Although plant invaders are known for their negative effects on natural systems, the extent of these impacts is often unknown. We studied how invasion of spotted knapweed (Centaurea stoebe) into grasslands of western Montana impacted native species from plants to insects to birds. Native plants declined with increasing levels of invasion, as did important insect groups that provide food for ground-foraging songbirds such as chipping sparrows. Chipping sparrows breeding in knapweed-invaded habitat produced fewer young and had lower site faithfulness compared to birds in habitat dominated by native vegetation. As a result, the prevalence of yearling versus older adults was twice as high in invaded compared to native habitat, a shift that affected the way song was passed between generations.
Before they breed for the first time, chipping sparrows adopt a signature song kept for life. Yearlings in our study did so primarily by matching the songs of older birds rather than introducing new ones. Therefore, in invaded habitat where there were relatively few older birds to serve as teachers, the number of song types was reduced by nearly 20 percent, mirroring the loss of native plant and insect resources. Song diversity may provide a novel way to assess the sensitivity of birds to habitat change.
Related Documents and Media:
University of Wisconsin, Conservation Magazine. Invasive plant reduces number of bird songs. August 30, 2013.
McQuillan, K. Montana Public Radio. How spotted knapweed affects birdsong. September18, 2013.