The passenger pigeon is the poster species for human-caused extinction. From a population of between three and five billion in the 1800s, the pigeon’s numbers plummeted to zero in 1914, an extinction generally blamed on humans shooting the birds for sport.
But as it turns out, humans were only part of the story. DNA sequencing of preserved birds has revealed that their numbers were pushed downward by natural forces, which left them more vulnerable to extinction.
Scientists found that the bird’s “genetically effective” population size – basically, its levels of genetic variation – was much lower than expected. Not only that, but the abundance of acorns, one of the pigeons’ main food sources, fluctuated greatly over the previous 21,000 years.
Read the full, original story: Humans Aren’t Solely to Blame for Passenger Pigeon Extinction