Abstract
Invasive alien species are a major cause of biodiversity loss globally, but especially on islands where high species richness and levels of endemism accentuate their impacts. The Red vented bulbul (Pycnonotus cafer), a tropical passerine bird that has been introduced widely across locations of high conservation value, is considered an extreme pest. It is currently expanding its range in New Caledonia, one of the world’s biodiversity hotspots. Decisive recommendations on management strategies are required urgently to inform local managers and policy makers, but they should be based on quantitative local evidence, not just on expert opinion. The Red-vented bulbul is widely blamed for its impacts on biodiversity, especially through competition. We used data from 2,472 point counts to explore the abundance relationships between the Red-vented bulbul and 14 other species of bird. Our results revealed a negative relationship between the occurrence of the bulbul and the mean abundance of nine species, all native (or endemic, n = 3) to the New Caledonia archipelago. In contrast, the abundance of other introduced species such as Acridotheres tristis (Common myna), Passer domesticus (House sparrow) and Spilopelia chinensis (Spotted dove) were not affected by the Red-vented bulbul. Moreover, temporal trends in the abundance of impacted species suggest that the Red-vented bulbul may cause niche contractions rather than mortality for native species in man-modified habitats. Monitoring and control of the Red-vented bulbul is recommended to prevent on-going impacts on native bird communities throughout New Caledonia, and its impact on native bird communities elsewhere should be quantified.
Highlights
Exotic species play a major role in the decline of native species globally, but especially on islands with high species richness, high levels of endemism, and naivety towards novel predators and competitors [1,2,3,4,5]
Based on all point counts available from this area (N = 1139), we found that the Red-vented bulbul (RVB) mean abundance did not vary significantly across years (S3 Table)
The mean number of RVBs was significantly higher in man-modified habitats (1.19 ± 0.09; n = 216) and lower in forest habitats (0.14 ± 0.04; Invasive Red-vented bulbul outcompetes native tropical birds n = 444)
Summary
Exotic species play a major role in the decline of native species globally, but especially on islands with high species richness, high levels of endemism, and naivety towards novel predators and competitors [1,2,3,4,5]. Invasive Red-vented bulbul outcompetes native tropical birds species is a matter of debate [6,7,8,9]. Recent models suggest that 16% of biodiversity hotspots are highly vulnerable to invasive species [13,14,15], because of various pressures on native biodiversity through predation, competition, disease transmission, hybridization and ecosystem perturbation [16,17,18]. Most data on animal invasions have been derived from studies on established and stable alien populations, often from a macro-ecological perspective [19], and interest from researchers and managers has been biased towards some invasive taxa such as mammals [20]. More data are needed on earlystage dispersal processes and impacts to help predict, prevent, and manage harmful impacts [21,22]
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