Author: Michael Clayton McGrann

Publisher:

Published: 2011

Total Pages:

ISBN-13: 9781124665993

The Pacific Crest Trail (PCT) runs along the California cordillera and it affords an excellent opportunity to study bird species distributions, bird species richness patterns, and bird-habitat relationships along elevation gradients and across ecoregions. In the spring and summer of 2006, I performed mega-transect survey along the PCT, where I collected bird-habitat data from 3,578 survey plots that were systematically established at 10-minute walking intervals. This mega-transect included the entire 2,736 km-length of the PCT in California, from 32.58° N to 42.00° N. In Chapter 1 of this dissertation, I assessed the patterns of bird species diversity and individual bird species distributions of the most frequently detected birds along the PCT among 100 m zones of elevation and across ecoregions. I found that the mountains of southern California and the southern Cascade Ranges in the north exhibited the greatest species diversity. Additionally, relative frequencies of common bird species were rather low in the elevation zones with the maximum number of overlapping bird species ranges; these zones represented altitudinal range limits for most common bird species. Zones of maximum range overlap may harbor ecotones with marginal habitats. In Chapter 2, I investigated the effects of elevational changes in climate (i.e., temperature and precipitation) on richness patterns of songbird species and found that temperature exhibited a consistent relationship with bird species diversity, but precipitation was an inconsistent predictor across ecoregions. Lastly in Chapter 3, I analyzed classification system effects in wildlife habitat relationships by comparing both broadly and more narrowly defined vegetation classification schemes in bird habitat relationships. I found that bird community composition was organized based on more narrowly defined vegetation types within a more broadly defined Subalpine Conifer vegetation type at the regional (statewide) spatial extent. I recommend that more narrowly defined vegetation types should be incorporated in wildlife habitat relationship models by using a hierarchical system. Knowing how wildlife communities respond, if at all, to vegetation types are crucial for wildlife modeling and conservation planning.