Grasslands throughout the United States have been lost at incredible rates, and most grassland obligate bird species also have experienced significant downward trends. While the reasons for these declines are many, habitat loss has played a substantial role. Grasslands in Pennsylvania, created through coal surface-mining reclamation activities, provide an important habitat for grassland birds: notably Grasshopper (Ammodramus savannarum) and Henslow’s Sparrows (A. henslowii). These reclaimed grasslands, however, are being lost to successional processes as woody plant species recolonize these areas. Grassland sparrow abundance and fitness are thought to decline with increasing woody vegetation; although this evidence is based on observation and correlation and has largely been measured in grasslands with little woody vegetation.
With these ideas in mind I implemented a large-scale manipulative experiment in the spring of 2009 to measure the influence of woody vegetation on the abundance and fitness of grassland birds. After collecting avian baseline and vegetation data on eight 50-ac plots during 2009, we will remove all woody vegetation from half of those plots during the winter of 2010. By monitoring these plots for the following two years, I will be able to link habitat structure and composition with territory shifts, return rates, nestling growth rate, survival, and changes in population size. Finally, I will conduct multiple grassland bird surveys at hundreds of grassland sites across western Pennsylvania. I will model occupancy rates and develop a population estimate for grassland sparrows in western Pennsylvania. Taking what we learn from the woody vegetation removal experiment, I will be able to estimate the percent of grasslands in western Pennsylvania that contain viable populations of grassland birds.