Abstract
Biodiversity impacts caused by alien species can be severe, including those caused by alien birds. In order to protect native birds, we aimed to identify factors that influence their vulnerability to the impacts of alien birds. We first reviewed the literature to identify native bird species sustaining such impacts. We then assigned impact severity scores to each native bird species, depending on the severity of the impacts sustained, and performed two types of analyses. First, we used contingency table tests to examine the distribution of impacts across their severity, type and location, and across native bird orders. Second, we used mixed‐effects models to test factors hypothesised to influence the vulnerability of native birds to the impacts of alien birds.Ground‐nesting shorebirds and seabirds were more prone to impacts through predation, while cavity‐nesting woodpeckers and parrots were more prone to impacts through competition. Native bird species were more vulnerable when they occupied islands, warm regions, regions with climatic conditions similar to those in the native range of the invading alien species, and when they were physically smaller than the invading alien species. To a lesser extent, they were also vulnerable when they shared habitat preferences with the invading alien species.By considering the number and type of native bird species affected by alien birds, we demonstrate predation impacts to be more widespread than previously indicated, but also that damaging predation impacts may be underreported. We identify vulnerable orders of native birds, which may require conservation interventions; characteristics of native birds that increase their vulnerability, which may be used to inform risk assessments; and regions where native birds are most vulnerable, which may direct management interventions. The impacts sustained by native birds may be going unnoticed in many regions of the world: there is a clear need to identify and manage them.
Highlights
Invasive alien species are one of the five direct drivers of anthropogenic change in nature with the greatest global impact on biodiversity (IPBES 2019)
By considering the number and type of native bird species affected by alien birds, we demonstrate predation impacts to be more widespread than previously indicated, and that damaging predation impacts may be underreported
Under Environmental impact classification of alien taxa (EICAT), an alien species is allocated to one of five impact categories depending on its most severe documented impacts to a native species across its entire alien range: minimal concern (MC – meaning that whilst the alien species interacted with a native species, it caused no discernible impacts); minor (MN – the alien species caused impacts that affected the performance of individual native species); moderate (MO – the alien species caused declining populations of one or more native species); major (MR – the alien species caused native species extirpations that would be reversible if the nonnative species was removed); massive (MV – the alien species caused irreversible native species extinctions)
Summary
Invasive alien species are one of the five direct drivers of anthropogenic change in nature with the greatest global impact on biodiversity (IPBES 2019). They cause profound structural changes to food webs and ecosystem function (Gandhi and Herms 2010, Simberloff et al 2013), and are the most common threat associated with species extinctions worldwide since AD 1500 (Blackburn et al 2019). Progress has been made in identifying traits associated with alien bird species that influence the severity of their impacts (Shirley and Kark 2009, Evans et al 2014): these studies may help to identify damaging alien bird species and manage their impacts. We test three broad hypotheses in order to identify factors that influence the vulnerability of native birds to the impacts of alien birds
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