Tracking data highlight the importance of human-induced mortality for large migratory birds at a flyway scale

Human-induced direct mortality affects huge numbers of birds each year, threatening hundreds of species
worldwide. Tracking technologies can be an important tool to investigate temporal and spatial patterns of bird
mortality as well as their drivers. We compiled 1704 mortality records from tracking studies across the AfricanEurasian flyway for 45 species, including raptors, storks, and cranes, covering the period from 2003 to 2021. Our
results show a higher frequency of human-induced causes of mortality than natural causes across taxonomic
groups, geographical areas, and age classes. Moreover, we found that the frequency of human-induced mortality
remained stable over the study period. From the human-induced mortality events with a known cause (n = 637),
three main causes were identified: electrocution (40.5 %), illegal killing (21.7 %), and poisoning (16.3 %).
Additionally, combined energy infrastructure-related mortality (i.e., electrocution, power line collision, and
wind-farm collision) represented 49 % of all human-induced mortality events. Using a random forest model, the
main predictors of human-induced mortality were found to be taxonomic group, geographic location (latitude
and longitude), and human footprint index value at the location of mortality. Despite conservation efforts,
human drivers of bird mortality in the African-Eurasian flyway do not appear to have declined over the last 15
years for the studied group of species. Results suggest that stronger conservation actions to address these threats
across the flyway can reduce their impacts on species. In particular, projected future development of energy
infrastructure is a representative example where application of planning, operation, and mitigation measures can
enhance bird conservation.