For the hoolock gibbons of India’s Hoollongapar Gibbon Sanctuary, who don't like to spend time on the ground, a rail line has divided the 26 family groups for more than a century. Now a natural canopy bridge, formed by thousands of trees planted along the tracks, is linking them, so gibbons in the smaller area have more food and can mate with gibbons in the larger area. The trees were planted in 2006, and the gibbons began crossing over the tracks in 2019. Other species also are using the natural bridge. Despite the extra work, the railway department supports the bridge, and there are plans to build more such bridges.