The elusive tree kangaroo lives in the leafy canopy of Australia's rainforests. Phil visits a rehabilitation centre for these tree-dwelling marsupials and learns that they're very fussy eaters. They prefer rainforest leaves with high levels of toxins and have a special adaptation where their gut bacteria ferment and break down toxins so the leaves can be digested. Watch Built to Survive from Monday May 5th at 7pm, on National Geographic WILD UK. | National Geographic UK