Tuesday, March 4, 2014

abstract of a new paper published in the journal Ecology - the effects of exotic plants on a songbird

Invasive plant erodes local song diversity in a migratory passerine

 Ecology, 95(2), 2014, pp. 458–465
  by the Ecological Society of America

1Rocky Mountain Research Station, USDA Forest Service, 800 East Beckwith Avenue, Missoula, Montana 59801 USA
2College of Forestry and Conservation, Wildlife Biology Program, University of Montana, Missoula, Montana 59812 USA
3Division of Biological Sciences, University of Montana, Missoula, Montana 59812 USA

Abstract. Exotic plant invasions threaten ecosystems globally, but we still know little
about the specific consequences for animals. Invasive plants can alter the quality of breeding
habitat for songbirds, thereby impacting important demographic traits such as dispersal,
philopatry, and age structure. These demographic effects may in turn alter song-learning
conditions to affect song structure and diversity. We studied Chipping Sparrows (Spizella
passerina) breeding in six savannas that were either dominated by native vegetation or invaded
by spotted knapweed (Centaurea stoebe), an exotic forb known to diminish food resources and
reproductive success. Here, we report that the prevalence of older birds was relatively low in
knapweed-invaded habitat, where recruitment of yearlings compensated for diminished site
fidelity to sustain territory abundance. In both habitat types, yearling males tended to adopt
songs similar to their neighbors and match the songs of older birds rather than introducing
new song types, a pattern seen in many songbird species. As a consequence, in invaded habitat
where age structure was skewed away from older birds serving as potential song models,
yearlings converged on fewer song types. Similarity of songs among individuals was
significantly higher and the overall number of song types averaged nearly 20% lower in
invaded relative to native habitat. Degradation of habitat quality generally impacts site fidelity
and age ratios in migratory songbirds and hence may commonly alter song-learning
conditions. Associated shifts in song attributes known to influence reproductive success could
in turn enforce demographic declines driven by habitat degradation. Local song structure may
serve as an important indicator of habitat quality and population status for songbirds.

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