Olive trees are sprouting all across the Balearic Islands—a chain off the Mediterranean coast of Spain. The largest island, Mallorca, has more than 800,000 cultivated trees. They yield a good portion of the world’s supply of extra virgin olive oil.

More trees—of both wild and cultivated varieties—have been showing up on the surrounding islands. They’ve been planted not by farmers, but by sea gulls. The gulls eat olives—especially those from Mallorca—then fly miles over the Mediterranean to their home islands. Once there, they spit up the olive pits, which can sprout and grow trees.

Biologists recently studied yellow-legged gulls, which are common across the Balearic Islands. The scientists brought some of the birds into the lab, and attached GPS trackers to others. They also examined the populations of olive trees in the islands.

The researchers found that the birds ate both wild and cultivated olives. But they preferred the ones raised on farms. On average, they flew about three miles farther to get them—about eight miles per trip, although some gulls flew more than 60 miles.

The gulls upchucked most of the olive pits on the rocky outcrops where they nest. But many of the pits were dropped where they could produce trees. On one island, an area that had been mostly grass and shrubs was being transformed into an olive grove, with both wild and domestic varieties—thanks to the wings and appetites of yellow-legged gulls.