Narrowness of habitat selection in woodland and grassland birds

Abstract

Conservationists have long been concerned about population declines among both woodland and grassland birds, especially those that require extensive areas of a preferred habitat type and avoid mixed habitats. Of the two groups, grassland species have declined even more rapidly than woodland species. We examined whether requirements for uninterrupted habitat could contribute to the greater population declines among grassland birds. To do this, we plotted frequency of occurrence in relation to tree cover in the landscape to evaluate narrowness of range in habitat selection, or stenotopicity, for woodland and grassland species. We created plots at three scales of 200 m, 400 m, and 1200 m around bird observations. At all scales, the most stenotopic woodland species had thresholds of occurrence of 10-30% tree cover. In contrast, most grassland species had thresholds of 80-90% grassland. Favored ranges of grassland species were also narrower than those of woodland species. Grassland species thus are dramatically more stenotopic than woodland species. Although habitat loss is a serious consideration for both groups, grassland birds face a double vulnerability, with high sensitivity to habitat extent as well as extreme habitat loss. This study highlights the importance of increasing systematic strategies to conserve grassland habitat at the regional scale.

Keywords

• area sensitivity
• grassland birds
• habitat fragmentation
• loess
• stenotopicity
• woodland birds