Most abundant bird ever

It is impossible to provide an exact count of specimens of the passenger pigeon (Ectopistes migratorius) of North America, but even conservative estimates of the total population at its peak indicate that during the early 19th century there were between 5 and 10 billion birds. Their flocks darkened the skies when in flight, took up to three days to pass overhead and a single flock could contain more than 2 billion birds. Not surprisingly, their huge numbers also made them popular targets for hunters, which would ultimately lead to their demise by the early 20th century.

On 1 September 1914, the very last known passenger pigeon, an adult female called Martha, died in Cincinnati Zoo. The most abundant species of bird that our world has ever known was now extinct.