Demographic and Density Response of Northern Bobwhites to Pyric Herbivory of Non-Native Grasslands

Abstract

Usable space for northern bobwhites (Colinus virginianus) has declined significantly over the past 3 decades in Texas because non-native grasses have replaced native vegetation. We hypothesized that burning patches in pastures dominated by buffelgrass (Pennisetum ciliare) and Old World bluestems (Bothriochloa spp. and Dichanthium spp.) followed by livestock grazing would increase limiting habitat attributes, thereby increasing usable space and bobwhite demographic parameters and population densities. Our study was conducted during 2009–2011 in LaSalle County, Texas on a ranch dominated by non-native grasses. Our experimental design was composed of 2 blocks with two 240-ha pastures, one control (graze only), and one treatment (patch-burn and graze) in each. We estimated grass standing crop in grazing exclosures (June–September) and habitat attributes along transects (October) 2009–2011. Bobwhites were captured and monitored via radiotelemetry 2–3 times/wk during March–November. Means of vegetation metrics important to bobwhites such as bare ground, traversibility, and forb and subshrub cover were similar between control and treatment units in post-treatment years. However, grass standing crop tended to be lower in treatment (June and August 2010 and September 2011—110.5 ± 26.2 g/m2) compared with control units (June and August 2010 and September 2011—145.5 ± 58.6 g/m2). Plant species richness was also greater (21%) in treatment (4.6 ± 0.4/0.1 m2) compared with control units (3.8 ± 0.4/0.1 m2) during the last year of the study (P ≥ 0.057). Patch heterogeneity was increased in treatment units. There was an increase in bobwhite densities in treatment units, although demographic metrics remained similar between treatment and controls. Patch burning and grazing is a viable tool for managing monotypic non-native grasslands for bobwhites in semiarid environments.