Habitat fragmentation effects on birds in grasslands: A critique of our knowledge

Habitat fragmentation exacerbates problems due to habitat loss for grassland and wetland birds. Remaining patches of grassland and wetland may be too small, too isolated, and too influenced by edge effects to maintain viable populations of some breeding birds. Knowledge of the effects of fragmentation on bird populations is critically important for decisions about reserve design, grassland and wetland management, and implementation of cropland set-aside programs that benefit wildlife. In this article I review research that has been conducted on habitat fragmentation, and note common problems in the methodology used. The results of many studies are compromised by use of methods that are now recognized as inappropriate. As expected, some large-bodied birds with large territorial requirements, such as the northern harrier are area-sensitive. In addition, multiple studies have shown that some small species of grassland birds favor patches of habitat far in excess of their territory size. Among these species are the Savannah, grasshopper, and Henslow's sparrows and the bobolink. Single studies or studies that employed less-reliable methods have suggested other species may be area-sensitive as well. The literature on area-sensitivity among wetland birds includes virtually no studies based on solid methodologies. Distinguishing supportable conclusions from those that may be artefactual is important when practical decisions are made.