Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 99-110).

There is little information comparing the impacts of bison and cattle grazing in the northern mixed-grass prairies; understanding which grazer to use for management is important. I collected data in sites grazed by bison or cattle using point counts to survey the songbird community, and habitat structure measurements. I used generalized- and non-linear mixed models to determine the relationships between grazers and habitat or songbird communities. Bison and cattle grazing caused changes in habitat structure, including decreased vegetation height and litter depth. Sprague’s pipits declined more steeply with bison grazing than with cattle grazing. 0.4 AUM/ha was an important threshold, because chestnut-collared longspurs increased in abundance at this stocking rate, and grasshopper sparrows decreased in abundance at this stocking rate. Either grazer is appropriate for managing for grassland birds. There is also an opportunity to encourage surrounding landowners to manage their lands for the benefit of wildlife.

Grassland bird species are declining more quickly than any other avian group within North America, possibly due in part to declines in nesting success. In 2009-2010, I monitored nests of five songbird species in southwestern Saskatchewan. Two 300-m² plots were located in each of 12 pastures, three of which were ungrazed controls. The remaining pastures had stocking rates ranging from 0.23 – 0.83 AUM/ha, which were grazed for 2-3 or >15 years. Stocking rate affected nest site selection by three species, suggesting that some pastures have a greater availability of nest sites than others. Logistic exposure nesting success models suggested a nonlinear effect of stocking rate on nesting success of Sprague’s Pipit in 2009. The nesting success of two species was negatively correlated with grazing duration in 2009 and 2010, respectively. To encompass the different habitat needs of each species, I suggest maintaining rangeland landscapes with a range of grazing treatments.

This study considered the long term effects and interaction between burning and grazing in the northern mixed-grass prairies on the grassland songbird community. Point counts were conducted to assess songbird species abundances in burned-grazed, burned-ungrazed, unburned-grazed, and unburned-ungrazed pastures along with habitat structure (litter depth, vegetation height and density) over a five year period; from the first year post burn in 2007 until the fifth year post burn in 2011. Generalized linear mixed models were used to analyse the interaction between year, burning, and grazing for songbird abundances and habitat structure. As time since burned increased, species abundances in burned-grazed pastures have become more similar with those in unburned-grazed while abundances in burned-ungrazed are becoming increasingly similar to those in unburned-ungrazed pastures. The effects of burning are different than those of grazing and both disturbances should be utilised in grassland management when possible.

There is little information comparing the impacts of bison and cattle grazing in the northern mixed-grass prairies; understanding which grazer to use for management is important. I collected data in sites grazed by bison or cattle using point counts to survey the songbird community, and habitat structure measurements. I used generalized- and non-linear mixed models to determine the relationships between grazers and habitat or songbird communities. Bison and cattle grazing caused changes in habitat structure, including decreased vegetation height and litter depth. Sprague’s pipits declined more steeply with bison grazing than with cattle grazing. 0.4 AUM/ha was an important threshold, because chestnut-collared longspurs increased in abundance at this stocking rate, and grasshopper sparrows decreased in abundance at this stocking rate. Either grazer is appropriate for managing for grassland birds. There is also an opportunity to encourage surrounding landowners to manage their lands for the benefit of wildlife.

Grassland bird species are declining more quickly than any other avian group within North America, possibly due in part to declines in nesting success. In 2009-2010, I monitored nests of five songbird species in southwestern Saskatchewan. Two 300-m² plots were located in each of 12 pastures, three of which were ungrazed controls. The remaining pastures had stocking rates ranging from 0.23 – 0.83 AUM/ha, which were grazed for 2-3 or >15 years. Stocking rate affected nest site selection by three species, suggesting that some pastures have a greater availability of nest sites than others. Logistic exposure nesting success models suggested a nonlinear effect of stocking rate on nesting success of Sprague’s Pipit in 2009. The nesting success of two species was negatively correlated with grazing duration in 2009 and 2010, respectively. To encompass the different habitat needs of each species, I suggest maintaining rangeland landscapes with a range of grazing treatments.

This study considered the long term effects and interaction between burning and grazing in the northern mixed-grass prairies on the grassland songbird community. Point counts were conducted to assess songbird species abundances in burned-grazed, burned-ungrazed, unburned-grazed, and unburned-ungrazed pastures along with habitat structure (litter depth, vegetation height and density) over a five year period; from the first year post burn in 2007 until the fifth year post burn in 2011. Generalized linear mixed models were used to analyse the interaction between year, burning, and grazing for songbird abundances and habitat structure. As time since burned increased, species abundances in burned-grazed pastures have become more similar with those in unburned-grazed while abundances in burned-ungrazed are becoming increasingly similar to those in unburned-ungrazed pastures. The effects of burning are different than those of grazing and both disturbances should be utilised in grassland management when possible.

Grassland birds are experiencing the most significant declines of any avian guild in North America. Grazing is an important tool to manage habitats for these species, as they respond to structural changes in vegetation, and grazing affects vegetation structure. I studied the impact of cattle stocking rates grassland songbird abundances, with upland and lowland habitats in Grasslands National Park, Saskatchewan, Canada, 2006 to 2012. I also examined relationships between songbird abundance and plant community composition. Generalized linear mixed models were used for analyses. Species differed in responses to increased grazing (0 to 0.85 AUM/ha); Sprague’s pipit responded negatively, whereas chestnut-collared longspur responded positively. Above average precipitation during the study likely reduced the grazing effects. Overall, a range of cattle stocking rates makes habitat available for a complete songbird community. Efforts focused on prairie conservation should manage grazing at stocking rates that produce habitats that are under-represented relative to surrounding grasslands.

Thesis (Ph. D.)--University of California, San Diego, 1998. / Vita. Includes bibliographical references (leaves 126-134).

Thesis (PHD)--University of Montana, 2009. / Contents viewed on April 9, 2010. Title from author supplied metadata. Includes bibliographical references.