Christopher Tracy found the three radio transmitters lying on the forest floor. They were still intact and sending off a strong signal, but there was a big problem – all three of them were meant to be inside the body of a frog.
Several weeks before, Tracy had implanted transmitters into three species of Australian frogs to track their whereabouts. He had placed the devices into the frogs’ peritoneal cavity, a space within its belly that contains its stomach, guts and liver. But these ones were alone, with no bodies nearby or any signs of predators. The frogs hadn’t died or been eaten, but they had somehow removed the transmitters from an enclosed space within their bodies.
When Tracy located his other tagged frogs, he found an important clue: around three-quarters of the transmitters had moved to the animals’ bladders. Tracy was intrigued. He rounded up five more Australian tree frogs and five cane toads, implanted small beads into their bodies, and tracked them solidly for two to three weeks. After that time, he found that four of the toads had the beads in their bladders, and the other animals had urinated theirs out.