Restoring Early-Successional Shrubland Habitat for Black-Capped Vireos using Mechanical Mastication

Abstract

Disturbance-dependent shrublands and the birds that nest in them are declining due to factors that include fire suppression and tree encroachment. Mechanical treatments are often used to decrease the threat of wildfire in sensitive areas, such as the wildland-urban interface, and could be used for restoration. We evaluated the use of mechanical mastication (also called mulching or chipping) to restore early-successional structure to oak-dominated shrublands in Texas, which provide nesting habitat for the endangered black-capped vireo (Vireo atricapilla Woodhouse). After mastication, overall vegetation height remained low for at least four growing seasons (pretreatment: 2.9 ± 0.1 m, mean ± SE; year 4: 1.1 ± 0.1 m). Canopy-sized Ashe juniper (Juniperus ashei Buchholz) was eliminated by mastication for the duration of the study, but other woody species remained abundant, maintaining vegetation density below 1 m. Black-capped vireos foraged in the masticated areas during the first and second breeding seasons after treatment, and started nesting in them during the third breeding season. By the fourth breeding season, breeding pairs were more than twice as abundant as before mastication (mean of 8.7 vs. 3.7 territories) and nests were farther from existing trails (mean ± SE of 39.9 ± 8.2 m vs. 18.4 ± 3.5 m), indicating that the birds were using more of the available space for breeding. We did not find a difference in the probability of nests in masticated areas surviving over the 28-day period from egg laying to fledging compared to nests from other areas (95% CI 0.28–0.62 and 0.18–0.47, respectively). Mastication is an effective substitute for prescribed fire to restore early-successional structure in shrublands dominated by resprouting woody plants and can also provide short-term control of nonsprouting species.