The Middle Rio Grande riparian forests provide habitat for a variety of breeding birds including a large population of black-chinned hummingbirds (Archilochus alexandri). Frequency and intensity of wildfire has increased in this forest due to a number of factors including proliferation of exotic plants such as saltcedar (Tamarix spp.) and Russian olive (Eleagnus angustifolia). In response, fuel reduction programs have been implemented to remove exotic vegetation and woody debris from the understory of the forest. We examined responses of riparian-nesting birds to fire and fuel reduction by monitoring abundance, nest site selection, and nest survival of black-chinned hummingbirds in control plots, fuel reduction plots, and post-wildfire sites from 2000 to 2008.
Results/Conclusions
Hummingbirds nested in the understory and canopy layers of control plots and constructed most of their nests in exotic plants. Following fuel reduction, hummingbirds increased use of cottonwood (Populus deltoides subs wislizenii) as a nest substrate. In post-wildfire sites, hummingbirds constructed most nests in native and exotic resprouts. Mean nest height was greatest in fuel reduction plots (8.3 m), intermediate in control plots (4.4 m), and lowest in post-wildfire sites (2.8 m). Control plots, which were the most structurally diverse, had higher abundance of hummingbirds than fuel reduction plots and post-wildfire sites. Logistic exposure analysis revealed that nest survival did not vary between control plots, fuel reduction plots, and post-wildfire sites, though survival rates of nests constructed low in exotic vegetation (57% ± 7%, 95% CI) were higher than those of nests constructed at greater heights in cottonwoods (0.35% ± 7%, 95% CI). Our results suggest that exotic vegetation increases productivity of hummingbirds by providing understory nest sites with high rates of survival. Though nests in the cottonwood canopy had lower survival rates, this stratum should be protected to maintain high breeding densities of hummingbirds and other riparian obligate species.
