In 2013, more than 70 of the species died in unexplained circumstances, thought to be related to a toxic agent, Radio New Zealand International reports . "The sad thing is now we are seeing the flow-on effect from that," says Brett Gartrell from Massey University, which tested the dead penguins for toxins. "There aren't a lot of birds around to breed at the moment - and that's what the yellow-eyed population desperately needs."