Scholarship & Research
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Item Reproductive success and post-fledging behavior of red-tailed hawks (Buteo jamiacensis) in the Gallatin Valley, Montana(Montana State University - Bozeman, College of Agriculture, 1973) Johnson, Sara JaneItem Bird response to landscape pattern and disturbance across productivity gradients in forests of the Pacific Northwest(Montana State University - Bozeman, College of Letters & Science, 2007) McWethy, David Burch; Chairperson, Graduate Committee: Andrew HansenManaging forest lands for biodiversity is a common goal in the public and private forests of the Pacific Northwest and is typically achieved through harvests that result in an array of vegetation structural conditions that provide suitable habitat for a number of species. The assumption is made that the causative factors of biodiversity do not vary geographically and that silviculture, as a management tool, can be applied similarly across different biophysical locales. The primary aim of this research is to better understand how species respond to both local and landscape-scale forest structural conditions in landscapes with different levels of productivity (e.g. gross primary productivity). We hypothesized that the influence of landscape effects on bird richness, abundance and community organization would be more pronounced in highly productive environments. We also hypothesized that species response to disturbance would differ across gradients in ecosystem productivity. We predicted that bird diversity would increase with increasing disturbance extent where favorable climatic conditions result in high levels of competitive exclusion. Alternatively, we predicted that bird diversity would decrease with increasing disturbance extent when factors other than competition limit or regulate bird species diversity.Item Mexican Spotted Owl reproduction, home range, and habitat associations in Grand Canyon National Park(Montana State University - Bozeman, College of Letters & Science, 2008) Bowden, Timothy Scott; Chairperson, Graduate Committee: Mark L. Taper; David Willey (co-chair)Mexican spotted owls (Strix occidentalis lucida) are nocturnal avian predators that are widely distributed in the southwest U.S. and northern Mexico. In 1993, the lucida subspecies was listed as threatened in response to concern over the loss of forest habitats to which the owl is widely associated. However, in the northwestern corner of their range spotted owls primarily inhabit steep-walled rocky canyons. Owl populations inhabiting this region have received less attention than populations using forests, although, canyon populations are important to the persistence of the subspecies, and are subject to different environmental pressures. I investigated the breeding ecology and home range characteristics of Mexican spotted owls within Grand Canyon which supports both forest and rocky canyon habitat. During the study from 2004 - 2006, female fecundity (mean = 0.86), calculated as the number of female fledglings per paired female, was relatively high compared to values reported previously for Mexican spotted owls. Five adult male owls were radio-tracked during the breeding season. I used minimum convex polygons and fixed kernel estimates to describe home range size (mean = 356 ha and 372 ha, respectively) and generated adaptive kernels to describe areas of concentrated use within home ranges. I used GIS to describe vegetation and geology cover types associated with owl use areas. This information was used to determine if spotted owls used landscape cover types disproportionately to their availability. At a landscape level, spotted owl telemetry locations were positively correlated with piñyon-juniper vegetation that occurred within canyons as well as with the Redwall and Muav geologic layers (pItem Change in deciduous woody vegetation, implications of increased willow (Salix spp.) growth for bird species diversity, and willow species composition in and around Yellowstone National Park's Northern range(Montana State University - Bozeman, College of Letters & Science, 2009) Baril, Lisa Marie; Chairperson, Graduate Committee: Andrew J. HansenDeciduous woody vegetation (DWV) in Yellowstone's northern range is a rare, but important habitat type. Including willow, alder, aspen, and cottonwood, DWV was limited in height and areal extent since the early 1900s. Since the mid-1990s; however, DWV has increased in height and areal extent in some locations. Previous studies regarding DWV change have focused on quantifying change in vegetation growth in areas of limited extent and none have quantified increased DWV growth at the scale of the landscape. Furthermore, no studies have evaluated the implications for increased growth of DWV for wildlife in the region or how DWV species themselves may influence rates of growth. In this thesis I evaluate change in DWV within wetland and riparian areas using aerial photographs from 1991 and 2006. I also investigate how an increase in willow, the dominant component of DWV in the region, has likely influenced bird diversity. Finally, since willow species vary with respect to genetic limitations on growth and reproduction that in turn may influence observed patterns of growth; I examine willow species composition across the northern range. Results of the air photo interpretation revealed a 170% increase in DWV. Most plots that increased did so by recruitment rather than densification; however, DWV was difficult to detect below 100 cm indicating that the number of plots increasing by recruitment may have been overestimated. Bird community variables were examined in three willow growth conditions: height suppressed, recently released, and previously tall (tall prior to observed increase in growth). I found that willow structure generally increased in complexity from structurally simple height suppressed willows to structurally complex previously tall willows and that this allowed for greater bird richness, abundance, diversity, and the abundance of several willow dependent bird species. I also found that willow species composition was similar and diverse between the released and previously tall condition, but that the suppressed condition was dominated by a singe species. I conclude that increased DWV has allowed for greater bird diversity in the northern range and that increased willow growth in the suppressed condition may be influenced by species composition there.Item Patterns of distribution and factors influencing riparian breeding birds along the Yellowstone River in Montana(Montana State University - Bozeman, College of Letters & Science, 2009) Jones, Danielle Ann; Chairperson, Graduate Committee: Andrew J. HansenRiparian zones harbor some of the most diverse bird communities. However, most riparian zones have been significantly modified by human activities. It is important to identify relationships between riparian birds and characteristics of the environment to understand the potential influences of floodplain management on birds. I examined patterns of riparian bird species distribution, as well as the factors affecting occurrence and abundance of species along the Yellowstone River in Montana. Point counts were conducted and vegetation data collected at 234 locations along 725 kilometers of the river. Occupancy or linear regression models were used to estimate occurrence or abundance of 14 bird species. First, I examined patterns in the distribution of bird species and their habitats. A gradient exists along most rivers that represents downstream changes in environmental conditions; I expected the distribution of vegetation to reflect this gradient, and birds to respond to these changing habitat conditions. Mature cottonwood habitat types were identified using cluster analysis, and habitat was an important driver of bird occurrence and abundance. However, there was little evidence that habitats were organized along a downstream gradient. River location was very important to birds, even after accounting for the influence of habitat, suggesting that the distributions of bird species are related to gradients that are not always reflected by habitat. Second, I used model selection methods to investigate the influences of local habitat, forest cover, land use, and river location on the occurrence or abundance of bird species. There was strong evidence that these factors were important drivers of bird distribution, and the relative influences of each factor depended upon life history characteristics of each species. The effect of river location on the occurrence or abundance of species suggests that broad-scale influences are important predictors of bird distribution along rivers. River location may reflect unmeasured environmental resources (e.g. food) that are important to birds, or variation in a species' distribution within its range boundaries. The Yellowstone River may serve as a reference for understanding the factors influencing the distribution of birds along a river, and provide valuable information for the management of riparian species.