Using birds as indicators of biodiversity status for two North Dakota counties

Background/Question/Methods Biodiversity in the Northern Great Plains is threatened by the long history of conversion of prairie grasslands to agriculture and other uses. Biodiversity may be assessed using indicator species such as birds. This study used an assemblage of 11 birds to develop an overall index of biodiversity status for two counties in North Dakota with contrasting land use. Grand Forks County is one of the more heavily populated counties in North Dakota and has a large amount of cultivated land. Stutsman County, North Dakota, sits on the edge of the prairie pothole region and is only lightly populated. Habitat suitability maps were developed for each of the 11 bird species using GAP land cover data, presence/absence observations, and detailed literature survey of individual bird species behavior. Patch size and threat proximity factors were incorporated using Fragstats to create detailed maps defining patch structure at 1/16 section scale (about 1600 m²) to match land management units. A habitat suitability attribute table was linked to the fragmentation maps for each of the 11 bird species, which were then used in InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) to create biodiversity index maps from different weightings of individual bird indicators.

Results/Conclusions The biodiversity index was based on summing individual bird habitat suitability indicators and rescaling the total between zero and 100. When the biodiversity index was based on even weighting of individual bird indicators, average values for Grand Forks County were 61 for grassland, 32 for cropland, and 17 for developed land. The average values for Stutsman County were 57 for grassland, 31 for cropland, and 11 for developed. When three species with positive associations with croplands and developed areas were not included in the combination, index values on cropland and developed land decreased for both counties. Wetland analysis was undertaken separately at a finer scale, and results were incorporated into the final index by merging grids. Overlays for wetlands based on two obligate wetland bird species alone, produced a mean biodiversity index for wetlands of 58 for Grand Forks County and 68 for Stutsman County. These results indicate that birds can be used to develop a useful biodiversity index, but that index values are highly sensitive to the way individual indicators are combined, the resolution of the analysis and scaling of features, and the quality of the data that relates bird behavior to habitat.