Cultural evolution of birdsong occurs when songs change over generations and such changes can spread directionally or via drift within and between populations. The objective of this thesis was to document the emergence and spread of a novel song variant, the Modulated-Doublet, within and between populations of White-throated Sparrows. I analysed songs recorded in a Prince George population between 2015-2020 to document song shift within the population. I also analysed songs from public song archives to document song transition on a continental-scale between 2014-2020. I found the Modulated-Doublet started as a rare variant but became the predominant variant within our population over a very short time. At the continental scale, the Modulated-Doublet emerged simultaneously and spread synchronously in multiple breeding populations and migratory routes, replacing the previous variant in those populations. This rapid spread at both scales suggests it is driven by several transmission biases; however further investigation is needed to determine their nature.
