Songbirds, Woodpeckers, and Others
Songbirds and woodpeckers, or passerine and near passerine species, comprise the majority of bird species in Yellowstone National Park. They are monitored through the willow–bird study, the breeding bird survey, and the forest burn survey.
Songbirds and willows
Scientists are studying how the growth of willows in Yellowstone's northern range might be affecting songbirds that use this habitat. Willows and other woody vegetation have been highly suppressed in Yellowstone's northern range since the early 1900s. The loss and low stature of willows has been attributed to several factors including elk herbivory, reduced beaver populations, consumption by fire, and/or climate change. Since 1997–1998, however, park biologists have observed that some willow stands in the northern range are expanding in height. Willow stands are one of a few deciduous wetland habitats in the Greater Yellowstone Ecosystem. Biodiversity is considerably higher in wetland habitat types than in adjacent grasslands, shrublands, and upland coniferous forests.
Several Yellowstone bird species only breed in willow communities including Wilson's warbler (Cardellina pusilla), willow flycatcher (Empidonax traillii), and gray catbird (Dumetella carolinensis). Willow growth has increased in some parts of the park's northern range, for reasons still being studied. An increase in willow growth may support re-colonization by these and other bird species.
Monitoring of willow–songbird communities in Yellowstone began in 2005. Using data collected through monitoring, scientists will compare the presence and abundance of breeding songbirds across the range of willow growth conditions found throughout Yellowstone's northern range. Over time, the study will be able to track changes in bird species composition as willow stands continue to change in structure.
Surveys of burned forests
Birds are among the first returning vertebrates to a fire-affected area. Birds that nest in cavities of trees depend on forest fires to provide their habitat—and different species depend on different effects of forest fires. For example, black-backed (Picoides arcticus), American three-toed (P. dorsalis), and hairy woodpeckers (P. villosus) use trees that burned in low to moderately severe fires, two to four years after the fire. Northern flickers move into severely burned areas three years after a fire. Standing dead trees left behind after a fire attract bark and wood-boring beetles—primary prey for woodpeckers. Nest cavities created by woodpeckers are used later by chickadees, nuthatches, and bluebirds.
Because fire size, frequency, and intensity is expected to increase with climate change, scientists are studying how the different bird species use different types of post-burn forests and they are developing monitoring methods for the future.