Data from: Consequences of habitat change and resource selection specialization for population limitation in cavity-nesting birds

Resource selection specialization may increase vulnerability of
populations to environmental change. One environmental change that may
negatively impact some populations is the broad decline of quaking aspen
Populus tremuloides, a preferred nest tree of cavity-nesting organisms who
are commonly limited by nest-site availability. However, the long-term
consequences of this habitat change for cavity-nesting bird populations
are poorly studied. I counted densities of woody plants and eight
cavity-nesting bird species over 29 years in 15 high elevation riparian
drainages in Arizona, USA. I also studied nest tree use and specialization
over time based on 4946 nests across species. Aspen suffered a severe
decline in availability over time, while understorey woody plants and
canopy deciduous trees also declined. The decline of plants resulted from
increased elk Cervus canadensis browsing linked to declining snowfall.
Woodpeckers exhibited very high specialization (>95% of nests) on
aspen for nesting, and densities of all six species declined with aspen
over time. Mountain chickadees Poecile gambeli and house wrens Troglodytes
aedon exhibited increasingly less specialization on aspen. Chickadees
strongly increased in density over time, despite a relatively high
specialization on aspen. House wren densities declined moderately over
time, but nest box addition experiments demonstrated that nest-site
availability was not limiting their population. House wren densities
increased with understorey vegetation recovery in elk exclosures via
increased generality of nest site use, demonstrating that the decline in
understorey vegetation on the broader landscape was the cause of their
population decline. Synthesis and applications. Management should target
species that specialize in resource selection on a declining resource.
Species with greater resource selection generalization can reduce
population impacts of environmental change. Resource generalization can
allow a species like the wren to take advantage of habitat refuges, such
as those provided by the elk exclosures. Yet, resource generalization
cannot offset the negative impacts of broad-scale declines in habitat
quality on the landscape, as demonstrated by the general decline of wrens.
Ultimately, aspen is an important habitat for biodiversity, and land
management programs that protect and aid recovery of aspen habitats may be
critical.