Building façade-level correlates of bird-window collisions in a small urban area

Urbanization increasingly exposes birds to multiple sources of direct
anthropogenic mortality. Collisions with buildings, and windows in
particular, are a top bird mortality source, annually causing 365-988
million fatalities in the United States. Correlates of window collision
rates have been studied at the scale of entire buildings and in relation
to the surrounding landscape, and most studies have only assessed
correlates for all birds combined without considering season- and
species-specific risk factors. In Stillwater, Oklahoma, USA, we conducted
bird collision surveys at 16 buildings to assess building structural-,
vegetation-, and land cover-related collision correlates. Unlike past
studies, we focused at the scale of individual building façades, and in
addition to considering correlates for total collisions, we assessed
correlates for different seasons and separately for eight collision-prone
species. Several façade-related features, including proportional glass
coverage, façade length, and façade height, were positively associated
with total collisions and collisions for most separate seasons and
species. Total collisions were also greater at alcove-shaped façades than
flat, curved, and portico-shaped façades. We found that collision
correlates varied among seasons (e.g., surrounding lawn cover important in
summer and fall, but not spring) and among species (e.g., surrounding
impervious cover positively and negatively related to collisions of
Painted Bunting and American Robin, respectively). Given the importance of
glass proportion, collision reduction efforts should continue to focus on
minimizing and/or treating glass surfaces on new and existing buildings.
Our species and season-specific assessments indicate that management of
some collision risk factors may not be equally effective for all seasons
and species. Future research, policy, and management that integrates
information about collision risk for all bird species and seasons, and at
multiple scales from building façades to the surrounding landscape, will
be most effective at reducing total mortality from bird-window collisions.