Avian responses to prescribed burning in a shrub-encroached, semiarid grassland.

摘要

Fire suppression has promoted the encroachment of woody vegetation in grasslands worldwide. In southwestern North America, shrubs such as mesquite (Prosopis spp.) and cholla (Opuntia spp.) now dominate fire-suppressed, semiarid grasslands. Avian responses to fire management of shortgrass prairie in this region are poorly understood. We examined avian responses to prescribed burning in an experimental landscape (4811 ha) of spatially-replicated, inter-annual fire frequencies (burning every 2, 4, or 10 years) near Amarillo, Texas, USA. Using an information-theoretic model-selection procedure, we compared avian abundance, species richness and diversity, nest failure, and brood parasitism among the burn treatments (&ge2 months post fire) and several habitat covariates. Herbaceous habitat structure and large shrub (>1.5 m tall) density were greatest in infrequently-burned plots. Few bird species were grassland-dependent. Variation in avian abundance across the burn treatments was species-specific, which was reflected in uniform patterns of species richness and diversity. Nest success was low (2.3% to 22.4% among species). Daily nest mortality of Mourning Dove (Zenaida macroura) and Lark Sparrow (Chondestes grammacus) nests was higher in infrequently-burned plots. Brood parasitism of Lark Sparrow nests by Brown-headed Cowbirds (Molothrus ater) was most frequent in plots burned every 4 years. In semiarid grasslands heavily inundated with shrubs, prescribed burning can positively influence the abundance and nest success of some bird species, though responses of grassland-obligate birds may be delayed.Keywords: brood parasitism grassland birds nest success prescribed burning shortgrass prairie woody encroachment.