Which bird species did ornithologist John Audubon observe in the early 1800s in a flock that he estimated was 16 kilometres wide and hundreds of kilometres long and consisted of perhaps a billion birds?

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John Audubon observed a flock of passenger pigeons in the early 1800s, which he estimated to be 16 kilometres wide and hundreds of kilometres long and consisted of perhaps a billion birds. The passenger pigeon was once the most abundant bird in North America but was hunted to extinction by the early 20th century.

Which Bird Species Did Ornithologist John Audubon Observe in the Early