Bobolink Dispersal Patterns And Metapopulation Persistence
Daniel M. Scheiman, Department of Forestry and Natural Resources, 195 Marsteller St., Purdue University, West Lafayette, IN 47907; (765) 496-2845; FAX (765) 496-2422; scheiman@purdue.edu
John B. Dunning Jr., Department of Forestry and Natural Resources, 195 Marsteller St., Purdue University, West Lafayette, IN 47907
Land management in the agriculture-dominated Midwest has changed the quantity and quality of grassland habitats. This has led to concomitant declines in grassland-dependent birds, and subdivision of populations. The metapopulation model is often used to describe spatially subdivided populations. Dispersal is a key element in metapopulation models. Local and landscape-level factors influence dispersal rate, which in turn influences metapopulation size and persistence. Grassland bird populations occupying a fragmented landscape may behave as a metapopulation, but dispersal rates, and hence population persistence probabilities, are largely unknown. Primary objectives of this study were to quantify dispersal rates among populations, to estimate metapopulation persistence, and to determine which factors (e.g. field area, interpatch), affect dispersal and persistence. We color-banded bobolinks (Dolichonyx oryzivorus) and monitored their locations throughout and among breeding seasons. We used a multistate movement model to analyze the capture-resight data, and to test hypotheses about sources of variation in dispersal patterns. To estimate population and metapopulation persistence probabilities we performed a population viability analysis in program RAMAS GIS. We captured 205 bobolinks during 2001-2004. Of the 123 birds resighted, 8% dispersed up to 14 km to a different field from where they were captured. Survival rate appears to be constant among populations, whereas dispersal probabilities vary by location. Results from population viability models will be discussed. Our findings could help balance the needs of agriculture with the needs of grassland-dependent birds.