Relationships between cattle grazing and Rio Grande wild turkeys in the southern Great Plains
Hall, Galon I.
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Previous studies on the response of female and male turkeys to grazing have produced conflicting results, warranting further investigation. Our objectives were to quantify habitat use by female Rio Grande wild turkeys (Meleagris gallopavo intermedia) during the nesting period and determine possible relationships between cattle grazing and nesting site selection. We also wanted to investigate changes in space use and pastures used by male Rio Grande wild turkeys in the presence and absence of cattle. From 2000-2004, we located 351 nesting sites from radio-transmittered birds in the Texas Panhandle and southwestern Kansas. A logistic regression model comparing nesting sites to random sites indicated horizontal visual obstruction, vertical visual obstruction, and percentage of bare ground provided the highest predictive power (P < 0.003) for nesting site selection. Agricultural and upland zones were used less than available and riparian zones were used more than available (P < 0.001) for nesting; grazed pastures were used less than available and non-grazed pastures were used more than available (P < 0.05) for nesting. Statistical differences in measured vegetative characteristics were found primarily in compositional components among vegetative zones; upland zone nesting sites had a higher percent shrub component (P < 0.001) and riparian zone nesting sites had a higher percent grass component (P < 0.001). There were no significant differences in measured vegetative characteristics among pasture types, but there were differences in what was available for nesting in grazed and non-grazed pastures. Grazed pastures consistently had less grass cover (P < 0.018) and more bare ground (P < 0.043). Because of cattle impacts on grass availability, grazing would likely have the highest impact on nesting in riparian zones due to the high use of grass in riparian zones as Rio Grande turkey nesting cover. An appropriate grazing plan to promote Rio Grande turkey nesting habitat would include grazing upland zones in the spring, when it likely has little impact on nesting site selection, and grazing riparian areas following nesting season. From 2000-2004, we recorded telemetry locations of radio-transmittered male turkeys in the Texas Panhandle and southwestern Kansas. Area-observation curves indicated that a minimum of 25 locations per bird were adequate for home range calculation. The average home range size for adult male birds on all study sites was 1,830 ha and for juvenile male birds on all study sites was 1,475 ha. Our analysis of home range sizes of male turkeys at the Matador study area contained a lot of variation, and there were too many confounding factors that influenced home range sizes. However, we did find that 52.6% of male home ranges contained a known anthropogenic food source. A more effective analysis of cattle relationships involved comparing individual male locations with cattle presence or absence. We found no selection for grazed or non-grazed pastures (p > 0.05) by male Rio Grande turkeys. This differs from reported female pasture use and indicated a difference between the sexes in response to grazing. Grazing at light to moderate intensities with periods of rest did not affect male turkey pasture use and continued to maintain open areas used by male turkeys for displaying purposes.