Landscape, Legal, and Biodiversity Threats that Windows Pose to Birds: A Review of an Important Conservation Issue
Windows in human residential and commercial structures in urban, suburban, and rural landscapes contribute to the deaths of billions of birds worldwide. International treaties, federal, provincial, state, and municipal laws exist to reduce human-associated avian mortality, but are most often not enforced for bird kills resulting from window strikes. As an additive, compared to a compensatory mortality factor, window collisions pose threats to the sustainability and overall population health of common as well as species of special concern. Several solutions to address the window hazard for birds exist, but the most innovative and promising need encouragement and support to market, manufacture, and implement.
Factors influencing the annual risk of bird–window collisions at residential structures in Alberta, Canada
Abstract Context. Increasingly, ornithologists are being asked to identify major sources of avian mortality so as to identify conservation priorities. Aims. Considerable evidence suggests that windows of office towers are a lethal hazard for migrating birds. The factors influencing the risk of bird–window collisions in residential settings are not understood as well. Methods. Citizen scientists were requested to participate in an online survey that asked about characteristics concerning their homes and yards, general demographic information about participants, and whether they had observed evidence of bird–window collisions at their home. Key results. We found that 39.0% of 1458 participants observed a bird–window collision in the previous year. The mean number of reported collisions was 1.7 ± 4.6 per residence per year, with 38% of collisions resulting in a mortality. Conclusions. Collisions were not random, with the highest collision and mortality rates at rural residences, with bird feeders > rural residences without feeders > urban residences with feeders > urban residences without feeders > apartments. At urban houses, the age of neighbourhood was a significant predictor of collision rates, with newer neighbourhoods reporting fewer collisions than older neighbourhoods. Most people remembered collisions occurring in the summer months. Implications. Our results are consistent with past research, suggesting that window collisions with residential homes are an important source of mortality for birds. However, we found large variation in the frequency of collisions at different types of residences. Proper stratification of residence type is crucial to getting accurate estimates of bird–window collisions when scaling local data into larger-scale mortality estimates.
Novel Scavenger Removal Trials Increase Wind Turbine–Caused Avian Fatality Estimates
Abstract For comparing impacts of bird and bat collisions with wind turbines, investigators estimate fatalities/megawatt (MW) of rated capacity/year, based on periodic carcass searches and trials used to estimate carcasses not found due to scavenger removal and searcher error. However, scavenger trials typically place ≥10 carcasses at once within small areas already supplying scavengers with carcasses deposited by wind turbines, so scavengers may be unable to process and remove all placed carcasses. To avoid scavenger swamping, which might bias fatality estimates low, we placed only 1–5 bird carcasses at a time amongst 52 wind turbines in our 249.7-ha study area, each carcass monitored by a motion-activated camera. Scavengers removed 50 of 63 carcasses, averaging 4.45 days to the first scavenging event. By 15 days, which corresponded with most of our search intervals, scavengers removed 0% and 67% of large-bodied raptors placed in winter and summer, respectively, and 15% and 71% of small birds placed in winter and summer, respectively. By 15 days, scavengers removed 42% of large raptors as compared to 15% removed in conventional trials, and scavengers removed 62% of small birds as compared to 52% removed in conventional trials. Based on our methodology, we estimated mean annual fatalities caused by 21.9 MW of wind turbines in Vasco Caves Regional Preserve (within Altamont Pass Wind Resource Area, California, USA) were 13 red-tailed hawks (Buteo jamaicensis), 12 barn owls (Tyto alba), 18 burrowing owls (Athene cunicularia), 48 total raptors, and 99 total birds. Compared to fatality rates estimated from conventional scavenger trials, our estimates were nearly 3 times higher for red-tailed hawk and barn owl, 68% higher for all raptors, and 67% higher for all birds. We also found that deaths/gigawatt-hour of power generation declined quickly with increasing capacity factor among wind turbines, indicating collision hazard increased with greater intermittency in turbine operations. Fatality monitoring at wind turbines might improve by using scavenger removal trials free of scavenger swamping and by relating fatality rates to power output data in addition to rated capacity (i.e., turbine size). The resulting greater precision in mortality estimates will assist wildlife managers to assess wind farm impacts and to more accurately measure the effects of mitigation measures implemented to lessen those impacts.