Hager SB, Craig ME. (2014) Bird-window
collisions in the summer breeding season. http://dx.doi.org/10.7717/peerj.460
Birds that reside in urban settings face numerous
human-related threats to survival, including mortality from bird-window
collisions (BWCs). Our current understanding of this issue has largely been
driven by data collected during spring and fall migration, and patterns of
collision mortality during the summer breeding season remain relatively
unexplored.
The
relationship between BWCs and abundance depended on age. For adults, BWCs were
highest in the least abundant species, e.g., Red-eyed Vireo (Vireo olivaceus),
and lowest in species with high abundance values, e.g., Chipping Sparrow (Spizella
passerina). For juveniles, mortality was greatest for the most abundant
species, and the American Robin (Turdus migratorius) accounted for 62%
of all juvenile carcasses. Early in the breeding season, collision mortality
was restricted to adults of Long-distance Migrants, whereas juveniles of all
three migratory guilds (Long-distance and Short-distance Migrants and Permanent
Residents) died at windows from late June through early August. Daily mortality
for all species was highest between sunrise–1600 h and lowest from 1600
h–sunrise the next day.
Generally, the species observed as carcasses matched
birds considered a ‘high risk’ for BWCs, e.g., Ruby-throated Hummingbird (Archilochus
colubris), and those considered ‘low risk’ were not observed as carcasses,
e.g., Blue-gray Gnatcatcher (Polioptila caerulea). Our results suggest
that the number of BWCs during the breeding season does not necessarily
increase with abundance, but rather appears related to variation among species
and age classes, which may have important implications on the population health
of affected species. The mechanisms driving these differences are unknown, but
may be related reproductive behavior, flight speed, distance movements, and
dispersal patterns.
