Habitat Fragmentation Study

Study Title

Predation on nests of grassland birds in the U.S. Prairie Pothole Region: predator foraging behavior, predation patterns, and nesting success

Collaborators

The project is a joint effort among Bill Clark (Coordinator), Rolf Koford, Marsha Sovada, and Ray Greenwood. Drs. Clark and Koford are in the Department of Animal Ecology at Iowa State University. Koford is also in the Iowa Cooperative Fish and Wildlife Research Unit. Dr. Sovada and Mr. Greenwood are with the Northern Prairie Wildlife Research Center. Two Ph.D. students, Mike Phillips and David Horn, are focusing on predator movements and foraging and on nest success of grassland birds, respectively. This is a project of Ducks Unlimited's Institute for Wetland and Waterfowl Research (IWWR) and the collaborators are grateful for their generous support.

Study Overview

We are examining both the foraging behavior of major predators on nests of grassland birds and the nesting success of grassland birds on study areas in North Dakota. We are analyzing relations between predators and prey to develop recommendations for managers and policy makers concerned with declining populations of grassland birds. The study is being funded by the Institute for Wetland and Waterfowl Research, the research arm of Ducks Unlimited, and by the Northern Prairie Wildlife Research Center, a research laboratory of the Biological Resources Division of the U.S. Geological Survey.

Contact information

William Clark

Telephone: 515-294-5176; Fax: 515-294-7874; E-mail: wrclark@iastate.edu

Rolf Koford

Telephone: 515-294-3057 or 294-3056; Fax: 515-294-5468; E-mail: rkoford@iastate.edu

Marsha Sovada

Telephone: 701-252-5363; E-mail: Marsha_Sovada@nbs.gov

Raymond Greenwood

Telephone: 701-252-5363; E-mail: Ray_Greenwood@nbs.gov

Study Outline

Background

Ecosystem and landscape management should be based on a firm understanding of the biological processes responsible for observed patterns. In the highly fragmented agricultural landscape of the northern Great Plains, nesting success of grassland birds is often too low to sustain stable populations. There are theoretical reasons to suspect that habitat fragmentation contributes to low nesting success, but empirical studies of this relationship are rare for grassland species.

Edge effects on nesting success have been documented in one Minnesota study of grassland passerines. Two of the collaborating biologists in this proposal (Greenwood and Sovada) are conducting studies of grassland-patch size on nesting success of upland-nesting ducks while simultaneously collecting data on predator abundance. The key missing information in these studies concerns the process that links habitat pattern and nesting success, that is, foraging behavior of predators.

Movement and foraging patterns of predators in fragmented landscapes are poorly known and have not been studied adequately while simultaneously examining nesting success. Our goal is to investigate these patterns and develop management recommendations that take advantage of knowledge of predator behavior.

Team

We have taken a collaborative approach to conducting this research, recognizing that the required research will benefit from multiple perspectives and funding sources. Two Ph.D. students round out our team of four investigators, each of whom has many years of experience with predators, nesting success of grassland birds, or both.

Study Areas

The study areas are in North Dakota to take advantage of the diversity of nesting, grassland birds and to facilitate logistics. We radio-track striped skunks and red foxes and monitor nesting success of grassland birds (mostly ducks) on the same areas.

Study Design

The proposed design examines predator-prey interactions in two regions of the habitat- fragmentation continuum, expressed as the percentage of a local landscape composed of grassland. These regions were selected to be as far apart as possible (maximizing potential for differences in important variables) while still being within the range that might be practically managed. One region of the continuum is a landscape composed of 30-50% grassland. Previous experience in North Dakota indicates that, with this level of fragmentation, the grassland is continuous or nearly continuous. The other region is a landscape with 5-10% grassland, where many patches of grassland habitat are far apart or connected by narrow corridors.

Each year of the study, we will select study areas in these two regions, called Continuous and Fragmented. Our primary aim is not to test the effect of degree of fragmentation on nesting success; this has been tested previously and findings are often confounded by geographic clines in nesting success. Rather, we seek to understand the mechanisms and processes underlying differences in nesting success.

Hypotheses

We are testing the following six hypotheses:

Nesting success will be less variable in the Fragmented landscape, due to the reduced spatial diversity of the landscape.
The predator community in Continuous grasslands will be dominated by, among the canids, coyotes, whereas the Fragmented grasslands will be dominated by red foxes and generalist, edge-oriented predators, such as striped skunks.
Predator occurrence will be correlated with the intensity of human use of the landscape.
Foraging in a given area of any patch of perennial grassland habitat will be more concentrated in the Fragmented grassland than in the Continuous grassland.
Skunks will forage more frequently in landscape areas that include edges and other landscape corridors than in areas away from edges, whereas foxes will forage as frequently in areas away from edges as in those including edges.
Nest success will be correlated with predator foraging intensity, in relation to patch size and isolation, and with location in patches (i.e., edge versus interior).

A final objective, not stated as a testable hypothesis, is to use our observations to apply foraging theory models.

Progress

Two years of field work have been completed and analysis of data is progressing. Mike Phillips and David Horn presented seminars at Oak Hammock Marsh, Manitoba, at the biennnial staff/student workshop sponsored by IWWR. David Horn and Rolf Koford presented a poster at the annual conference of The Wildlife Society in September, 1997. The Unit's most recent annual report contained a short progress report.

Updated 11 November, 1997.

rkoford@iastate.edu

URL: http://www.public.iastate.edu/~rkoford/fragstud.htm