Most Species Down to Fewer Than 50 Animals Recovered When Conservationists Stepped In, Study Finds
In the late 1970s, about 23 Lord Howe woodhens were left in the world, all on one small island off Australia's east coast, according to Monash University. A survey in December 2024 counted at least 1,638. A new study tested whether that bird is a lucky exception or part of a pattern among animals pushed this close to the edge.
Conservation biology has long viewed species reduced to critically small numbers with pessimism, as the study's own abstract notes. When only a few dozen animals remain, small population effects set in: relatives breed with relatives, genetic variety drains away, and one storm or disease outbreak can wipe out a large share of the group. Some conservationists have argued for triage, a way of ranking species that steers limited money away from cases judged too costly or too unlikely to succeed. Under that logic, a bird down to 23 individuals looks like a candidate to let go.
What 141 species showed
Donal Smith of Monash University led the team, with co-authors from Monash and the Zoological Society of London. They listed all 147 bird and mammal species known to have fallen below 50 individuals in the wild at any point since 1950. For 141 of them, enough time had passed to judge what happened next. The team recorded each species' history of conservation action, if any, and used a statistical model (Bayesian multi-level logistic regression) to test how that history related to later population size.
Fifty-one species received direct conservation action, and 61% of them recovered to at least 100 individuals. Among species that got no direct support, 37% went extinct and 2% climbed back to 100 or more. Direct action covered work such as controlling invasive predators, restoring habitat, captive breeding and translocation, which means moving animals to a new site to start or boost a population.
The best results came from pairing two kinds of work. One limits the outside forces driving a decline, such as predators or habitat loss. The other manages the population itself, for example by breeding animals in captivity and releasing them. Species that received both had the highest modelled chances of recovery. Smith said in the Monash release that population size "alone shouldn't determine whether we give up on a species."
How the woodhen came back
The Lord Howe woodhen is a flightless rail, a ground-dwelling bird in the same family as coots, found only on Lord Howe Island. Hunting and introduced predators drove its decline, according to a 2019 account of the recovery by Dean Portelli and Nicholas Carlile in the journal Ornithological Science. The rescue program began in the 1970s with the aim of removing feral pigs, cats and goats. In 1980, workers took three wild breeding pairs from Mount Gower, the island's highest peak, into captivity. Over four years, those founders and their offspring produced 76 chicks.
The bird faced one more hazard in 2019, when the island's managers spread poison bait to eradicate invasive rodents. To keep woodhens away from the bait, the Lord Howe Island Board held them in captive management and then released 208 birds, according to NSW Environment and Heritage. With rodents gone, the count reached at least 1,638 by December 2024. That total combines 1,535 adults and juveniles and 26 chicks from the 2024 survey with 77 birds counted on Mount Gower in 2022.
📍 Multiple Perspectives on the Story
The whole record, not the highlight reel
Famous comebacks have been told for decades, but the paper's abstract points out that success stories alone cannot show whether they are typical. Counting every species that fell below 50, including the ones that vanished, answers that. Co-author Rohan Clarke of Monash goes further in the release, calling it a mistake to abandon critically endangered species because their numbers look too low.
Setbacks along the way
The woodhen rescue did not run smoothly. Portelli and Carlile report that only 13% of the captive-bred birds released were seen again, and numbers rose at just one release site before falling there too. The wild birds left on Mount Gower did better: that subpopulation grew fivefold in the decade after captive breeding ended.
More birds, a narrow gene pool
In a 2020 Australian Museum post, Richard Major and Mark Eldridge reported that the woodhen's gene pool passed through a bottleneck of about 16 individuals. Comparing blood from a 2018 survey with DNA from 82 museum specimens collected in 1915, they found genetic diversity had fallen markedly. Most lowland birds appear to descend from a single pair. They recommend moving summit birds to the lowlands from time to time to spread the summit's extra variety.
Association, not proof
The authors call their work an observational study. It links action to recovery but cannot prove the action caused it. In our reading, species chosen for direct help may have had threats that were easier to fix, and the design cannot fully rule that out. By our arithmetic, about 20 of the 51 helped species still fell short of 100. Reptiles, amphibians, fish, insects and plants were not part of the analysis.
Budgets still run out
Triage supporters start from the budget. Conservation money is finite, and money spent on a near-hopeless case cannot go to a species with better odds. The study answers part of that argument: a low count by itself did not doom species that got help. Neither the abstract nor the release gives cost figures, so the work cannot say which rescues were the best use of money, or what to do where a threat cannot be removed.
What this does and does not mean
The record now covers every bird and mammal species known to have dropped below 50 wild animals since 1950, not only the famous rescues. Among those that got direct help, recovery to 100 was the more common outcome. Among those left without it, extinction came far more often than recovery. A count of 100 marks the study's line for recovery, not a guarantee of long-term safety, and whether recovered populations stay healthy over decades is still open. Six of the 147 species fell below 50 too recently for the study to judge, and their outcomes will add to the record.
Frequently Asked Questions
What did the 2026 study on small animal populations find?
The study, published November 4, 2026, in Proceedings of the Royal Society B, looked at all 147 bird and mammal species known to have fallen below 50 wild individuals since 1950 and assessed outcomes for 141. Of the 51 species that received direct conservation action, 61% recovered to at least 100 individuals. Among species without direct support, 37% went extinct and 2% recovered to 100 or more.
What counts as direct conservation action?
Hands-on work for a species or against the threats it faces, such as controlling invasive predators, restoring habitat, captive breeding and translocation (moving animals to a new site). Species that received both threat control and direct population management had the highest modelled chances of recovery.
How did the Lord Howe woodhen recover?
Managers set out in the 1970s to remove feral pigs, cats and goats from Lord Howe Island, then ran a four-year captive breeding program starting in 1980. A rodent eradication followed in 2019, with woodhens held in captive care during the baiting. The population grew from about 23 birds in the late 1970s to at least 1,638 in December 2024.
Does this study mean every endangered species can be saved?
No. It shows that a population count below 50 did not by itself doom species that got direct help, but it is observational, covers only birds and mammals, and gives no cost figures. About 4 in 10 helped species still did not reach 100 individuals, and threats that cannot be removed remain hard cases.