Exotic grass alters micro-climate and mobility for northern bobwhite chicks

Conservation practices are designed to provide habitat conditions that meet the environmental requirements for species of conservation concern. However, exotic invasive grass species may reduce the efficacy of these practices because they disrupt biological processes. During 7 August-6 September 2001, we investigated 2 possible ecological impacts of bermudagrass (Cynodon dactylon) on northern bobwhite (Colinus virginianus) brood ecology in managed field margins (Laurens County, GA, USA) - reduction in mobility and increased thermal risk. We tested and compared movement rates using imprinted chicks as assays and the thermal environment using in situ temperature probes for bermudagrass and forb habitats. Furthermore, we built upon the existing thermal ecology of northern bobwhite literature and established thermal models to derive time-to-death values from our empirical data. Bermudagrass reduced movement times for chicks 5-days old (0.45 min slower in treatments with bermudagrass), but not for chicks 10-days old. Furthermore, temperatures reached higher daytime temperatures in bermudagrass plots (44.0° C vs. 40.1°C) and crossed the critical hyperthermia threshold more often (32% vs. 11%) than in forb-dominated habitats. Based on simulations, chicks would reach thermal death much earlier in bermudagrass regardless of age. Collectively, our results suggest that bermudagrass reduces habitat quality for bobwhites through reduced movement efficiency and increased thermal stress. Large-scale reductions in bermudagrass are unlikely because of its invasive nature and economic importance to agriculture. However, targeted control or suppression of bermudagrass prior to and following field fallowing is necessary to achieve the objectives of conservation programs for bobwhites and likely other ground-dwelling birds.