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

Aim: 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. Location:
Global Taxon: Aves 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 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. 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 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. 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 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.