Presence, precipitation, and temperature data used to estimate eastern forest songbird historical distributions using climatic niche modeling

Boundaries between vegetation types, known as ecotones, can be dynamic in
response to climatic changes. The North American Great Plains includes a
forest-grassland ecotone in the south-central United States that has
expanded and contracted in recent decades in response to historical
periods of drought and pluvial conditions. This dynamic region also marks
a western distributional limit for many passerine birds that typically
breed in forests of the eastern United States. To better understand the
influence that variability can exert on broad-scale biodiversity, we
explored historical longitudinal shifts in the western extent of breeding
ranges of eastern forest songbirds in response to the variable climate of
the southern Great Plains. We used climatic niche modeling to estimate
current distributional limits of nine species of forest-breeding
passerines from 30-year average climate conditions from 1980 to 2010.
During this time the southern Great Plains experienced an unprecedented
wet period without periodic multi-year droughts that characterized the
region’s long-term climate from the early 1900s. Species’ climatic niche
models were then projected onto two historical drought periods: 1952–1958
and 1966–1972. Threshold models for each of the three time periods
revealed dramatic breeding range contraction and expansion along the
forest-grassland ecotone. Precipitation was the most important climate
variable defining breeding ranges of these nine eastern forest songbirds.
Range limits extended farther west into southern Great Plains during the
more recent pluvial conditions of 1980–2010 and contracted during
historical drought periods. An independent dataset from BBS was used to
validate 1966–1972 range limit projections. Periods of lower precipitation
in the forest-grassland ecotone are likely responsible for limiting the
western extent of eastern forest songbird breeding distributions.
Projected increases in temperature and drought conditions in the southern
Great Plains associated with climate change may reverse range expansions
observed in the past 30 years.