Date of Award


Publication Type

Master Thesis

Degree Name



Biological Sciences

First Advisor

Daniel Mennill




Bird song is one of the most well studied animal communication systems, and yet there are many features left to be explored. In particular, recent studies have revealed subtle ontogenetic changes in the voice of birds after reaching adulthood. Furthermore, recent literature reviews have highlighted the long-overlooked importance of female song, and its parallels to male song in terms of complexity and function. In this thesis, I review the current literature on the topics of song ontogeny, crystallized song, and song as a signal of age. Then, I explore the potential for song to signal an animal’s age through a longitudinal study of a Neotropical songbird: the Rufous-and-white Wren. My analyses relied on 15 years of recordings of male and female Rufous-and-white Wren singing behaviour, collected during a long-term study of the behavioural ecology of a population living in northwestern Costa Rica. Focusing on the post-crystallization songs of the longest-lived 15 male and female Rufous-and-white Wrens in this dataset, I analyzed two aspects of song ontogeny: spectro-temporal variation and variation in repertoire use over each birds’ adult lifetime. My results reveal that most of the variation in wren song was not explained by differences in age, although there were a few variables that did vary with the age of the singer: pause lengths in the introductory portion of the song decreased with age for both sexes, and frequency of the song’s terminal note increased with age for females. I also note that female songs were sung at higher frequencies and wider bandwidths than male’s songs. I discuss the implications of my findings and I highlight directions of future research in this field with specific predictions for how age-related changes in crystallized song might function in birds.