A word in your shell: how crocodiles tell each other when to hatch

view gallery VIEW GALLERY

A A A

To the human ear they sound like the tinny thud of a small starter motor, but to a mother crocodile they are the plaintive calls of her egg-bound babies, saying they are about to hatch en masse and could she please make sure there are no nasty predators nearby.

The "umph, umph, umph" calls of unhatched crocodiles have been shown by scientists to be vital vocal signals that co-ordinate their entry into the world.

For the first time, researchers have shown that the pre-hatching calls of baby Nile crocodiles actually mean something to their siblings – and to their mothers. The calls serve the essential function of telling others in the nest that it is time to hatch, as well as warning their mother to protect them, said Amélie Vergne and Nicolas Mathevon of Université Jean Monnet in Saint-Etienne, France.

The behaviour may have a long history, the researchers said. Birds also produce "embryonic vocalisations" that induce parental care. Such early communication may be a shared behavioural feature of past and present members of the Archosaurs, an ancient group of reptiles now represented by modern birds and crocodiles.

The study used recordings of the sounds made by unhatched baby crocodiles in their underground nests. It demonstrated that mothers show signs of caring behaviour.

"Hatching synchrony can be of vital importance for crocodiles," said Dr Mathevon. "Indeed, most mortality occurs early in life and hatching vocalisations might well attract predators.

"Therefore, adult presence at the nest and its response to juvenile vocalisations 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."

The calls tell the mother crocodile to start digging up the nest, according to the study published in the journal Current Biology, which was based on a "playback" experiment.

Crocodilians were known to make sounds within the egg shortly before hatching, the researchers said. To find out what those calls might mean in the new study, the researchers divided crocodile eggs that were due to hatch within 10 days into three groups. One of those groups was played recordings of pre-hatching calls, one was played recordings of noise, and the last was left in silence until they hatched.

The eggs played the pre-hatch sounds more often answered back, they report, and many moved. All of the eggs in the pre-hatch group hatched during the playback or within 10 minutes of it. Whereas only once did the eggs hearing general noise hatch. The rest hatched at least five hours after the last test.

The researchers then tested the mothers' responses to the calls. "In the zoo where we did the experiments, eggs were 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 10 mothers. The adults more often turned their heads or moved after egg sounds than after noise, they showed, and eight of the mothers responded to the recorded calls by digging.

The same scientists have previously analysed 400 calls made by 10 young crocodiles during their first four days after hatching. They found that the calls have a "complex acoustic structure", but individual baby crocodiles do not appear to have distinctive calls – so that mothers are unlikely to recognise the calls of their own young compared to the calls of another's offspring.

It is only relatively recently that scientists have confirmed that crocodiles engage in fairly extensive maternal care. It was originally thought that they simply laid their eggs and did not get involved in either protecting them or the hatchlings.

Suggested Topics
News
peopleJonathan Ross has got a left-field suggestion to replace Clarkson
News
Andy Davidhazy at the beginning (left) and end (right) of his hike
video
Arts and Entertainment
The teaser trailer has provoked more questions than answers
filmBut what is Bond's 'secret' that Moneypenny is talking about?
News
Johnny Depp is perhaps best known for his role as Jack Sparrow in Pirates of the Caribbean
peopleBut how did he break it?
Have you tried new the Independent Digital Edition apps?
Sport
Lewis Hamilton secured his second straight pole of the season
f1Vettel beats Rosberg into third after thunderstorm delays qualifying
Arts and Entertainment
Written protest: Julia Donaldson, author of The Gruffalo, has sent an open letter to the Culture Secretary
books
Travel
travel Dreamland Margate, Britain’s oldest amusement park, is set to reopen
News
news
News
Founders James Brown and Tim Southwell with a mock-up of the first ever ‘Loaded’ magazine in 1994
media
  • Get to the point
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
iJobs Job Widget
iJobs General

Ashdown Group: Practice Accountant - Bournemouth - £38,000

£32000 - £38000 per annum: Ashdown Group: A successful accountancy practice in...

SThree: Trainee Recruitment Consultant

£18000 - £23000 per annum + Uncapped commission: SThree: Does earning a 6 figu...

Recruitment Genius: SEO Executive

£18000 - £25000 per annum: Recruitment Genius: This is an exciting opportunity...

Recruitment Genius: New Lift Sales Executive - Lift and Elevators

£35000 - £40000 per annum: Recruitment Genius: A challenging opportunity for a...

Day In a Page

The saffron censorship that governs India: Why national pride and religious sentiment trump freedom of expression

The saffron censorship that governs India

Zareer Masani reveals why national pride and religious sentiment trump freedom of expression
Prince Charles' 'black spider' letters to be published 'within weeks'

Prince Charles' 'black spider' letters to be published 'within weeks'

Supreme Court rules Dominic Grieve's ministerial veto was invalid
Distressed Zayn Malik fans are cutting themselves - how did fandom get so dark?

How did fandom get so dark?

Grief over Zayn Malik's exit from One Direction seemed amusing until stories of mass 'cutting' emerged. Experts tell Gillian Orr the distress is real, and the girls need support
The galaxy collisions that shed light on unseen parallel Universe

The cosmic collisions that have shed light on unseen parallel Universe

Dark matter study gives scientists insight into mystery of space
The Swedes are adding a gender-neutral pronoun to their dictionary

Swedes introduce gender-neutral pronoun

Why, asks Simon Usborne, must English still struggle awkwardly with the likes of 's/he' and 'they'?
Disney's mega money-making formula: 'Human' remakes of cartoon classics are part of a lucrative, long-term creative plan

Disney's mega money-making formula

'Human' remakes of cartoon classics are part of a lucrative, long-term creative plan
Lobster has gone mainstream with supermarket bargains for £10 or less - but is it any good?

Lobster has gone mainstream

Anthea Gerrie, raised on meaty specimens from the waters around Maine, reveals how to cook up an affordable feast
Easter 2015: 14 best decorations

14 best Easter decorations

Get into the Easter spirit with our pick of accessories, ornaments and tableware
Paul Scholes column: Gareth Bale would be a perfect fit at Manchester United and could turn them into serious title contenders next season

Paul Scholes column

Gareth Bale would be a perfect fit at Manchester United and could turn them into serious title contenders next season
Inside the Kansas greenhouses where Monsanto is 'playing God' with the future of the planet

The future of GM

The greenhouses where Monsanto 'plays God' with the future of the planet
Britain's mild winters could be numbered: why global warming is leaving UK chillier

Britain's mild winters could be numbered

Gulf Stream is slowing down faster than ever, scientists say
Government gives £250,000 to Independent appeal

Government gives £250,000 to Independent appeal

Donation brings total raised by Homeless Veterans campaign to at least £1.25m
Oh dear, the most borrowed book at Bank of England library doesn't inspire confidence

The most borrowed book at Bank of England library? Oh dear

The book's fifth edition is used for Edexcel exams
Cowslips vs honeysuckle: The hunt for the UK’s favourite wildflower

Cowslips vs honeysuckle

It's the hunt for UK’s favourite wildflower
Child abuse scandal: Did a botched blackmail attempt by South African intelligence help Cyril Smith escape justice?

Did a botched blackmail attempt help Cyril Smith escape justice?

A fresh twist reveals the Liberal MP was targeted by the notorious South African intelligence agency Boss