Brazil's Atlantic Forest may be dwarfed by the much larger Amazon, but it's still surprisingly biodiverse for its size. It once spanned three times the size of California, until humans cleared about 85 percent of it over the past 500 years. Species that evolved with plenty of space are now trapped in shrinking fragments of forest.

Miraculously, these fragments still hold 2,200 species of birds, mammals, reptiles and amphibians, representing 5 percent of all vertebrates on Earth. That includes nearly 200 bird species and 21 primates that exist nowhere else, yet despite such unique biological wealth, only about 2 percent of the Atlantic Forest is under protection.

In one isolated fragment, however, a small nature preserve has just grown by nearly 50 percent, thanks to conservationists working to save its array of wildlife from extinction. Known as Mata do Passarinho — Portuguese for "Songbird Forest" — this patch of Atlantic Forest has expanded to add 766 new acres, raising its total area from 1,586 to 2,352 acres, or 9.5 square kilometers. That may not sound like much, but in a forest this biodiverse and this endangered, almost every inch matters.

Mata do Passarinho ReserveA view of the Songbird Forest, located in the Brazilian states of Minas Gerais and Bahia. (Photo: Fundação Biodiversitas)

Due to deforestation, Mata do Passarinho "is like an oasis in a desert," says Gláucia Drummond, director of the Brazilian conservation group Fundação Biodiversitas. That "desert" is mostly farmland and cattle pasture surrounding the Songbird Forest, making it one of the last bits of Atlantic Forest in northern Minas Gerais and southern Bahia (see map below). It's now the southern frontier of a fading forest biome, sheltering rare species in a space that would fit inside some large city parks.

Mata do Passarinho map

As its name suggests, the forest is a haven for songbirds, many near extinction. Its most at-risk species is the critically endangered Stresemann's bristlefront, whose estimated 15 survivors all live in Mata do Passarinho. Not only are they the reserve's rarest birds; they're one of the most endangered animals anywhere.

The Stresemann's bristlefront (pictured below) is named after the long, bristly feathers that protrude from its forehead. It nests in underground tunnels and is famously elusive, first documented in the 1830s but not again until 1945. A third sighting came in 1995 near Una Biological Reserve in southern Bahia, although none have been seen there since. The birds' remaining population was finally found in 2004, in an unprotected area that would later become Mata do Passarinho.

Stresemann's bristlefrontA male Stresemann's bristlefront in Mata do Passarinho, the species' last-known refuge. (Photo: Ciro Albano)

The reserve was established in 2007 by Fundação Biodiversitas, with help from the American Bird Conservancy (ABC), and both groups again collaborated on its new annex. The bristlefronts are still in dire straits, but according to ABC vice president Daniel Lebbin, these 766 extra acres do brighten their outlook significantly.

"With this acquisition, the Mata do Passarinho Reserve now protects all the forest known to be occupied by the Stresemann's Bristlefront," Lebbin says in a statement issued by the bird conservancy. "Additional expeditions are needed to confirm if any other bristlefronts may still persist in additional forest fragments nearby."

Here's a rare video of both male and female Stresemann's bristlefronts, released in 2012 by Brazilian photographer Ciro Albano:

Beyond bristlefronts, the Songbird Forest also hosts several other endangered birds on the IUCN Red List, including the banded cotinga, brown-backed parrotlet, red-browed parrot, hook-billed hermit and Bahia tyrannulet. By giving these birds more space to nest and forage, the expansion is meant to be a rising tide that lifts all boats. Or, to adapt a more relevant idiom, it could save lots of birds with one stone.

red-browed parrot, Amazona rhodocorythaOnly 1,000 to 2,500 red-browed parrots are left on Earth, some of which inhabit the Songbird Forest. (Photo: Shutterstock)

And while birds are a key reason this forest is protected, they're hardly the only beneficiaries of its expansion. Mata do Passarinho is home to rare mammals, too, like the maned three-toed sloth and the yellow-breasted capuchin monkey (aka golden-bellied or buff-headed capuchin), which is listed as critically endangered by the IUCN.

yellow-breasted capuchin, Sapajus xanthosternosHunting and habitat loss have shrunk yellow-breasted capuchin populations by 80 percent in 50 years. (Photo: Shutterstock)

Plant diversity is another strength of Atlantic Forest fragments like this, since about 20,000 different plant species still exist across the biome. That's roughly 8 percent of Earth's plants, according to the Nature Conservancy, which notes that one study counted 458 types of trees in a single 2.5-acre section of Atlantic Forest — more than double the number of tree species found across the entire U.S. Eastern Seaboard.

Plus, as with most nature reserves, fortifying the Songbird Forest is good for people as well as wildlife. There are the broad health benefits of forest bathing, for instance, and possible brain boosts from the sound of birdsong. Atlantic Forest remnants can also help ensure valuable ecological services for humans, including clean air, clean water, erosion control, bee pollination and resources like wood, food or medicine. And given the allure for birdwatchers seeking life birds, conservationists are especially optimistic about Mata do Passarinho's eco-tourism potential.

"We want the reserve to be a source of pride for local communities and for public managers as well as being an opportunity to generate income for these people and municipalities," Drummond says. "The challenge now is to raise awareness among neighboring landowners about local production practices and help them understand the importance of maintaining and restoring native forest."

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.