Date of Award
Master of Science (MS)
Forestry and Environmental Conservation
Skip J. Van Bloem
Northern bobwhite (Colinus virginianus) populations have steadily declined since at least the 1960s. There are numerous factors that contribute to this decline, such as lack of prescribed fire, cleaner farming practices, change in land use, and increased urbanization. These factors have all contributed to the deterioration and fragmentation of bobwhite habitat. Despite the expansive literature at the local level on bobwhite habitat and management, much fewer studies have observed the range-wide decline and its associated factors. Adding to both local and range-wide literature on bobwhites is essential to overturn the range-wide decline.
This thesis delves into both a local and a range-wide study of bobwhite populations and their habitat. On a local scale, soils in coastal South Carolina are poorly-drained and provide a unique set of characteristics that can influence understory vegetation components (bare ground, grass, forbs, and shrubs). These poorly-drained soils have been thought to have lower quality bobwhite habitat. I conducted field work to see how poorly-drained soils, time since last burn, and basal area might affect the plant composition of early-successional habitat that is preferred by bobwhites. The only component of the understory that was sensitive to all of these factors was the grass component. Wildlife managers in South Carolina have specifically expressed concern about the amount of grasses on the landscape and we can therefore use soil drainage type, time since last burn, and basal area to guide them in manipulating grass response as necessary. Decreasing timber thinning intensity to yield greater basal areas in a location is one possible way to decrease the grass percentage. Increasing the fire frequency or changing the fire timing away from spring and summer burns can also help decrease grass abundance. The poorly-drained study sites were closer to optimum understory compositions than the well-drained sites. No specific combinations of soil drainage, time since last burn, and basal area generated the perfect 1:1:1 relationship in understory components. Perhaps the plasticity of the understory habitat components needed to support bobwhites is larger than we thought.
I also evaluated how time since last fire influenced bobwhite counts across the bobwhite’s range to determine if fire suppression could be a potential driver in the decline of the species. I used 31 years (1984-2015) of fire data from the monitoring trends in burn severity (MTBS) and burned area essential climate variable (BAECV) datasets to compare to breeding bird survey data of bobwhites. I used a geographically weighted regression (GWR) to identify if time since last burn affected bobwhite counts differently depending on location. Recently burned areas (1-3 years since last burn) were found to increase on average across the landscape for 16 consecutive years. An average of 31.2% of these burned areas were on a fire rotation of 1-5 years (burned on average 2 times per 6 years). I found that fire was an important factor in determining bobwhite abundance over much of the landscape and the positive effects of these burns on the understory vegetation decreased after about 7 years. The relationship between fire frequency and bobwhites varied substantially on a local level, which prevented me from determining a uniform range-wide relationship between fire frequency and bobwhite counts. In order to make specific predictions on bobwhite abundance based on fire, we need more factors to explain the model on a range-wide scale. This analysis helped me identify areas that might be important in future research of bobwhites and other factors that might be needed in future range-wide modeling, such as fire size and amount of usable space.
Garrett, James, "Forest Management Influences on Northern Bobwhite (Colinus virginianus) Habitat in the South Carolina Lowcountry and Range-wide" (2019). All Theses. 3199.