Small urban green spaces attract migratory birds and may allow them to refuel during migration stopovers. Due to large-scale habitat fragmentation, such small green spaces are becoming more important in particular along the heavily urbanized section of the Atlantic flyway. However, besides providing needed place for rest and forage, such places also create hazards that include mortality due to window strikes. The urban campus of Rutgers Newark provides small green spaces that are managed as urban “biodiversity havens” and act as stopover sites for migratory birds. Many previous studies have documented the absolute number of birds striking windows in urban areas but much less information is available about the percentage of the bird community that is affected. Therefore we analyze here a long-term data set (2007-2014) that combines bird counts with systematic quantification of window strikes. In particular we ask what percentage of the bird community is affected by window strikes, and what species are more at risk than others.
Results/Conclusions
On average 4% of recorded bird individuals were found to strike windows (1.7% observed as killed, 2.5% as stunned). However this percentage included residents with very low strike incident rates and migratory species with much higher rates (up to 13%). In particular migratory species that forage close to the ground (e.g., American Woodcock, Ovenbird, Common Yellowthroat, etc.) were more prone to window strikes. This can be explained by the high proportion of buildings with glass surfaces at ground level at the Rutgers Newark campus. It is interesting however, that ground-foraging species that tend to stay for longer periods (e.g., migrating and wintering White-throated Sparrows) were relatively less affected. Our data indicate that window impact can affect a significant portion of migratory birds, in particular ground foraging species that use wild urban patches to forage. The number of birds using the stopover site steadily increased over the year which is likely the direct result of managed habitat improvements. At the same time the rate of widow kills decreased on average from 5 to 1 percent. We hypothesize that this is also the result of habitat improvement.