Pigs with warts the size of a grapefruit

Male Bawean warty pigs have whopping warts on their faces, and nobody knows why

The south-east Asian archipelago is pig paradise. This region hosts the highest wild pig diversity in the world.

That is probably because rising and falling seas have connected and disconnected this large scattering of islands for over 5 million years. When animals become isolated on islands, new species can evolve, and that seems to be what has happened here with pigs.

One of the products of evolution gone hog wild is the little-known Bawean warty pig. It is found only on the island of Bawean, the remnant of an extinct volcanic mountain in Indonesia's Java Sea.

Until now, scientists did not even know how many of these pigs there were.

The Bawean Island warty pig is so named because the typical male has "three pairs of enormous warts on each side of its face," says Johanna Rode-Margono, a researcher at Chester Zoo in the UK and a member of the IUCN/SSC Wild Pig Specialist Group.

Nobody knows why the males have these grapefruit-sized warts.

"There are various different theories," says Rode-Margono's colleague Eric Meijaard, the founder of Borneo Futures and chair of the IUCN/SSC Wild Pig Specialist Group. "It could be a display function," meaning that nice-looking warts might be a means for males to impress the females. Alternatively, the warts could play a role in fighting or defence. "Wild boars fight each other by slashing with their lower tusks, and the warts would protect the face, especially the eyes," says Colin Groves of the Australian National University.

In addition to their oversized warts, some male Bawean warty pigs have white beards and large tufts of golden hair fanning out from both sides of the head. Again, it is unclear why.

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