Date of Award


Publication Type

Master Thesis

Degree Name



Biological Sciences


call; migration; Nocturnal flight calls; songbird; warbler


Mennill, Dan


Foote, Jenn




The nocturnal flight calls of birds are short vocalizations, produced primarily during migration. Although these calls offer a unique opportunity for studying avian migration, there has been little research into many aspects of these calls, such as the species-specificity of the calls of closely related taxa, or variation in calls associated with age, sex, or geography. The objective of my thesis research was to investigate acoustic variation within the flight calls of songbirds to expand our understanding of these calls and their application in migration monitoring. I recorded the flight calls of birds held for banding as well as birds actively flying during their nocturnal movements. In my first data chapter, I investigated whether the nocturnal flight calls of nine warbler species (i.e. the “zeep” species-group) exhibited acoustic differences. Analysis of the acoustic properties of flight calls of these species revealed significant differences in call structure between species, including five species that were notably different from the others in one or more acoustic properties. My results revealed that flight calls could be assigned to the correct species more often (73%) than expected by chance (36%), although the classification was not perfect. Therefore, acoustic variation in the flight calls of the “zeep” complex can be used to identify more species than previously thought. In my second data chapter, I explored intraspecific variation in flight calls. I found no evidence of sex-based or age-based variation in three species, and no evidence of geographic variation in two species. Although I found geographic variation in the calls of Dark-eyed Juncos, there was no consistent pattern on an east-west axis. Together, these results provided very little evidence for variation in flight calls with sex or age and limited evidence for geographic variation. Consequently, flight calls may be used to identify species (or species-groups) but not to identify sex, age, or geographic origin. My research serves to enhance the capabilities of nocturnal flight call detections for monitoring migratory birds while improving our understanding of drivers of variation in these calls.