Some perspective on how large a number 3 billion is. It’s the low-end estimate of how many Passenger Pigeons we once had in the USA, and it’s the amount by which overall North American bird populations have been reduced since 1970.
You’ve heard the story before, and it’s sobering: Once perhaps the most abundant vertebrate on the planet, a combination of unremitting exploitation and habitat loss reduced the Passenger Pigeon (Ectopistes migratorius) from billions to none in a few short decades in the late 19th and early 20th centuries.
A recent analysis by Hung et al. 2014 used multiple sources of evidence to challenge the notion that Passenger Pigeons had always been that abundant. Their analysis does not, however, question the oft-cited estimate of somewhere between 3 and 5 billion Passenger Pigeons in North America at their population peak in the 19th Century. Even the low end of that estimate is difficult to fathom, so I decided to do a little back-of-the-napkin calculating to get a bit of perspective on what it would mean to have at least 3 billion birds of one species flying around North America.
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