MANILA: Luzon may be known as the largest and most populous island of the Philippines, but it is also home to the greatest concentration of unique mammal species on Earth. Most of them are found nowhere else in the world.

The island, where the Philippine capital Manila is located, had never been connected to any continental land. Throughout the ages, this allowed the species that arrived there from the Asian mainland to evolve, diversify, and thrive in different habitats of its mountain ranges and peaks isolated by lowlands.

It is also one of the oldest islands, with geological research indicating that parts of it have been dry land areas continuously for some 27 million years.

“It’s a really old island. So, there’s time for rare events to take place. That’s a big part of it,” Dr. Lawrence Heaney, biologist and curator of mammals at the Field Museum in Chicago, told Arab News.

“There are no countries in continental Europe that have (this number of) unique species of mammals.”

Heaney is one of the first researchers to document the island’s diversity and has been leading American and Filipino scientists studying mammals in the Philippines since 1981.

His team’s 15-year study, which started in 2000, concluded that there were 56 species of mammals — not including bats — on the island, and 52 of them were endemic.

This means that 93 percent of Luzon’s non-flying mammals are found nowhere else, making it a biological treasure trove.

Luzon beats even the Galapagos islands, where each has been known for its diverse and unique array of wildlife.

“Luzon takes it another step further because there are isolated mountain ranges and isolated mountain peaks that are separated from all others by lowlands. They function as islands. Islands in the sky. Each one of those islands in the sky has its own unique set of species. Luzon island is made up of islands within the island,” Heaney said.

“What’s in the northern Sierra Madre, you know Cagayan province ... is very different from what’s in the mountains that are in Aurora province, because there’s an area of lowlands that separates those two different mountain chains. Then the mountains, the next set of mountains down also are separated by another low-lying area ... There are species of mammals that occur there that don’t live anywhere else in the world.”

Many of those mammals are tiny — the size of the house mouse. When most people think about mammal species, they usually imagine those on the larger part of the spectrum, like themselves.

“We think about water buffalo and horses and lions and tigers and bears,” Heaney said. “There are actually very few large mammals, overwhelmingly, most mammals are small, less than 200 grams ... Not surprisingly, given that, most of the things that we have discovered that were previously unknown are small.”

Mariano Roy Duya, associate professor at the University of the Philippines’ Institute of Biology, who has been working with Heaney, told Arab News that 28 out of the 56 mammal species identified in Luzon were rodents.

Two of them — the Banahaw shrew rat and the Banahaw tree mouse — were endemic to Mt. Banahaw, which is only 100 km from Manila.

The Banahaw shrew-rat has a long, slender snout, a short tail, and weighs 150 grams, while the Banahaw tree mouse is the smallest member of the cloud rat family at 15.5 grams, and navigates tree branches and vines.

Their habitat is now protected due to the efforts of the Biodiversity Conservation Society of the Philippines, a group that was created thanks to the work of scientists like Heaney and Duya, who now serves as its vice president.

The society is an organization that the Philippine Department of Environment and Natural Resources consults on the country’s conservation efforts.

Some 20 percent of the species Heaney, Duya, and other researchers studied during their long Luzon project are vulnerable, endangered, or critically endangered due to habitat loss, hunting, and illegal wildlife trade.

“(These include) deer, warty pigs, cloud rats, flying foxes, cave-dwelling bats, and civets,” Duya said.

“According to the hunters we meet in the forest, these animals are becoming hard to find.”

Most of the threats to Luzon’s wildlife were observed in lowland forests, which are usually lost to human development, overlogging, conversion to agricultural fields, and trafficking.

“Close monitoring of illegal wildlife trade and regular enforcement activities should be a priority,” Duya said.

“Securing these forests, as well as forest fragments, will provide refuge to many of these endemic faunae.”