Thesis (M.S., Environmental Science) -- University of Idaho, 2016 | Vegetation structure and composition are central to understanding avian-habitat relationships. Vegetation structure can be challenging to measure; however, 3-D LiDAR remote sensing provides a robust solution. My study utilized LiDAR-derived vegetation metrics to examine the relative influence of vegetation structure and canopy composition on 1) avian richness patterns and 2) occupancy of a cavity excavator, the Red-naped Sapsucker (Sphyrapicus nuchalis), across an aspen-conifer forest gradient in west-central Idaho. Quaking aspen (Populus tremuloides) enhances forest biodiversity but has been declining across western North America, often due to conifer encroachment. My study found evidence that 1) aspen has greater avian richness than conifer and mixed aspen-conifer, especially among cavity nesters and 2) conifer encroachment in aspen may be one mechanism that reduces occupancy of Red-naped Sapsuckers. Understanding vegetation-wildlife associations increases our ability to respond appropriately to habitat changes, such as declining aspen, and enhances our knowledge of the influence of vegetation on wildlife.