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Previous sections suggest that songbirds learn whole songs from their tutors. Marler and Peters (1987), however, propose that songbirds learn parts or elements of songs from various tutors and fuse them together to form their own unique song. Although there is some debate regarding this topic, recent research all seem to support that songbirds learn complete song types (Beecher 1996, described in Nordby et al. 2000; Nordby et al. 2000; Nordby et al. 2001).
The previous sections also hint that songbirds are exposed to and memorize more songs that they keep for their final repertoire. As explained before, while they are young, juveniles amass a great number of songs and goes through a selection process to weed out the songs they do not need once they are more mature (regardless of whether they continue to learn new songs during this time or not). There are two social ways for a juvenile songbird to learn and select songs. One is by directly interacting with an adult tutor; the other is by eavesdropping on singing interaction between two other birds.
As noted throughout the previous sections, interacting with a tutor (i.e. receiving countersinging feedback) leads to better song learning in juvenile songbirds than no interaction.
Eavesdropping is another important tool used by songbirds to learn songs, and is perhaps even more important than direct interaction. Juvenile song sparrows learn more by eavesdropping on an adult teaching another juvenile than by directly interacting with a tutor (Beecher et al. 2007). Furthermore, during the song-learning phase, juvenile song sparrows are more attracted to countersinging interactions between two or more birds than to the singing of a single bird (Templeton et al. 2010). The eavesdropping hypothesis explains these observations. As described in Burt et al. (2007), the eavesdropping hypothesis states that one of the advantages of eavesdropping over direct interaction is that by observing countersinging interactions, a juvenile bird can pay attention to both sides of the interaction and pick out the dominance relationship (Beecher&Burt 2004). The juvenile can then decide to learn the song of the more dominant bird. The juvenile can also use this dominance information in the future to make decisions regarding challenging other males. Furthermore, a juvenile bird can learn how to reply appropriately to certain songs. The eavesdropping hypothesis predicts that a juvenile bird will not only learn songs from a chosen tutor, but also from birds that sing to the tutor (Burt et al. 2007). Eavesdropping, therefore, is an important adaptive trait that allows songbirds to not only learn songs, but to learn ones that are most beneficial for their fitness.
Now, having described song learning in songbirds, we can compare it to speech learning in humans. Marler (1970a) is one of the first to argue that birdsong learning parallels human speech learning. He compares babbling in infants to subsongs in birds in that both are initial, elastic precursors to their final forms of vocalization. Also, both infants and songbirds have a preference for learning conspecific vocalizations and both use vocal imitation and auditory feedback in the learning process. Furthermore, both infants and songbirds seem to derive some sort of intrinsic reward for imitating they sounds they hear with vocalizations (Marler 1970a).
In addition, speech learning in humans has a large social component, just like song learning in birds (see previous discussions). Golstein et al. (2003) performed speech experiments on 8-month old human infants, who are at a speech developmental stage that parallels the subsong developmental stage in songbirds (see [link] ). They found that infants that received immediate social feedback after a vocalization showed a significant increase in the number and quality of vocalizations. Meanwhile, infants that received the same amount of random social feedback (not necessarily after a vocalization) showed an increase in number but not quality of vocalizations. These results show that social feedback can affect speech development, just like song development (Goldstein 2003).
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