What kind of obsession drives illegal egg collectors to scale towering cliffs in pursuit of nests, face prison sentences and fines of up to £5000 ($7400), and risk endangering entire bird species? With his 2015 documentary Poached, British filmmaker and director Timothy Wheeler tried to find out.

Audubon magazine recently spoke with Wheeler, whose award-winning documentary profiles a few of England’s most notorious egg bandits. One of them, an unidentified man who goes by “Mr. X,” has amassed a collection of 3500 eggs. Another individual describes his habit as “an addiction comparable to a drug addiction.”

To obtain these eggs, the collectors will free-climb trees or rappel down steep rocks. Then, after obtaining their illegal treasures, they’ll stash them in safe houses or underneath floorboards. According to Wheeler, many of them are addicted to the rush of performing unlawful or extreme activities. They also take pride in their skills—after all, it isn’t easy to reach the top of a 100-foot tree.

The collectors are both obsessed with birds and rare finds—desires that are complicated by the fact that the scarcer the egg, the more threatened the species. Still, according to Audubon, Wheeler is careful not to villainize his subjects and instead frames their obsession in the broader category of addiction psychology. To learn more about their subculture, read Audubon's full interview online, watch a preview of Poached above, or check out the film when it’s released on iTunes on January 15th.

[h/t Audubon]