Breeding season bird mortality from window collisions: Comparing species-specific abundance with mortality rates

Abstract

The second largest anthropogenic cause of bird mortality in North America is bird-window collision, which kills 100s of millions of birds every year in the United States alone. Many studies have focused on documenting species-specific collision occurrences during the migration seasons, which are commonly thought to be the time of year with the highest rate of mortality. However, few studies have been conducted during periods when birds are sedentary. Similarly, only a small number of studies have attempted to compare collision occurrence to local abundance. To help fill these gaps, data on bird-window collisions was collected in a downtown busi- ness district including the collection of carcass (i.e. collisions) and local point counts (i.e. species frequency) during the summer breeding season. In total, 15 species were observed but only three species (house sparrow, house finch, and American robin) were observed both alive and dead. The other 12 species were either detect- ed alive but not found dead or found dead but not detected alive. This finding suggests that there is a discrep- ancy in collision likelihood among species that should be further studied to determine which traits are shared among those that collide more or less often relative to their abundance. Some traits which could be studied in- clude species origin (i.e. native or introduced), foraging style, nesting habits, mating patterns, flocking, age, or sex. With improved understanding of traits that make some species more prone to collisions than others, city planners and developers may be able to improve development strategies to decrease bird-window collisions.