American pikas select fine-scale characteristics of talus patches for haypile locations

Abstract The American Pika (Ochotona princeps) does not hibernate and relies on caching vegetation in haypiles to survive during the winter when vegetation is scarce. Although many studies have evaluated the influence of patch-scale features on habitats selected by these obligate rock-dwellers, little is known about how fine-scale rock characteristics affect pika haypile site selection because of challenges in collecting systematic, high-resolution data in talus patches. Therefore, we used hand-held photogrammetry techniques to measure rocky habitats at an extremely fine resolution (∼1 mm). We characterized the size and shape of all rocks, surface roughness, and vegetation cover within plots at 40 sites within the North Cascades National Park and Mt Baker-Snoqualmie National Forest in Washington. We collected and processed 3 sets of images per site: 1 3 × 3 m plot containing haypiles; and 2 associated unused control plots in a matched case–control design. We compared models predicting haypile site selection from these metrics and 2 patch-level metrics, distance to patch edge and vertical position within the talus patch. The top model predicting haypile site selection included rock size (maximum area), shape (flatness), surface roughness, and vegetation cover. Pikas selected areas for their haypiles with larger and flatter rocks and rougher surfaced areas with less vegetation than control plots. Patch-level variables and the model with patch-level variables alone did not perform better than the null model. Using a portable and easy-to-apply photogrammetry method, we demonstrated that pikas respond to fine-scale rock characteristics when selecting haypile sites. These findings provide a starting point for exploring how such behavioral choices may influence individual fitness and population persistence of pikas under changing environmental conditions.