Baby Birdies Babbling:

By late summer, one may begin to overhear garbled cacophonies of birdsong while out birding. From approximately August through until the following spring, “baby” songbirds “babble” as they take to learning and developing their songs. This long road to song crystallization, i.e. fully developed song, first begins with a period known as subsong. Subsong is akin to the babbling of infants and is an endearing attempt at singing. Often, subsong attempts are drawn-out and structureless. Take for example this lil’ baby Sedge Wren giving its song a-go: http://www.xeno-canto.org/211425. As a bird begins to work the kinks out, it advances to the following stage of development, known as the plastic song. At this stage, discreet song phrases emerge, as does a semblance of the final product, the fully crystallized song. A banner such as “not quite there yet, but keep trying!” is appropriate for birds in their plastic song phase. Take for example this White-throated Sparrow. The classic song is emerging, but there’s still some work to do. http://www.xeno-canto.org/33227.