Predicting avian population trends in high intensity agroecoregions

Background/Question/Methods

Human demand for land and resources has altered ecosystem structure and function.  Consequently, the rate of biodiversity loss is well beyond planetary thresholds. The central Great Plains of North America represents one of the most altered, though agriculturally productive, regions of the world. Biomass production in the region has doubled over the last 40 years. The ultimate implications of the observed rapid change largely remain unknown, and interests in closing the yield gap and increasing biofuel production highlight the need to know what is expected to happen with future increased intensification. In particular, new models are needed to predict the response of biodiversity to land use change and agricultural intensification in the Great Plains.

Using bio-economic data from 100 counties in along the 41st parallel through the central Great Plains, we modeled avian populations and communities with covariates of agricultural intensification. We used forty years of counts from the North American USGS Breeding Bird Survey as the response variable. Intensification covariates were derived from measures of biomass production and input use over the same spatial and temporal scale. We used generalized linear mixed models and AIC model selection to test competing models.

Results/Conclusions

The best model for all measures of bird diversity and abundance was the global model. However, wide confidence intervals limited inference for both species richness and total abundance. Analysis of regional grassland species of conservation concern (e.g., Western Meadowlark, Grasshopper Sparrow, and Dickcissel) suggested a relationship between chemical use and abundance, with abundance of these species declining as chemical use increased. Future analysis will consider additional species and measures of community diversity.

Applied conservation efforts aimed at stabilizing or reversing the loss of biodiversity, in particular grassland bird populations, have largely focused on protected areas and local remnant or restored natural areas. Despite significant advances in our understanding of the ecology of these systems, effective conservation actions continue to be elusive. These data suggest that the intensification of farmland may limit the benefits of conservation investments in protected and restored patches. These results are consistent with data on farmland birds in Europe, where declines in bird diversity have been attributed broadly to agricultural intensification. Ultimately, biodiversity conservation practitioners need solutions that integrate traditional conservation efforts with the demand for increased biomass production.