The Female Bird Song Project team released a comprehensive survey of female bird song in 2014. They researched documentation of female song in different species and arrived at a 92 percent likelihood that the oldest shared ancestor of the song birds we hear today had female singers. This finding spurred them to investigate why female and male birds have been singing all this time and which ecological factors played key roles in the evolution of their songs. Leiden biologist and principal investigator Dr. Katharina Riebel says territoriality, migration and mating systems might be the most important factors to focus on. “But, “ she says, “we urgently need more field studies looking at the context in which females produce song,”