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Title: Habitat availability is a more plausible explanation than insecticide acute toxicity for U.S. grassland bird species declines

Author
item HILL, JASON - Pennsylvania State University
item Egan Jr, John
item STAUFFER, GLENN - Pennsylvania State University
item DIEFENBACH, DUANE - Us Geological Survey (USGS)

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2014
Publication Date: 5/20/2014
Citation: Hill, J., Egan Jr, J.F., Stauffer, G., Diefenbach, D. 2014. Habitat availability is a more plausible explanation than insecticide acute toxicity for U.S. grassland bird species declines. PLoS One. 9(5):e98064. doi:10.1371/journal.pone.0098064.

Interpretive Summary: Grassland birds are an important feature of farm ecosystems and contribute to biological pest control and the cultural and aesthetic value of rural landscapes. Unfortunately, they are also the most rapidly declining group of bird species in North America. Previously, grassland bird declines were thought to be primarily caused by the loss of key farmland habitats such as permanent pasture, remnant natural grasslands, and Conservation Reserve Program (CRP) areas. Recently, however, a well-publicized paper identified exposure to toxic insecticides as a more important factor explaining grassland bird decline than habitat availability. We re-analyzed the data presented in that paper and also explored a similar data set to re-evaluate whether insecticide exposure or habitat availability is more important in explaining grassland bird declines. We found that bird declines are very clearly linked to habitat availability but found no support for insecticide exposure as a factor. Fostering farming landscapes that include habitats like pasture, rangeland, and CRP may offer the best hope for reversing grassland bird declines.

Technical Abstract: Grassland bird species have experienced substantial declines in North America. These declines have been largely attributed to habitat loss and degradation, especially from agricultural practices and intensification (the habitat-availability hypothesis). A recent analysis of North American Breeding Bird Survey (BBS) “grassland breeding” bird trends reported that insecticide acute toxicity was a better correlate of grassland bird declines in North America from 1980 – 2003 (the insecticide-acute-toxicity hypothesis). We reexamined and expanded upon this recent research supporting the insecticide-acute-toxicity hypothesis, because it is important to correctly identify the most likely causes of grassland bird declines so that research efforts are focused on the most likely hypotheses and limited conservation funding can be used most effectively. Using the same BBS data, we rejected the insecticide-acute-toxicity hypothesis because we found stronger correlations with covariates that supported the habitat-availability hypothesis. We found grassland bird trends were positively associated with increases in acreage of cropland used as pasture, Conservation Reserve Program (CRP) lands, and collectively all non-intensively-managed grasslands. Models representing the habitat-availability hypothesis were 4–21 times better supported than models representing the insecticide-acute-toxicity hypothesis. Our findings suggest that grassland bird populations will benefit from multifunctional landscapes where crop fields are interspersed with pastures, CRP lands, rangelands and other grassland habitats.