Evolving Bird Management Research at the USDA Wildlife Service’s National Wildlife Research Center

As the methods-development arm of the U.S. Department of Agriculture’s Wildlife Services program, the National Wildlife Research Center (NWRC) is charged with developing tools and information for protecting agriculture, human health and safety, and property from problems caused by wildlife, including birds. Increasingly the NWRC is being asked to provide basic ecological information on the population status of various bird species, and its role is expanding from a reactive one of providing management options to that of predicting long-term implications of various management actions. This paper describes several areas of research by NWRC scientists to address population-level questions in support of WS mission.

A Model-Based Approach for Making Ecological Inference from Distance Sampling Data

We consider a fully model-based approach for the analysis of distance sampling data. Distance sampling has been widely used to estimate abundance (or density) of animals or plants in a spatially explicit study area. There is, however, no readily available method of making statistical inference on the relationships between abundance and environmental covariates. Spatial Poisson process likelihoods can be used to simultaneously estimate detection and intensity parameters by modeling distance sampling data as a thinned spatial point process. A model-based spatial approach to distance sampling data has three main benefits: it allows complex and opportunistic transect designs to be employed, it allows estimation of abundance in small subregions, and it provides a framework to assess the effects of habitat or experimental manipulation on density. We demonstrate the model-based methodology with a small simulation study and analysis of the Dubbo weed data set. In addition, a simple ad hoc method for handling overdispersion is also proposed. The simulation study showed that the model-based approach compared favorably to conventional distance sampling methods for abundance estimation. In addition, the overdispersion correction performed adequately when the number of transects was high. Analysis of the Dubbo data set indicated a transect effect on abundance via Akaike’s information criterion model selection. Further goodness-of-fit analysis, however, indicated some potential confounding of intensity with the detection function.