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Population Nosedive

The sad saga of the poor passenger pigeon has long served as an ultimate example of the awesome destructive power humans can unleash on the world.

Once one of the most populous animals in the world, with an estimated population of between three billion and five billion in the US alone, the bird's numbers plummeted from billions to zero in less than a century.

It was fitting that when the last lonely representative of her species, Martha, died, she was in human captivity, as it was people hunting the pigeons and carving up their habitats that did them in, wasn't it?

Maybe the real story is not that simple, says the passenger pigeon's genome.

According to a new genetic analysis of three old samples found in museums, intentionally released a century since Martha went talons up at the Cincinnati Zoo in the Proceedings of the National Academy of Sciences, there likely was a natural component that gave humans a helping hand in wiping out the passenger pigeon. Although the bird was indeed wildly populous in the 1800s, right before its population nosedived, it appears that it was not always so numerous, the researchers from the National Taiwan Normal University say.

Genome sequencing suggests that the pigeon's population may have fluctuated quite dramatically, and that natural ecological conditions may have interacted with human exploitation to wipe out the bird. Over the past million years, the authors calculate, the passenger pigeon population was just 1/10,000th of its number in the 1800s, and there probably was great variation on a year-to-year basis over the past 21,000 years.

"We think if this [cycle] is what really happened, it would explain why the passenger pigeon went extinct so rapidly," lead author Chih-Ming Hung tells the Los Angeles Times.

It makes sense that pigeon populations would swing wildly, GrrlScientist notes in her blog at the Guardian, as their primary food source was acorns, chestnuts, and other seeds, which also vary greatly in annual abundance. Also, because the birds tended to roost in great numbers, they were easy targets for infectious diseases. It is likely that the passenger pigeon's numbers were on a downswing to begin with, the authors suggest, and human intervention accelerated that precipitous drop and then finished them off.

This knowledge may alleviate a bit of the guilt people might feel about wiping the passenger pigeon off the plant, but that is no reason not to bring them back from extinction.