The greater prairie-chicken is a mid–sized grouse widely known for its male display behavior during mating season.  It is found in open prairie, grassland, and oak savannahs ranging from Texas into Illinois and South Dakota.  Conversion of North American grasslands into agriculture during the 20th century has dramatically decreased prairie-chicken populations, leading to recent management and conservation efforts.  While rising cropland coverage has eliminated available nesting sites, it has also provided birds with novel foraging opportunities.  The diet of the prairie-chicken consists of leaves, seeds, grains, and insects in variable proportions depending upon relative availability and season.  To analyze the relative proportion of vegetation versus insects in the diet of these populations, we analyzed wing feathers collected from two regions of Nebraska for nitrogen and carbon stable isotope analysis. As part of a larger study, these birds were collected from two regions of Nebraska: North Central (Cherry, Brown, Rock, Holt, Loup, Wheeler, Custer and Greeley counties) and Southeast (Otoe, Gage, Johnson, and Pawnee counties).  Land use varies between these regions, with the Southeast consisting of 41% grassland and 49% cropland (31% corn, 69% other) compared to the North Central with 80% grassland and 14% cropland (54% corn, 46% other).
Results/Conclusions

Birds collected in the North Central region exhibited lower δ15N (3.583 ‰, n=24) compared to birds from the Southeast region (5.058 ‰, n=19, p=0.0006).  North Central birds also had a more positive δ13C values compared to Southeast birds (-21.530 compared to -22.364‰, p=0.0278).  Increases in δ15N values suggest a shift in diet associated with land coverage.  North Central Nebraska has a much larger area of grasslands compared to the Southeast and it is possible native seeds and other vegetative material dominates the diet of these birds.  In contrast, birds from the Southeast may be switching away from native seeds and feeding predominantly on insects.  The isotopic information is consistent with this scenario; prairie chickens originating from the Southeast express a nitrogen isotopic value suggestive of feeding at a higher trophic level. The variation in carbon isotopic values of feather between the two populations is likely the result of corn in the birds’ diet.  Corn is a C₄ plant and expresses a less negative carbon isotopic value compared to C₃ plants.  The North Central region of Nebraska has significant corn production and consumption of this grain by prairie-chickens may be responsible for the more positive δ13C feather value.