2350 | wileyonlinelibrary.com/journal/jbi Journal of Biogeography. 2021;48:2350–2359. © 2021 John Wiley & Sons Ltd Received: 31 March 2021 | Revised: 8 August 2020 | Accepted: 5 May 2021 DOI: 10.1111/jbi.14206 RESEARCH ARTICLE Big, flightless, insular and dead: Characterising the extinct birds of the Quaternary Amir Fromm 1 | Shai Meiri 2 1 Department of Plant and Environmental Sciences, Weizmann Institute of Science, Rehovot, Israel 2 School of Zoology and the Steinhardt Museum of Natural History, Tel Aviv University, Tel Aviv, Israel Correspondence Amir Fromm, Department of Plant and Environmental Sciences, Weizmann Institute of Science, Rehovot, Israel. Email: amir.fromm@weizmann.ac.il Handling Editor: Jenny McGuire Abstract Aim: Birds have recently undergone a major extinction event which apparently is on- going. 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. Few at - tempts, however, were made to determine how many extinctions are actually known, rather than projected to have occurred. We aimed to quantify the known avian ex- tinctions and assess the relevance of factors thought to have promoted their extinc- tions, that is, large size, flightlessness and insularity. Location: Global. Taxon: Aves. Materials and Methods: 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 them from linear measurements using machine learning tools. We modelled masses of extinct birds on those of extant ones and esti- mated the effects of taxonomy, body mass, insularity and flight ability. Results: 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 spe- cies 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, whilst 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. Main conclusions: 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 anthropogeni- cally 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. KEYWORDS anthropogenic extinctions, avian biogeography, body-size evolution, flightlessness, Holocene extinctions, islands, Pleistocene extinctions