Interesting


http://www.world-science.net/othernews/080622_crocs

Ba­by Nile croc­o­diles' pre-hatch­ing calls ac­tu­ally mean
some­thing to their sib­lings and moth­ers, re­search­ers have found.

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.

A hatching crocodile. (Im­age cour­tesy U.S. Geo­lo­gi­cal Sur­vey)
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