title: Impacts of tree rows on grassland birds and potential nest predators: a removal experiment.
abstract: Globally, grasslands and the wildlife that inhabit them are widely imperiled. Encroachment by shrubs and trees has widely impacted grasslands in the past 150 years. In North America, most grassland birds avoid nesting near woody vegetation. Because woody vegetation fragments grasslands and potential nest predator diversity and abundance is often greater along wooded edge and grassland transitions, we measured the impacts of removing rows of trees and shrubs that intersected grasslands on potential nest predators and the three most abundant grassland bird species (Henslow's sparrow [Ammodramus henslowii], Eastern meadowlark [Sturnella magna], and bobolink [Dolichonyx oryzivorus]) at sites in Wisconsin, U.S.A. We monitored 3 control and 3 treatment sites, for 1 yr prior to and 3 yr after tree row removal at the treatment sites. Grassland bird densities increased (2-4 times for bobolink and Henslow's sparrow) and nesting densities increased (all 3 species) in the removal areas compared to control areas. After removals, Henslow's sparrows nested within ≤50 m of the treatment area, where they did not occur when tree rows were present. Most dramatically, activity by woodland-associated predators nearly ceased (nine-fold decrease for raccoon [Procyon lotor]) at the removals and grassland predators increased (up to 27 times activity for thirteen-lined ground squirrel [Ictidomys tridecemlineatus]). Nest success did not increase, likely reflecting the increase in grassland predators. However, more nests were attempted by all 3 species (175 versus 116) and the number of successful nests for bobolinks and Henslow's sparrows increased. Because of gains in habitat, increased use by birds, greater production of young, and the effective removal of woodland-associated predators, tree row removal, where appropriate based on the predator community, can be a beneficial management action for conserving grassland birds and improving fragmented and degraded grassland ecosystems.
authors.affiliation: Department of Forest and Wildlife Ecology, University of Wisconsin, Madison, Wisconsin, United States of America. kellison@wcs.org
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Ellison
authors.forename: Christine A
authors.initials: CA
authors.lastname: Ribic
authors.forename: David W
authors.initials: DW
authors.lastname: Sample
authors.forename: Megan J
authors.initials: MJ
authors.lastname: Fawcett
authors.forename: John D
authors.initials: JD
authors.lastname: Dadisman
mesh_terms: D000818:Animals; D001717:Birds; D017753:Ecosystem; D005260:Female; D008297:Male; D009425:Nesting Behavior; D006109:Poaceae; D011156:Population Density; D011235:Predatory Behavior; D014197:Trees; D014922:Wisconsin
references.citation: Oecologia. 2007 Dec;154(3):493-503
references.pmid: 17924149
references.citation: Trends Ecol Evol. 2008 Feb;23(2):104-12
references.pmid: 18191278
references.citation: J Anim Ecol. 2006 Mar;75(2):340-9
references.pmid: 16637987
references.citation: Ecol Appl. 2008 Jun;18(4):928-44
references.pmid: 18536253
references.citation: J Anim Ecol. 2008 Mar;77(2):370-7
references.pmid: 18028357
references.citation: Conserv Biol. 2009 Jun;23(3):588-98
references.pmid: 19183203