The flight of the Passenger Pigeon: Phylogenetics and biogeographic history of an extinct species

Abstract

The human-caused extinction of the Passenger Pigeon (Ectopistes migratorius) is one of the best known and documented of any bird. This event was particularly alarming because the Passenger Pigeon went from being one of the most numerous avian species in the world to extinct in a period of decades, when the last individual died in captivity in a Cincinnati Zoo in 1914. While a great deal of information exists on the likely direct and indirect causes of its demise, as well as information on life-history, the phylogenetic relationships of this species have been subject to considerable speculation. Here we use DNA sequences obtained from museum specimens to resolve the phylogenetic position of this species with respect to other pigeons and doves (Columbiformes). We show that the Passenger Pigeon is not related to the New World mourning doves (Zenaida) as many authors have suggested, but is the sister taxon of all other New World pigeons (Patagioenas). Biogeographic analysis suggests the Passenger Pigeon lineage may have colonized North America from Asia, and subsequently dispersed into South America, leading to a more extensive radiation of New World pigeons.

Introduction

The Passenger Pigeon (Ectopistes migratorius) was once the most numerous species of bird in North America but, due to human over-exploitation combined with other factors, became extinct in a matter of decades. This dramatic decline is perhaps one of the best known and documented extinctions for any species, and has served as a poignant reminder of the impact humans can have on nature. Unlike many cases, where uncertainty exists regarding the exact timing of extinction, considerable documentation of the demise of the Passenger Pigeon exists (Schorger, 1955, Blockstein, 2002); the last bird died in captivity in a Cincinnati Zoo in 1914. Information on the natural history of the Passenger Pigeon has also been relatively well documented (Blockstein, 2002). However, the evolutionary relationships of the Passenger Pigeon have been the subject of speculation, with little or no rigorous phylogenetic testing.

The phylogenetic relationships of the Passenger Pigeon are generally unclear, and it has typically been placed in the monotypic genus Ectopistes. Most authors suggest that the Passenger Pigeon is closely related to the New World mourning doves (Zenaida), which include representatives in North and South America (Goodwin, 1983, Gibbs et al., 2001, Blockstein, 2002). Although the Passenger Pigeon shares a few superficially similar plumage patterns and a long tail with some members of Zenaida (Goodwin, 1983), it differs by its considerably larger size, sexual plumage dimorphism, and lack of a facial stripe. Because extant pigeons and doves (Columbiformes) in the New World have undergone three distinct radiations (Johnson and Clayton, 2000, Pereira et al., 2007), understanding the phylogenetic position of the Passenger Pigeon is important to more fully understand the origin of these radiations. Prior studies with limited taxon and gene sampling (Shapiro et al., 2002, Pereira et al., 2007) indicate that the Passenger Pigeon may not be closely related to Zenaida, as previously hypothesized. The goals of our study were to use additional DNA sequences obtained from museum specimens of the Passenger Pigeon and denser taxon sampling to identify its phylogenetic position within Columbiformes. We used this information to reconstruct biogeographic patterns in New World pigeons and doves.