The Bronx Zoo's Waldrapp ibis population just got bigger. Apparently the feathered flock hadn't been reproducing for the past seven years, but now zookeepers have found the magic formula to get the endangered birds to mate. According to the Daily News, mating calls recorded halfway around the world were played on an iPod in their space, and since then they've hatched six new offspring.

The zoo's ornithologist, Mark Hofling, says the entire species is at risk, and "they had pretty much stopped courtship behavior," and don't usually reproduce in captivity. Recordings of the mating calls had been made before, but all from zoos; this time around they went to visit a semiwild flock in Austria where they captured three mating calls (described as a chirrup, a whoop whoop and a shrum shrum).

As the ibis get a new soundsystem put into place, the zoo is considering a similar test for Caribbean and Chilean flamingos.