Science for Saving Species Research findings factsheet Project 4.2 Assessing the impacts of invasive species: Hollow-nesting birds in Tasmania In brief Background Predicting the impacts of invasive Invasive alien birds are found explore the known and theoretical species is difficult at large spatial across many areas of Australia. interaction network between the scales. This is because the interactions Many of these introduced birds cavity breeding birds in Tasmania, between invasive species and native use cavities, an important breeding and to identify which native species species vary across different species, resource for cavity nesting species. are likely impacted by the addition between different locations, over In Tasmania alone there are 27 of non-native species. time and in relation to other pressures species of hollow-nesting birds, We discovered that, overall, such as habitat loss, extensive fires, including three threatened species native hollow-nesting species climatic events and drought. and seven invasive hollow-nesting are likely facing increased levels bird species. The logging of big old Given that conservation and of competition for nesting sites trees with cavities and the addition management work is almost always as a result of non-native species of invasive species has likely led conducted under limited budgets and introductions. Such competition to increased competition over time, being able to quantify where is likely to decrease breeding the limited resource. However, and when invasive species are having opportunities for native species, the impact of most of these a significant impact on local species including some of Tasmania’s invasive species has not been is vital for effectively managing and threatened and endemic species. studied. Therefore, we set out to prioritising actions to address threats posed by invasive species. Orange-bellied swift parrot in nest box. In Australia, around 15% of all birds Image: ANU require tree hollows for nesting and breeding, which is a high proportion compared to bird communities in other parts of the world. While we know from previous research that the impact of invasive cavity-nesting species on the native species that require similar nest sites, the exact impact of most individual invasive hollow-nesting species remains unknown. A better understanding of which species share nest-site requirements could help inform where invasive species impacts are occurring, especially where behavioural studies on invasive–native species interactions have not been done. Tasmania’s non-native birds Tasmania is home to 27 hollow- laughing kookaburra, galah and competing for nest boxes with nesting bird species including rainbow lorikeet. The two non- orange-bellied parrots and swift seven invasive species of hollow- Australian invasive species are the parrots (see Figure 2). However, with nesting birds (Figure 1). Many of common myna and the common the other invasive birds covering the introduced species come from starling. Of all of the invasive species, much of the island, new approaches the Australian mainland, including only the common starling’s impact are needed to predict where they the little corella, long-billed corella, has been recorded, specifically might be impacting native birds. LEFT: Figure 1. There are seven introduced Australian Non-Australian Tasmania hollow-nesting species in Tasmania, making introduced species introduced species up 26% of the entire hollow-nesting bird Landuse community. Competition for nesting space is the primary impact of invasive hollow- nesting birds in Tasmania. Predicting and assessing the impacts on specific threatened species (forty-spotted pardalote, orange- bellied parrot and swift parrot) as well as its endemic species (e.g., the green rosella) is critical for prioritising mitigation actions. What we did We reviewed published information on inter-species interactions, such as documented competition for nesting hollows or habitat. We compiled data on the traits of hollowing nesting birds in Tasmania, such as: • bird body size • nesting months • hollow preferences (cavity entrance size, cavity type) • if they are obligate tree-hollow breeders or will also use other nest types. We modelled the breeding niche (nesting preferences) of all 27 hollow- nesting bird species in Tasmania and assessed the level of niche overlap between every possible combination Figure 2 of native and invasive species. We identified species combinations with: a) documented inter-species Research aims competition; and/or b) predicted This study aimed to examine the theoretical breeding competition among high levels of breeding niche overlap. native and introduced cavity nesting birds in Tasmania and review which In combination this allowed us to invasive and native species are likely to interact most frequently around identify which species are likely to nesting sites. Our overarching aim was to identify where and when the be competing for nesting sites and impacts of invasive species impacts are most likely to take place – that is, where, and the predicted level of where management action is most needed. this interaction. Key findings Non-native species share nest-site from invasive species, but it faces Only around a tenth of the native preferences and/or compete competition and predicted breeding species (11.5%) we predict are facing with 13 native species (65% of the niche overlap with the striated increased competition have been native cavity-nesting community pardalote and the tree martin. studied in the field, highlighting in Tasmania), including the In turn, the tree martin is impacted the lack of information available threatened swift parrot, orange- by the native owlet-nightjar and to conservation managers. bellied parrot and masked owl. invasive laughing kookaburra, Our models are intended to improve This suggests that most native so there may be indirect effects. how we can predict the impact species are likely facing higher of poorly studied invasive birds There had been little previous levels of competition and therefore across Australia in particular, field research on how competition potentially reduced opportunities helping us understand where influences the nest-site choice for breeding as a result of non- and when significant impacts and habitat use of many common native species introductions. on native hollow-dependent species, including several species are likely to take place. The Critically Endangered swift endemic birds. parrot is likely to face the most competition from invasive species; there is a high level of predicted Tasmanian species facing high levels of Invasive species breeding niche overlap between competitive impact the common myna and common starling. While the common starling Swift parrot*, green rosella, Tasmanian boobook, is widespread across Tasmania, Common myna musk lorikeet, chestnut teal, Australian owlet-nightjar, the common myna has not yet eastern rosella established breeding populations so efforts to prevent its Swift parrot*, eastern rosella, orange-bellied parrot*, establishment are warranted. Australian owlet-nightjar, blue-winged parrot, green Common starling rosella, masked owl, chestnut teal, Australian The Critically Endangered orange- wood duck, tree marti bellied parrot likely faces substantial competition for breeding hollows Yellow-tailed black-cockatoo, masked owl, nankeen with several native species including Galah kestrel, Tasmanian boobook swift parrots, blue-winged parrots and Australian owlet nightjars and Laughing Masked owl, nankeen kestrel, sulphur-crested non-native species such as the kookaburra cockatoo, yellow-tailed black-cockatoo, tree martin common starling. The impact of this competition is exacerbated Little corella Sulphur-crested cockatoo when suitable hollows are limited, and designing suitable nest Long-billed Sulphur-crested cockatoo, green rosella, boxes for these species that also corella Australian shelduck exclude competitors could be a useful management approach to Rainbow lorikeet Blue-winged parrot, eastern rosella increasing the nesting opportunities. The Endangered forty-spotted Table 1. Invasive hollow-nesting bird species in Tasmania and the native hollow-nesting species with which there are high levels of competition. Impact is assessed based on competitive pardalote does not face direct impacts documented in the literature and predicted level of breeding niche overlap (bold). niche overlap and competition * = threatened species Implications and recommendations By developing models of species The high impact of the invasive agricultural and urban land use, competition, we can help identify common starling, including on and given that many non-native areas where the potential impact threatened species, calls for further species first establish in altered of invasive species is likely to be research to determine exactly habitats. In order to conserve the highest. Given the addition of how significant the competition native hollow-nesting species, seven new species to the local from this bird is in the field. As native forest, especially old communities and consequent both these invasive birds do well growth, and older/dead trees increase in complex competition, in modified habitats, management with hollows in rural landscapes finding novel methods of predicting efforts towards them will likely be must be protected. In select areas where and when the impacts beneficial for native species nesting with high abundance of feral cavity- will occur, and which species