Density, Occupancy and Richness of Colorado Breeding Grassland Birds: Estimation and Habitat Correlations

Principal Investigator: Paul Doherty
Graduate Student: Heather Tipton
Project Start Date: 08/04
Expected Completion Date: 12/06
Funding Agency: Colorado Division of Wildlife

Introduction:
Over the last 40 years, shortgrass prairie birds have shown consistent, widespread declines. These declines may be a result of anthropogenic changes to the prairie landscape such as land conversion/cultivation, alteration of native grazing assemblages and regimes, and fire suppression. As wildlife biologists have attempted to address these declines and better manage avian species of concern, they have focused on developing monitoring schemes and identifying avian-habitat associations. One potentially important habitat relationship is with one of the ecosystem’s remaining native grazers, the black-tailed prairie dog (Cynomys ludovicianus). Studies have suggested that prairie dog colonies have higher avian densities and are more species rich than uncolonized areas. However, methodologies widely used to estimate grassland bird population parameters to date have lacked at least one of two important considerations, namely attention to a probability-based sampling scheme and incorporation of detection probability into estimates of abundance/density. This project focuses on these methodology issues as well as habitat correlations. The information obtained will be useful in advancing monitoring methods for shortgrass prairie bird communities and in directing agency land management and acquisition/conservation efforts.

Application:
Estimation methods will be evaluated and applied to grassland bird populations in Colorado’s shortgrass prairie.

Objectives:
1) Evaluate occupancy and double observer methodologies (which incorporate detection error) to estimate density, occupancy and richness using a probability-based sampling scheme.

2) Apply these methods to examine and compare the density, presence, and richness of avian species across three strata (prairie dog colonies, uncolonized grassland, and dryland agriculture) in the shortgrass prairie ecosystem of eastern Colorado. In doing so, we will test the prediction that prairie dog colonies have higher densities, higher occupancy probabilities, and greater richness of grassland birds than other habitat types.

Progress: To date Heather Tipton has conducted a pilot study and is in the process of writing her proposal. Heather is continuing her coursework and will begin her first formal field season this spring. During the week of March 7th, Heather defended her thesis proposal.