For seven years, the Waldrapp ibises living at the WCS Bronx Zoo produced no chicks. While the species rarely reproduces in captivity, the zoo's birds had a job to do. Only about 400 of their kind exist in the wild. The pressure was on. The birds, however, were seemingly unaware of this pressure, showing little interest in mating.
“They had pretty much stopped courtship behavior. They were just going through the motions,” said WCS ornithologist Mark Hofling, who leads the AZA Species Survival Program (SSP) for Waldrapp ibises in North America.

Zookeepers realized that if the zoo’s 21 birds were going to help their species to survive, they were going to need more encouragement. The encouragement came in the form of mood music.

What does mood music for a large, shiny, pink-headed bird sound like? Well, it sounds like this [link to MP3?] Loud and clear mating calls, of which there are three types: whoop whoop, chirrup, and shrum shrum.

Alan Clark of Fordham University began recording ibis mating calls at the WCS Bronx Zoo and the Philadelphia Zoo. The ibises were somewhat responsive, but still the birds’ musical tastes and breeding interest seemed finicky.

Finally this spring, Clark recorded the calls of a semi-wild population of Waldrapp ibises in Austria. Before habitat loss and pesticide use began taking their toll on the birds’ numbers, Waldrapp ibises lived in large colonies that nested on the sides of cliffs throughout the Mediterranean region. Presently, the birds only breed in the wild in Morocco and Syria, with Syria having just three breeding pairs.

Perhaps it was the vocalizations of a greater number of birds that was key to the Austrian recording’s success, but the sounds from the European flock seemed to do the trick for the Bronx birds.

In the end, an iPod, a set of speakers, and a special playlist snapped the birds out of their breeding rut. They mated, laid eggs, and produced six baby birds. Within six weeks, the ibis hatchlings grew to an adult weight of around two pounds.

“If it works with this one species, there’s the possibility we can apply it to a wider range,” said Nancy Clum, curator of birds at the Bronx Zoo. The zoo’s next album du amor will be for Caribbean and Chilean flamingoes.