Northern bobwhites (Colinus virginianus) are a culturally and economically significant game bird characteristic of grassland landscapes throughout their range. Despite the variety of research conducted on this species for nearly a century, populations continue to steadily decline, raising concern for future populations and highlighting the need for region-specific research. My research was conducted at Burning Star State Fish and Wildlife Area in northeastern Jackson County, Illinois from 2020-2022. My research addressed the following two objectives to provide insight on the population ecology of bobwhites at this site: (1) investigate the impact of multiple woody cover types within the home ranges of wintering bobwhites, how that cover may interact with winter severity, and their impacts on pre-breeding season survival, and (2) investigate the density of over-wintering diurnal raptor species between landscape types and discuss how this may be influencing predation risk. For objective 1, I radio-marked 141 individuals of which 102 had ≥ 15 relocations for estimating home-range size, and 127 individuals had ≥ 5 relocations and were used in survival analyses. I used an extended cox proportional hazards global model with continuous variables at the home-range scale. Variables considered included interspersion and juxtaposition index of blackberry, aggregation index of blackberry, and total area of blackberry, early successional forest, trees, and autumn olive. In addition, I used year, winter severity index (a time-dependent covariate), and an interaction term for year and winter severity index. The global model including all variables was retained as the most parsimonious model. Increases in the aggregation index of blackberry, area of autumn olive, and area of early successional forest were associated with increased hazard while increases in the interspersion and juxtaposition index of blackberry, area of blackberry, and area of trees were associated with a reduced hazard (α<0.05). For objective 2, I conducted 34 point-count surveys of predatory raptors throughout 6 landcover types every two weeks from October 2021 – January 2022. Bald eagles and barred owls were removed from analyses as I either did not credit them as significant predators of bobwhites or were nocturnal species, respectively. Observations from the 6 landcover types were split into two detection models based on whether the landcover type was classified as “open area cover” with a 125 m buffer distance or as “closed canopy cover” with a 75 m buffer distance. A uniform detection function was identified as the most parsimonious model for both the open area cover and closed canopy cover type models. Open area cover had a higher but not statistically significant difference in raptor density. My study demonstrates that woody cover types within the home-ranges of over-wintering bobwhites have strong relationships with the survival of those individuals and that diurnal raptors do not appear to be heavily concentrated in woody landscapes as predicted.

The encroachment of rangelands by woody plants causes an imbalance in the grass:bush ratio leading to decline in ecosystem services including grazing capacity, biodiversity, and water yield. This study assessed the historical changes in woody cover, and the effects of bush clearing on water loss, atmospheric carbon uptake, herbaceous vegetation, and soil seed bank (SSB) dynamics. The study was conducted at Makapanstad (Radi and Maseding) and Kgomokgomo rangelands, North-West Province, South Africa. Landsat imagery was used to assess woody cover over 34 years (1984 - 2018) in a total area of 16 397 ha. Evapotranspiration (ET) and gross primary productivity (GPP) were assessed in cleared sites and their adjacent uncleared sites from 2013 to 2018. Woody plant densities, herbaceous composition, ground cover and biomass production were assessed in 24, 5×5-m plots distributed equally in three 2500-m2 bush-encroached blocks in each rangeland in February 2016. Three samples for soil nutrient analysis were collected 20-cm deep in each plot. Thereafter, half (1250-m2) of each block was mechanically cleared to make three replicates of cleared and uncleared microsites. Post-treatment survey of vegetation was conducted in February 2017. SSB was assessed for samples collected in April 2016 before bush clearing and in August, October and December 2016, and April and August 2017 in paired microsites. In 1984, herbaceous cover (humid + arid grasslands) dominated, accounting for 36% of the total area followed by woody cover (shrublands + bushlands) and unvegetated cover (bare soils + abandoned croplands), with respective proportions of 33 and 31%. There were substantial land cover changes over time, with shrub cover increasing linearly (r2 = 0.94, p < 0.05) at a rate of 0.26% year-1, increasing the total woody cover (TWC) to 38% in 2018. Cropland abandonment was the main driver of increase in shrub cover in the study area. Herbaceous cover declined with increase in TWC (r2 = 0.69), whereas bare soil cover increased (r2 = 0.70) with TWC over time. The main encroachers were Vachellia tenuispina at Radi, Vachellia tortilis at Maseding and Dichrostachys cinerea and V. tortilis at Kgomokgomo. Most of the woody species correlated with total N and clay content (r = 0.96; p < 0.05) in black vertic clay soils of Radi and Maseding, whereas non-leguminous species correlated with total N and C:N in the red-yellow apedal soils of Kgomokgomo. ET and GPP varied interannually in all rangelands and both declined significantly (p < 0.05) after bush clearing at Radi and Kgomokgomo but not at Maseding. ET increased with GPP in cleared (r2 = 0.50-0.59) and uncleared sites (r2 = 0.82-0.93) at Radi and they showed a strong relationship (r2 >0.70) in both sites at Maseding and Kgomokgomo. ET ranged from 0.26-0.46 and 0.48-0.97 Kg H2O m-2 day-1 in cleared and uncleared sites, respectively, at Radi and from 0.44-0.98 and 0.63-1.24 Kg H2O m-2 day-1 at Kgomokgomo. Total SSB densities (constituted mostly by early successional species) increased significantly (p < 0.05) to 2470, 1872 and 693 seeds m-2 at Radi, Maseding and Kgomokgomo, respectively, in cleared microsites in August 2017. Similarly, biomass production (BP) and basal cover (BC) were highest in cleared relative to uncleared microsites. Overall, increase in woody cover reduced herbaceous cover and this calls for bush control in the studied rangelands. The decline in ET after bush clearing suggested that bush clearing could be used to increase rangeland water yield. Increased SSB densities, BP and BC indicated that bush clearing facilitates passive restoration. / Thesis (PhD (Pasture Science))--University of Pretoria, 2020. / Agricultural Research Council / National Research Foundation / Plant Production and Soil Science / PhD (Pasture Science) / Unrestricted