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April 29, 2009
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From the egg, baby crocs call out
June 23, 2008
Courtesy Cell Press
and World Science staff
Baby Nile crocodiles’ pre-hatching calls actually mean something to their siblings and mothers, researchers have found. A hatching crocodile. (Image
courtesy U.S. Geological Survey)
The calls—which are perfectly audible to humans and sound like “umph! umph!”—tell the other
youngsters it’s time to hatch, and alert the mother to start digging up the nest, according to the group.
The findings, drawn from sound-playback experiments, confirm what some had suspected based on anecdote, according to the scientists, Amélie Vergne and Nicolas Mathevon of Université Jean Monnet in France.
The calling behavior may be key to the reptiles’ early survival, and their ability to hatch together of “vital importance,”
Mathevon speculated.
“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…. 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.”
The researchers divided crocodile eggs due to hatch within 10 days into three groups. One group was played recordings of pre-hatching calls; one was played recordings of noise; and the last was left in silence.
The eggs played the pre-hatch sounds more often answered back, the experimenters reported. Many of the eggs in that group also moved. Finally, the researchers said, all of the eggs in the pre-hatch group hatched during the playback or within 10 minutes of it. Only once did the eggs hearing noise hatch, and the rest hatched at least five hours after the last test.
The scientists then tested the mothers’ responses to the calls. In the zoo where the experiments were carried out, eggs are removed from the nest within a few days
of laying, the researchers explained. In spite of this, females continue to guard the nest.
At the end of the incubation period, the researchers hid a loudspeaker underground near the empty nest. They then played pre-hatching calls interspersed with noise to ten mothers. The adults more often turned their heads or moved after egg sounds than after noise, they noted, and eight of the mothers responded to the recorded calls by digging.
The findings appear in the June 23 issue of the research journal
Current Biology.
The behavior may have a long history, the researchers said.
“As birds also produce embryonic vocalizations that induce parental care,” they wrote, “such acoustic communication at an early stage of development may be a shared behavioral feature of past and present
archosaurs.” Archosaurs are an ancient group of reptiles now represented by modern birds and crocodiles.
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Baby Nile crocodiles’ pre-hatching calls actually mean something to their siblings and mothers, researchers have found. The calls—perfectly audible to humans, and which sound like “umph! umph! umph!”—tell the other infants it’s time to hatch, and alert the mother to start digging up the nest, according to the group. The findings, drawn from sound-playback experiments, confirm what some had suspected based on anecdote, according to the scientists Amélie Vergne and Nicolas Mathevon of Université Jean Monnet in France. The calling behavior may be key to the reptiles’ early survival, and their ability to hatch together of “vital importance,” Mathevon speculated. “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…. 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.” The researchers divided crocodile eggs due to hatch within 10 days into three groups. One group was played recordings of pre-hatching calls; one was played recordings of noise; and the last was left in silence. The eggs played the pre-hatch sounds more often answered back, the experimenters reported. Many of the eggs in that group also moved. Finally, the researchers said, all of the eggs in the pre-hatch group hatched during the playback or within 10 minutes of it. Only once did the eggs hearing noise hatch, and the rest hatched at least five hours after the last test. The scientists then tested the mothers’ responses to the calls. In the zoo where the experiments were carried out, eggs are removed from the nest within a few days following the laying date, the researchers explained. In spite of this, females continue to guard the nest. At the end of the incubation period, the researchers hid a loudspeaker underground near the empty nest. They then played pre-hatching calls interspersed with noise to ten mothers. The adults more often turned their heads or moved after egg sounds than after noise, they noted, and eight of the mothers responded to the recorded calls by digging. The behavior may have a long history, the researchers said. “As birds also produce embryonic vocalizations that induce parental care,” they wrote, “such acoustic communication at an early stage of development may be a shared behavioral feature of past and present Archosaurs.” Archosaurs are an ancient group of reptiles now represented by modern birds and crocodiles. The findings appear in the June 23 issue of the research journal Current Biology.