The Pale-headed Brushfinch was rediscovered in west-central Ecuador almost 25 years ago — following three decades without a record of the species. The expedition that found this “lost” bird was spearheaded by Fundación de Conservación Jocotoco with American Bird Conservancy (ABC) support. Unfortunately, at the time, the species numbered only about 15 pairs. And as far as anyone knew, the Pale-headed Brushfinch only occurred on about 60 acres — an area the size of one or two U.S. high school campuses.
Jocotoco and ABC immediately began conservation efforts by acquiring, protecting, then improving habitat for the brushfinch. Over the past few decades, the bird’s story has become a shining example of how, even in a small area, a species can be saved from extinction by following clear-headed strategy based on sound research.
In 2021, the total population was estimated to have grown to about 240 individuals, with 112 known territories. All told, Jocotoco and ABC, along with Rainforest Trust, have protected about 485 acres of brushfinch habitat. As a result of these actions, the species was downlisted on the International Union for Conservation of Nature’s Red List from critically endangered to endangered. It appears, for the Pale-headed Brushfinch, an area of 485 acres has been sufficient to prevent its extinction.
But some birds need much more space to thrive. How do biologists know how much habitat is enough? Obviously, it must be enough to provide a place for an adequate population of the species to thrive. One rule of thumb that conservationists have long used is a minimum population size of 500 individuals. This number is thought to provide for enough genetic diversity that inbreeding can be avoided, and it provides a buffer to allow the population to survive a loss in bad years.
Scientists are now making these habitat calculations with the Pale-headed Brushfinch’s cousin, the Antioquia Brushfinch. This songbird was rediscovered near Medellín, Colombia, in 2018 and is now considered critically endangered. Field research has revealed that Antioquia Brushfinches survive in shrubby natural habitats. The next conservation challenge is to determine the bird’s potential range and apply the “500” rule of thumb to determine how much land should be protected to ensure its survival.
Habitat is the key for every species, and it is always a challenge to know how much is enough. But through collaboration, modern science, and a broad range of ways to conserve land, we continue to craft conservation recipes that help to save the rarest of the rare. — David A. Wiedenfeld
David A. Wiedenfeld is the senior conservation scientist with American Bird Conservancy. This article appears in the January/February 2023 issue of BirdWatching magazine.