DISSERTATION RESEARCH: Effects of Habitat Heterogeneity on Songbird Fecundity in an Experimental Landscape

Kansas State University, Manhattan KS

Investigators

Abstract

Landscape heterogeneity promotes higher biodiversity in natural ecosystems. In North America, tallgrass prairie was historically maintained as a mosaic of different habitats by the interaction between fire and selective grazing by large herbivores, including bison, elk and pronghorn. In recent decades, agricultural intensification has led to more homogeneous landscapes in managed grasslands, which has been linked to widespread declines in songbird populations in North America and Europe. A loss of heterogeneity in grasslands could have major consequences for birds by changing food availability, predation risk, or rates of brood parasitism by Brown-headed Cowbirds (Molothrus ater). The proposed field study will estimate the effects of habitat heterogeneity on movements and survival of juvenile Dickcissels (Spiza americana), a songbird of conservation concern. The project will provide a better understanding of the reproductive ecology of grassland songbirds in managed grasslands, and will aid in understanding the relationships among grassland management and ecology, bird populations, and conservation. This field study will be conducted in the Flint Hills ecoregion of eastern Kansas and Oklahoma, where large tracts of native tallgrass prairie still remain, however habitat quality has been impacted by ongoing changes in rangeland management. Konza Prairie is an NSF-funded Long-term Ecological Research (LTER) site in the northern Flint Hills, and provides a unique experimental landscape with different levels of habitat heterogeneity created by long-term grazing and fire treatments. Patch-burn grazing management increases heterogeneity in vegetative structure because only a third of the pasture is burned each year in a three-year rotational scheme, and movements of grazing cattle are unrestricted. A fourth pasture with annual burns and season-long stocking of cattle will be a negative control, and a fifth pasture with annual burns but no grazing will be a positive control. The researchers will attach small radio-transmitters to a total of 60 fledglings, across the five experimental treatments. Fledglings will be re-located daily during the first 30 days after leaving the nest to determine movements and survival. The research will estimate fledgling movements, arthropod prey availability, and fledgling survival using field methods and statistical analyses. Understanding how biotic factors interact with demographic parameters like nest and fledgling survival will help to understand the role of landscape heterogeneity on the life-history strategies of birds.