100 Years of Changing Bird Populations in Illinois Jeffery W. Walk, The Nature Conservancy, Michael P. Ward and Steven D. Bailey, Illinois Natural History Survey, and Jeffrey D. Brawn, University of Illinois at Urbana-Champaign Study Sites Replicating Historic Surveys Results The locations surveyed 100 years ago are vaguely known. Gross and Ray typically took trains to starting points, and walked for several days to another railroad, counting and collecting birds along the way, sleeping in hotels, barns or homes when they were invited. In the 1950 s, the Graber’s surveyed from 96 locations (described with varying precision), split evenly among northern, central, and southern Illinois. We originated our surveys from each of these 96 areas, sampling all land cover types within about 3 miles of that point. From 1906 -1909, Alfred Gross & Harold Ray (right), directed by (right), Stephen Forbes, sampled birds in various habitats throughout Illinois. These surveys were the first quantitative descriptions of the bird communities within various land cover types. Richard and Jean Graber used the same methods to measure avian diversity and abundance in habitat types in northern, central and southern Illinois. Their work from 1956 -1958 examined changes over the preceding 50 years, and estimated statewide populations for several common species. We repeated these surveys from 2006 -2008, and are comparing distribution, abundance and richness of bird species to results from 50 and 100 years ago. The hand-held computers used for entering bird data in ‘real time’ during transects and point-counts include a GPS receiver that logged our location every 5 seconds. Sampling Effort, By the Numbers: Changes in land cover/land use have been dramatic over the past century. Corn has consistently been the dominant land use, with soybeans becoming important after about 1930. Forested areas have expanded steadily since 1920. Land Cover of Illinois, 1900 -2000 Small grains, hay, and pasture (collectively), have been reduced from 50% of the state’s area in 1900, to about 7% in 2000. Bird communities within some habitats have changed profoundly, particularly grasslands. Meadowlarks, dickcissels, bobolinks, and grasshopper sparrows (“grasslanders, ” below, left) were 40% of the birds found in grasslands in the 1900 s, 35% in the 1950 s, and 13% at present. In contrast, forest bird communities have been relatively stable (below, right). Birds Encountered in Grasslands Birds Encountered in Forests 20, 164 individual birds Of 132 species Recorded on 963 transects Totaling 54, 743 meters Representing 23 habitat types. Methods Forbes was an aquatic entomologist, and apparently regarded sampling birds in the field similarly to sampling bugs in a stream. He described the method he devised as: “…a gigantic sweep-net, 150 feet wide and 300 feet deep, so drawn across the country day by day as to capture every bird which comes in its way …” Two observers walk in parallel lines, often for miles, recording birds seen between and up to 300 feet in front of them. Because more birds are heard, but not seen, as vegetation height and density increase, the Graber’s dryly noted: “…the strip census is not well adapted to woodland areas. ” “…the To supplement the unusual transect method, and to account for birds heard but not seen, we conducted paired-observer, 5 -minute point-counts with distance estimation. These results will be more comparable with other contemporary surveys, such as the North American Breeding Bird Survey. Winners… Birds of suburbs and forest edges, water birds (herons, geese, gulls) …and Losers Grassland, shrubland, savanna, and marsh birds Funding for this study is from the State Wildlife Grants Program, project T-16 -P-1. Special thanks to hundreds of landowners! Other Interesting Notes… The Rich Keep Getting Richer, the Poor Keep Getting Poorer: Just 5 abundant generalists – red-winged blackbird, European starling, common grackle, American robin, house sparrow –made up 55% of all birds recorded. More than 40 species, present in small numbers the 1900 s and 1950 s, went undetected. Southern Birds Expand Northward: Red-bellied woodpeckers, Carolina wrens, northern cardinals, and tufted titmice occur farther north at great abundance than 100 years ago. Are land use, practices such as birdfeeding, or climate change behind these shifts? “New” to the Survey: Absent in the 1900 s or 1950 s, but again nesting in Illinois, are sandhill cranes, bald eagles, Canada geese, and wild turkeys. House finches and Eurasian collared-doves are recently-introduced birds, now found statewide.
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