SUPERB FAIRY-WRENS (Malurus cyaneus) sing to their eggs passing on a password to their chicks in the embryonic stages to help identify them from Horsfield's Bronze Cuckoo (Chalcites basalis) nestlings.
The research, Embryonic Learning of Vocal Passwords in Superb Fairy-Wrens Reveals Intruder Cuckoo Nestlings has been recently published in the journal Current Biology.
Investigators discovered that incubating female wrens were ‘singing’ to their eggs by making a previously unknown vocalisation—dubbed ‘incubation call’.
According to head researcher, Professor Sonia Kleindorfer, the password has been isolated to a single note and is specific to the nesting family.
Once born the hungry chicks are expected to sing the same tune back to their mother before being fed.
Parents will only feed chicks if their begging calls contain the password, if not the parents will abandon the nest and start again, says Prof Kleindorfer.
Superb fairy-wrens’ nests are frequently parasitised by several cuckoo species and while they may incubate the eggs it was found wren mothers used their secret tune as an identification process—refusing to feed chicks with foreign nestling calls.
The password is taught in the late stages of incubation.
Cuckoo eggs hatch earlier and are therefore given less time to learn the secret code.
By making a series of recordings researchers found that the chicks’ begging calls were significantly similar to a short element within the female’s incubation call resulting in a unique vocal password for each wren family.
To keep their password ‘secret’ data suggests that a specific female fairy-wren’s incubation call was never recorded after the eggs hatched.
Cross-fostering experiments, in which clutches of eggs were swapped between nests, showed the nestlings produced begging calls that matched their foster mothers—evidence that the passwords were indeed learned.
Playback experiments showed that adults respond to the begging calls of offspring hatched in their own nest and less to calls of other wren or cuckoo nestlings.
According to Prof Kleindorfer, in systems with uni-parental care, caretakers of embryos have more opportunity to pass on female memes, or messages to the embryo.
Hence, mothers have an ability to transmit not just genes to the next generation but also memes.
The research concluded that the tune identification tactic wrens’ use may indeed have an evolutionary development, whereby, nest-begging calls may not entirely be innate or species-specific but actually learned.
“This discovery of pre natal learning changes the way we perceive mother–embryo communications in many species including humans,” says Professor Kleindorfer.