioneer in the study of noisy miner behaviour, once observed two miners “persistently attack a full-sized, but immature, house sparrow, killing it after six minutes.”
This hyper-aggressive, highly despotic (and, frankly, psychotic) behaviour has a negative impact on populations of smaller, insectivorous birds, such as the threatened regent honeyeater and swift parrot. To stop this one-sided gang war, researchers have proposed culling noisy miners, a strategy rarely used on native species.
Historically, culls were often the secondary effect of hunting for trophies, fur and food. More recently, culls are undertaken when a native species’ presence is diminishing the population of a more endangered species. For example, between 1993 and 1996 on Cabbage Tree Island, off the coast of New South Wales, pied currawongs and Australian ravens were removed in a successful attempt to improve the island’s population of Gould’s petrel. But culls can be risky. Kill too few individuals and you have essentially wasted resources and all was for nothing. Kill too many and we threaten the population, as has happened with saltwater crocodiles, or, worse, we cause extinction, as with the Tasmanian tiger.
In the early 1990s, an experienced shooter used a .22 rifle to remove noisy miners from a remnant patch of vegetation in NSW. Stephen Debus, one of Australia’s foremost ornithologists on Australian raptors and native birds, analysed the long-term effects related to the cull. He found that community density of small woodland birds drastically improved after a miner cull. Most likely, this increase was not due to the cull alone, with Debus writing, “In conjunction with the cull, the land holder also planted up his property with native trees and shrubs, which would have helped bring other birds back”.
Despite this study, until now the long-term effects of culling noisy miners remained unexplored. Paul McDonald, head of the Avian Behavioural Ecology Laboratory at the University of New England, NSW, contributed to a recent experiment that compared species composition before, during and after a noisy miner cull. An expert shooter used a shotgun to shoot birds on sight, a strategy known as ‘happy families.’
“There was one professional shooter who took approximately two days to remove noisy miners per patch,” says McDonald. “It was quieter, as noisy miner calls are usually the most commonly heard calls in a patch of woodland that they occupy, so not hearing those calls makes a big difference”.
The cull showed that, immediately after noisy miner removal, the richness of other bird species improved. But this change is only temporary: Within two weeks of removing more than 3000 miners from randomly selected experimental sites, noisy miners had recolonised the area in even higher densities than before. It is, therefore, likely that culling of miners only provides a very short-term solution, essentially lasting for as long as it takes other colonies to realise that their neighbour is dead. Accordingly, to generate miner-free woodland, we would have to eliminate all colonies from the area rather than a few – a rather risky move.
Further, miners are highly successful in fragmented areas of woodland where there is little cover and strong human impacts. So even if we do completely remove miners and allow woodland species to move into these open areas, will other native species be able to persist in these highly unnatural conditions?
One possible solution is to make patches of woodland less desirable to miners by revegetation, possibly followed by a small cull. Wildlife corridors are becoming more common, with farmers attempting to revegetate their land to provide shade for livestock that also doubles as protection for smaller bird species. However, this solution might not be as simple as just planting trees. If these corridors only consist of eucalyptus trees, then they essentially act as forest edges — heaven to a miner bird, but not for other native species.
To see richness and variation in bird species, we must create variation in the vegetation that we plant. A 2006 study found that native revegetation projects should include a combination of eucalypts and acacias, and a shrubby understorey that will act as both food and shelter for these smaller species. Interestingly, without an initial cull of noisy miners, sites that were forested with less than 85% eucalypts, at least 20% understorey, and some acacia species, did not have miners present. This suggests that where we plant might not be of as much importance as what we plant.
This approach provides a long-term alternative to noisy miner culls that might help us all sleep a little easier at night. After all, maybe miners are not the villains here. Yes, they exclude small birds from fragmented patches of woodland, but they also provide food and protection to many other species. Additionally, can we ethically punish a native species for not only coping, but succeeding in the highly modified environments that we have created? Rather than reprimanding miners, perhaps we should look at trying to bring back the natural beauty of our landscapes. If we bring back the greenery beneath the eucalypts, we may once again hear the chattering of different native woodland birds in our gardens.
Edited by Andrew Katsis and Ellen Rykers