Big, flightless, insular, and dead: characterizing the extinct birds of the Quaternary

<p><b>Aim:</b> Birds have recently undergone a major extinction event which apparently, is ongoing. According to some estimates, humans have caused the extinction of up to 20% of the entire avian species diversity since the latter part of the Pleistocene, which is continuing at an unprecedented rate to this day. Few attempts, however, were made to determine how many extinctions are actually known, rather than projected to have occurred. We aimed to quantify the known avian extinctions, and assess the relevance of factors thought to have promoted their extinctions, i.e., large size, flightlessness, and insularity.</p> <p><b>Location:</b> Global</p> <p><b>Taxon:</b> Aves</p> <p><b>Methods:</b> We collected data on bird extinctions from the literature. We recorded the geographic range, flight ability, and body size of each species. If mass data were unavailable, we estimated it from linear measurements using machine learning tools. We modelled masses of extinct birds on those of extant ones and estimated the effects of taxonomy, body mass, insularity, and flight ability.</p> <p><b>Results</b> We have identified 469 species of birds that humans, directly or indirectly, drove to extinction. These extinctions have predominantly occurred on islands. Extinct birds were often flightless. We estimated the body mass of 291 extinct species and found that overall, the median mass of extinct species was seven times larger than that of extant ones. Extinctions mostly occurred in families of large-bodied birds, while lineages of small birds have fared better. Insular birds are overall larger than mainland birds, a trend that becomes even more evident when the extinct forms are analyzed. However, within lineages, sizes are only slightly larger on islands than on continents.</p> <p><b>Main conclusions</b> Our findings suggest that extinct bird species differed from extant birds by being larger, mostly restricted to islands, and often flightless. These factors made them especially vulnerable to human prosecution and to other anthropogenically-related declines. Our modern understanding of birds is skewed with respect to the nature of avian faunas that existed before the current wave of human-induced extinctions changed our world forever.</p>