Why the passenger pigeon matters to conservation science

Understanding why the passenger pigeon matters ecologically requires understanding what it actually was. Population estimates before European colonisation run to three to five billion individuals, roughly a quarter of all birds on the continent. Flocks took days to pass overhead. When they roosted, branches broke under their collective weight. John James Audubon, writing in the 1830s, described the sound of an approaching flock as a tornado. Their droppings fell like sleet.

Their movement through eastern North American forests was structurally important in ways that took decades after their extinction to fully appreciate. Passenger pigeons consumed mast — acorns, beechnuts, chestnuts — in such quantities that they regulated which tree species dominated the canopy. Their roosting disturbed undergrowth and created the kind of patchwork forest that dozens of other species had adapted to over millennia. When they disappeared, oak forests spread. Species that depended on the disturbance cycle the pigeons created found themselves without it. The forest that European settlers described as primordial was, in significant part, a product of the passenger pigeon.

Whether reintroducing a genomically reconstructed version would restore any of that is genuinely unknown. It would need to be released in numbers large enough to actually function as a flock species; a single breeding pair accomplishes nothing ecologically. The social behaviour that made passenger pigeons what they were may not transfer automatically through genome editing, and pigeons are not a blank slate onto which traits can simply be written. These are real scientific uncertainties, acknowledged openly by Revive & Restore. The passenger pigeon project continues anyway, because leaving the question permanently unanswered forecloses options that may matter more as habitat loss accelerates.

The ferret project at Revive & Restore offers the clearest evidence of what genomic conservation can achieve in practice. Elizabeth Ann, the first endangered US species to be successfully cloned, was born in 2020 from cells banked in 1988. Willa, the ferret whose tissue was preserved at the San Diego Frozen Zoo, died in Wyoming with no living descendants; her genetic material sat in cryogenic storage for 32 years until the cloning technology caught up. Her story is the most direct line between de-extinction infrastructure and conservation outcomes that are already measurable.

The woolly mammoth and the permafrost problem

The commercial energy in de-extinction is currently concentrated on the woolly mammoth, which has attracted the most investment and the most coverage. The project's scientific foundations were laid at Harvard Medical School, where Prof. George Church's lab at the Wyss Institute for Biologically Inspired Engineering first inserted mammoth cold-tolerance genes into Asian elephant cell lines using CRISPR in 2015. Colossal Biosciences, co-founded by Prof. Church in 2021, has since raised $448 million to take the research from lab to living animal. For the mammoth, that means editing the thick subcutaneous fat, the shaggy outer coat, and the adapted haemoglobin that releases oxygen efficiently at low temperatures into a living Asian elephant genome. What emerges will carry mammoth traits in an elephant body, capable of doing the same ecological work.

That ecological argument is central to how scientists justify the mammoth project beyond spectacle. Woolly mammoths spent tens of thousands of years as ecosystem engineers in Siberian grasslands, compacting snow in winter to allow cold to penetrate the permafrost and keep it frozen, and knocking down trees to maintain open grassland rather than the scrub forest that replaced them after their extinction. Siberian permafrost holds an estimated 1.5 trillion tonnes of frozen organic carbon. As it thaws, it releases methane. Bringing back something that functions like a mammoth, at scale, could slow that process — though the scale of reintroduction required to have measurable effect is enormous, and most climate scientists treat it as a supplementary measure at best. It is, however, a testable ecological hypothesis, and that separates it from wishful thinking.

What the commercial investment has done, beyond funding the research itself, is accelerate the underlying genomic tools in ways that benefit conservation biology well beyond de-extinction. CRISPR editing at the precision and throughput Colossal Biosciences requires has driven advances that researchers working on coral thermal tolerance and ferret disease resistance are now using. The technologies are shared. Whether de-extinction diverts resources from protecting species still alive — a concern raised regularly by traditional conservationists — is complicated by the fact that the two fields are drawing on the same toolbox and, increasingly, the same institutions.

Ryan Phelan, whose organisation is running the passenger pigeon project alongside its genetic rescue work on living species, puts the tension directly: de-extinction and conventional conservation are not in competition. The field of genetic rescue, which uses genomic tools to pull species back from the brink before they go the way of Martha, is where the most immediate results are appearing, and it is examined in detail in the next article in this series. The de-extinction projects are generating the science that makes genetic rescue more precise, more targeted, and more effective at identifying which interventions will actually work.

The next decade will produce the clearest results this field has ever seen: either living animals from extinct lineages, or a definitive understanding of why certain reconstruction approaches fail and what would need to change. Several leading genomics researchers now expect the first viable cold-adapted elephant calf within ten years. Whether that animal goes to Siberia, to a zoo, or becomes the foundation of a breeding programme depends on scientific, political, and financial decisions that have not yet been made. The science is running ahead of the governance, which is where most genuinely new fields find themselves.