Nestling begging calls resemble maternal vocal signatures when mothers call slowly to embryos

Vocal production learning (the capacity to learn to produce vocalizations) is a multi-dimensional trait that involves different learning mechanisms during different temporal and socio-ecological contexts. A key outstanding question is whether vocal production learning begins during the embryonic stage and whether mothers play an active role in this through pupil-directed vocalization behaviors. We examined variation in vocal copy similarity (an indicator of learning) in eight species from the songbird family Maluridae, using comparative and experimental approaches. We found that: (1) incubating females from all species vocalized inside the nest and produced call types including a signature ‘B element’ that was structurally similar to their nestlings’ begging call; (2) in a prenatal playback experiment using superb fairywrens (Malurus cyaneus), embryos showed a stronger heart rate response to playbacks of the B element than to another call element (A); and (3) mothers that produced slower calls had offspring with greater similarity between their begging call and the mother’s B element vocalization. We conclude that malurid mothers display behaviors concordant with pupil-directed vocalizations and may actively influence their offspring’s early-life through sound learning shaped by maternal call tempo. 

Methods
We placed microphones near the nests of eight species of Maluridae to record incubating female in-nest calls. Across species, we identified up to four element types and in all species, every female produced a signature B element. We calculated female element rate as the number of elements per s. We recorded the chicks' B element begging calls after hatching and used spectrographic cross-correlation analysis to compare vocal copy similarity between the mother's B element and the offspring's B element. We used an experimental approach in superb fairywrens and broadcast calls with different numbers of A and B elements, and measured embryo response to calls with different numbers of A and B elements using change in heart rate as the response variable.