Dietary plasticity and the extinction of the passenger pigeon (Ectopistes migratorius)

The decline of passenger pigeons (Ectopistes migratorius) during the late nineteenth century continues to draw substantial public and scientific attention as perhaps the most (in-)famous extinction event in North America's recent history. While humans undeniably caused the extinction, the relative importance of indirect (habitat destruction) versus direct (overhunting) impacts has remained a mystery, in part, due to a lack of scientific evidence for critical aspects of the species’ dietary ecology. One key factor in explaining why passenger pigeons went extinct is that their highly specialized diet and foraging strategy, focusing on mast (tree nuts), were no longer feasible as the forested habitats that they depended on became depleted by deforestation. We used stable isotope (δ13C and δ15N, n = 94) and ancient DNA (n = 9) analyses of archaeological specimens to demonstrate that, during the later Holocene, passenger pigeons had a substantial degree of dietary plasticity (including some individuals specializing in consumption of agricultural crops) that could have allowed them to take advantage of other food opportunities when mast became scarce. Dietary variation is not linked with either biological age (juveniles versus adults) or haplogroup. These results suggest that habitat destruction was less important for the passenger pigeon's extinction than the impacts of hunting and trapping and highlight the tremendous potential of the archaeological record for exploring the factors that led to this species’ extinction.