Using Occupancy Models to Predict Grassland Bird Distributions in Southeastern Alberta

Abstract

Widespread population declines of grassland birds have stimulated a variety of conservation plans, many of which promote a landscape approach to conservation. Identifying needs for survival and reproduction, and prioritizing key habitat requirements that influence where species occur on the landscape is an essential first step to guiding long term management efforts. I used single-species, single-season occupancy models to (1) identify landscape factors influencing the distribution of grassland bird species, (2) generate predictions of species distributions in southeastern Alberta, and (3) evaluate the predictive performance of each species model with two sources of evaluation data. In 2012, I conducted three repeat surveys at each of 870 point count locations to generate occupancy models, and evaluated the predictive performance of each model using a partitioned data set from 2012 and an independent data set of 1398 point counts collected in 2011. Records of detection/non-detection were collected for: Baird's Sparrow (Ammodramus bairdii), Brown-headed Cowbird (Molothrus ater), Chestnut-collared Longspur (Calcarius ornatus), Clay-colored Sparrow (Spizella pallida), Horned Lark (Eremophila alpestris), Long-billed Curlew (Numenius americanus), Marbled Godwit (Limosa fedoa), McCown's Longspur (Rhynchophanes mccownii), Savannah Sparrow (Passerculus sandwichensis), Sprague's Pipit (Anthus spragueii), Upland Sandpiper (Bartramia longicauda), Vesper Sparrow (Pooecetes gramineus), Western Meadowlark (Sturnella neglecta), and Willet (Tringa semipalmata). Models that best explained detectability typically included both date and time of day of the survey. The amount of grassland on the landscape was a broadly useful measure in predicting occupancy. Variables describing landscape topography and the geographic location (i.e., latitude and longitude) also aided in understanding where species occur and provided a more complete explanation of resource selection. I show that the models generated for four species were accurate predictors of occupancy. The remaining models require further investigation to develop accurate predictions of occupancy, but are presented for exploratory purposes and can be used to guide and refine future predictive modelling efforts. I suggest that, depending on the application, these models and maps be used to guide local conservation plans for birds, and can be used as a valuable reference for prioritizing conservation activities in southeast Alberta. These models add to our understanding of resource selection at the landscape level, and can assist in the process of ensuring key habitats are identified and conserved.