When only 20 or 30 animals of the same species remain in the wild, extinction often seems inevitable. Individuals struggle to find mates, and their offspring are more likely to share the same ancestors. Yet a new study shows that these populations are not necessarily doomed.
Researchers from Monash University in Australia and the Zoological Society of London examined the fate of threatened birds and mammals. What they had in common was that each species had fallen below the threshold of 50 individuals living in the wild since 1950. Of the 147 species identified, 141 had enough data to assess their development.
A Lord Howe woodhen (Gallirallus sylvestris)
Image Wikimedia
The results are striking. Among the 51 species that benefited from direct actions to increase their numbers, 61% recovered to at least 100 individuals. By contrast, among those that received no direct help, only 2% reached that level. In the latter group, 37% of the species disappeared.
What does direct help mean? It may involve raising animals in specialized centers before releasing them. Teams can also move certain individuals to a suitable area to reinforce a population that is too small. These interventions require time, resources and a good understanding of the animals concerned.
But producing more offspring is not enough if the causes of the decline remain. A predator introduced by humans may continue to kill newcomers. Likewise, a destroyed habitat can no longer sustainably support a growing population. The study's best results concerned species for which teams combined several forms of protection.
Three Lord Howe woodhens (Gallirallus sylvestris) on the forest floor of Lord Howe Island, Australia.
Credit: Toby Hudson / Wikimedia Commons, CC BY-SA 3.0 AU.
One example comes from Lord Howe Island, Australia. By the late 1970s, only 23 Lord Howe woodhens remained, flightless ground-dwelling birds. Thanks to conservation efforts, their population now exceeds 1,600 individuals.
Some species may be more difficult to save than others, depending in particular on their habitat and the threats they face.
A very real risk remains: when survivors are extremely few, breeding between close relatives can weaken subsequent generations. Nevertheless, the researchers emphasize that an extremely low initial population should not by itself be enough to condemn a species.