Document: THO-3-52-10

The role of small mammal predation on nesting success of grassland nesting birds.

STANLEY, T.R.*

U.S. Geological Survey, Fort Collins, Colorado 80525 USA ¹

Abstract:
Birds endemic to the central shortgrass prairie ecoregion have experienced steep and widespread declines in the past three decades. While the causes for these declines have not been identified, factors influencing reproductive success have been implicated. Nest predation is the major cause of nest failure in passerines and nesting success of prairie birds in the shortgrass prairie is exceptionally low. Data collected in 1997 on the Pawnee National Grasslands, Colorado, suggested nest predation on grassland birds was higher in fragmented tracts of shortgrass prairie, where the vegetation is taller in stature, than in the shorter vegetation associated with unfragmented landscapes. One possible explanation for this pattern is that the increased vegetative structure on fragmented and other altered landscapes; for example prairie sites put into the Conservation Reserve Program (CRP), supports denser populations of small mammals, the primary nest predators of ground-nesting grassland birds. In this study, I compared vegetation structure, small mammal densities, and artificial nest predation rates on fragmented shortgrass prairie sites and CRP sites, with unfragmented (intact) shortgrass prairie sites. In 1998 eight intact and eight fragmented shortgrass prairie sites were paired and sampled, and in 1999 seven intact and seven CRP sites were paired and sampled. Small mammal densities were estimated using trapping webs, and nest predation rates were estimated using artificial nests containing one Japanese quail egg and, optionally, one clay egg. Vegetation structure on fragmented shortgrass prairie and CRP sites differed from intact shortgrass prairie sites, but vegetation structure was not found to be a good predictor of small mammal densities. On paired intact and fragmented shortgrass prairie sites small mammal density was found to be the best predictor of nest predation rates, whereas on paired intact and CRP sites vegetation structure was found to be the best predictor of nest predation rates. Small mammal species composition was similar on paired intact and fragmented shortgrass prairie sites, whereas it differed markedly on paired intact and CRP sites.

Keywords: small mammals, predation, nesting success, grassland birds, shortgrass prairie, landscape fragmentation, CRP

This abstract is being presented at: 10:30 AM in session:
Oral Session #3: Avian Ecology.