. Bulletin of the British Ornithologists' Club. S. H. M. Butchart et al. 17 Bull. 2006 126A invasive species were a major contributory factor to 51% of recent avian extinctions. Blackburn et al. (2004) and Clavero & Garcia-Berthou (2005) also provided strong evidence of the importance of invasive species in driving avian extinctions. It is important to note that many species are impacted by combinations of threats: of extinct species have multiple causes of extinction recorded, and this figure is likely to be an underestimate owing to lack of information on historical extincti
. Bulletin of the British Ornithologists' Club. S. H. M. Butchart et al. 17 Bull. 2006 126A invasive species were a major contributory factor to 51% of recent avian extinctions. Blackburn et al. (2004) and Clavero & Garcia-Berthou (2005) also provided strong evidence of the importance of invasive species in driving avian extinctions. It is important to note that many species are impacted by combinations of threats: of extinct species have multiple causes of extinction recorded, and this figure is likely to be an underestimate owing to lack of information on historical extinctions. There are differences in the causes of extinctions of island versus continental species, with habitat loss and exploitation appearing to be more important causes of extinctions on continents than islands, although this result was marginally non- significant (habitat loss: vs. of species; exploitation: vs. of species; invasive species: vs. of species; x2= , P=; Fig. 6). The apparent reduced importance of exploitation as an extinction driver on islands may be partly explained by the fact that passerines (which, being smaller, are less often targets for hunting) form a substantially lower proportion of island extinctions compared to continental extinctions (see above). It may also be a consequence of an extinction filter effect (Balmford 1996): non-passerine island species susceptible to exploitation through their size and naivete may have already been driven extinct prior to 1500. It is interesting to compare the threats to Extinct and Possibly Extinct species with those to extant threatened species (Fig. 7). Whilst habitat loss is the most important factor in both cases (impacting of extinct species and of threatened species), invasive species and exploitation were much more important as. â Continent â¡ Island T> O £ E Cause of extinction Figure 6. Causes of recent avian extinctions on continents («=16 spe
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