MONDAY, June 23 (HealthDay News) -- If you ever happen to hear crocodile eggs calling out to you, you're not imagining things.
These pre-hatching calls are produced by baby Nile crocodiles as messages to each other and to their mother, according to French researchers. They concluded that the calls tell others in the nest to hatch, and also tell the mother to start digging up the nest.
The study is the first to confirm what had only been suspected on the basis of prior observation, said researchers Amelie Vergne and Nicolas Mathevon of Universitie Jean Monnet, who believe this calling -- which sounds like "umph! umph! umph!" -- may be critical to the early survival of the baby crocodiles.
"We can well suppose that hatching synchrony can be of vital importance for crocodiles," Mathevon said in a prepared statement. "Indeed, most mortality occurs early in life and hatching vocalizations might well attract predators. Therefore, adult presence at the nest and its response to juvenile vocalizations may offer protection against potential predators. In this sense, it is important for all embryos in the nest to be ready for hatching at the same time so that they all receive adult care and protection."
For this study, the researchers divided a clutch of crocodile eggs that were due to hatch within 10 days into three groups. One group was played recordings of pre-hatching calls, one group was played recordings of noise, and one group was left in silence.
The baby crocodiles who heard the pre-hatching calls answered back. When it was time to hatch, all the babies hatched while the recording was played or within 10 minutes of it. This did not occur in the other groups.
The researchers also played recordings of pre-hatching calls to 10 female crocodiles in a zoo. The females' eggs had been removed after laying. A loudspeaker was placed in or near the empty nest and recordings of pre-hatching calls, interspersed with noise, were played at the end of the normal incubation period.
The females turned their heads or moved more often after they heard the pre-hatch calls than after they heard noise. Eight of the 10 females responded to the pre-hatching calls by digging, the researchers said.
The study was published in the June 23 issue of the journal Current Biology.
The Honolulu Zoo has more about Nile crocodiles.