Pleistocene range dynamics and episodic rarity in an extinct bird

In an influential report in the field of conservation biology, Rabinowitz et al. (1) described seven ways in which species may show rarity, based on different combinations of range size, ecological amplitude, and local abundance; this paper has guided many avenues of thought in the field of conservation biology. To a conservation biologist in the 17th century, however, the passenger pigeon (Ectopistes migratorius) would not have qualified as “rare” under any of the seven categories; quite simply, the species had a broad range (eastern North America), was not particularly limited to any one set of conditions, and was massively locally abundant. Still, this species disappeared entirely by the early 20th century for reasons that have never been entirely clear. A report in PNAS by Hung et al. (2) sheds an initial glimmer of insight into this question. Hung et al. (2) took advantage of two new capabilities: robust historical demographic inferences based on information from across the genome, and estimates of geographic potential at the last glacial maximum (LGM) based on ecological niche models. Hung et al.’s demographic inferences were based on sequences of well over half of the genome (0.74–0.99 of a genome of likely about 1.30 gigabases) of three individuals, thus being based on variation across massive numbers of genes; they used coalescent sampling (3) to estimate genetically effective population size (Ne) and sequentially Markovian coalescent analyses (4) to assess changes in population size through time. These procedures yielded estimates that …