• Rocky Mountain Research Station
• 240 West Prospect
• Fort Collins, CO 80526
• (970) 498-1100

Impacts of Invasive Plants on Songbirds: Using Song Structure as an Indicator of Habitat Quality

Using understandings derived from our long-term research of spotted knapweed, we are testing a novel method for assessing songbird population status and habitat quality that is based on an easily measured parameter: song structure. Song structure refers to the array of song types sung by a species in a particular area, and song types vary over space much like accents do in humans. Young birds acquire their one signature song with its particular accent by learning from their neighbors in their first breeding year. Areas with high habitat quality should have low turnover of breeding adults between years and therefore be dominated by older birds who learned their song on the site and sing in the local accent, readily passing down the song tradition to younger birds. In contrast, areas with low habitat quality should have relatively few older birds to serve as teachers and their songs should exhibit greater variety since they were likely acquired in other places. These differences should affect song structure, as young birds settling in high-quality sites readily learn the local accent from their older neighbors, maintaining the song tradition when they return in subsequent breeding seasons, while those settling in low quality habitats learn a mix of songs from various neighbors only to disperse in future seasons.

We are using two years of field data to link changes in habitat quality caused by spotted knapweed invasion to differences in song structure at invaded compared to native-dominated sites. Songs of >200 individually marked Chipping Sparrows were recorded at 7 sites on the Lolo National Forest in western Montana. Preliminary analyses support the idea that song structure may be a important indicator of habitat quality: songs at native-dominated sites formed cohesive neighborhoods that were more similar to each other than those at knapweed-invaded sites. Sampling at additional sites over a range of habitats will be necessary to evaluate song structure as a broadly applicable measure of population status. Given the links between song learning, turnover rates, and habitat quality in songbirds, song structure may serve as a new and greatly improved means of monitoring population status, including the impacts of invasive species.

References

Ortega YK, and DE Pearson. 2005. Strong versus weak invaders of natural plant communities: assessing invasibility and impact. Ecological Applications 15(2):651-661.