BirdsAmong many passerine species, repertoire size for a given adult male is thought to directly impact fitness as a result of myriad evolutionary pressures. Recent evidence suggests, however, that the percentage of songs shared within a given males repertoire, regardless of repertoire size, may actually be responsible for the increased fitness previously thought to be influenced by repertoire size alone. Highly shared songs similar in two distant geographic regions may also function for conspecific recognition beyond mate attraction. I observed song sharing for a population of American Restarts (Setophaga ruticilla) located on Grapevine Point (GVP), one mile northeast of the University of Michigan Biological Station in Pellston, MI. By indentifying eight distinct song types on GVP, I documented the rate of songs shared and repertoire size for five male American Redstarts. Mean repertoire size for adult males on GVP did not differ significantly from the same mean calculated for American Redstart populations located in New Brunswick, Canada (Lemon et al. 1985). Song Type 1 was the most highly shared song on GVP and was very similar to the most shared song type (Song Type 1) in New Brunswick. These similarities support the hypothesis that highly shared song types of one population will also be highly shared among other populations. Although the specific function of these highly shared songs is unknown, evidence from other Passeriformes suggests that a high degree of song sharing implies a positive effect on individual territory tenure and subsequent fitness.http://deepblue.lib.umich.edu/bitstream/2027.42/64851/1/White_Alexander_2009.pd
