Bird species diversity in riparian buffers, row crop fields, and grazed pastures of two agriculturally
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A design goal associated with most riparian buffer systems is the enhancement of wildlife habitat. To determine whether this goal was being met, we compared breeding bird composition at five sites, including riparian buffers, nearby row crop fields, and an intensively grazed pasture along Bear Creek and Long Dick Creek in north-central Iowa, USA. The riparian buffers consisted of native grasses, forbs, and woody vegetation and represented three different ages (14+, 9, and 2 years old). At each site, 10 min point counts for breeding birds were conducted using 50 m fixed radius plots, which were visited eight times between May 15 and July 10, 2008. A total of 54 bird species were observed over all of the study sites. The installed riparian buffers incorporated in this study had higher bird abundance, richness, and diversity than the crop and pasture sites. The fewest species were detected within row crop fields (15 species) while the most species were observed on the oldest riparian buffer (42 species); intermediate numbers were observed on the 9 year-old (27 species) and 2 year-old (28 species) buffers and the pasture (23 species). Our results suggest that re-establishing native riparian vegetation in areas of intensive agriculture will provide habitat to a broader suite of bird species. In comparison to row crop and grazing land, the buffers contain a greater diversity of vegetative structure in both horizontal and vertical dimensions. Many birds are known to respond positively to such habitat heterogeneity.