Interesting article by the Guardian on how dwindling numbers of the regent honeyeater are affecting the social behaviour of the species and particularly it's singing: How an endangered Australian songbird is forgetting its love songs And another on the BBC on the same topic : Regent honeyeater: Endangered bird 'has forgotten its song'
Yes and it does make you wonder how many more bird species out there are also experiencing this behavioural phenomena.
I always understood that birds begin learning the parents calls and songs whilst still in the egg, before hatching. Studies by CSIRO scientists in the 1960s indicated this. This species obviously have the ability to mimic other species, as do many others, so what is strange about hearing these calls? Satin bowerbirds and Lyrebirds come to mind, as they usually have a wide range of calls and songs of other species
I think this kind of learning that you mention does happen but with songbirds and the complexity of their calls some of this learning must occur as the fledgling matures and leaves the nest and parents and encounters other individuals of the species.
I have raised a variety of finches and cannot say they learn any of their songs before fledging age and mostly learn them in a period of about 6-8 weeks post weaning. If separated from the parent species too soon, they develop abnormal songs or copy other species of bird.
Songbirds can be divided into closed-ended learners and open-ended learners. The former don't change their song once it is completely crystallized. Zebra finches for example have a fixed learning period and repeat the same song the rest of their lives. The latter can continue to change their song as long as they live. Common nightingales are a good example, they broaden their repertoire as they get older. In a way, bird song is like human speech. There's an innate urge to produce sound, but both bird and human need a tutor to successfully sing and talk respectively. In zebra finches, the main model species for birdsong, the father is usually the tutor, though there's some influence from peers. Interestingly, female preference is also partly learned from a tutor or peers in zebra finches. Because birdsong is a cultural trait, it can show substantial spatial variation. One can imagine that with large-scale changes in distribution and abundance, cultural traits like birdsong also change accordingly. If local populations disappear or individuals from different populations are introduced, local dialects can go extinct. If this happens fast enough and over the substantial parts of the distribution of the species, one can image a huge loss in cultural variation. The honeyeater is obviously an exceptional case, but I wouldn't be surprised if this happened in some form already to many species that have experienced range contractions.
Just saw this in the Guardian, a follow up article on efforts to "teach" captive regent honeyeaters at zoos and captive breeding centers: Hitting the right note: why endangered Australian songbirds are being taught to sing in captivity
