An ecological vulnerability index to assess impacts of offshore wind facilities on migratory song-birds

As offshore wind (OSW) energy expands globally, migratory songbirds are at risk of mortality from collisions with turbine blades, though the magnitude of this threat, and which species are most vulnerable, remains poorly understood. Ecological vulnerability indices are commonly used to assess species’ susceptibility to harmful factors, with results used to direct scarce research and monitoring resources to species showing relatively high vulnerability. These indices are based on the traits that elevate a species risk to adverse impacts (sensitivity), the overlap in occurrence between a species and the potentially harmful agent (exposure), and the influence of this exposure on the species’ local or global persistence (resilience). We modified ecological vulnerability indices for seabirds to assess vulnerability of migratory songbirds to OSW related mortality. As a pertinent case study, we considered songbirds that fly across the Northwest Atlantic during their autumn migration. We utilized readily available information on each species’ migratory behavior, life history, and conservation status to calculate an index score that could range from 1 (lowest vulnerability) to 125 (highest vulnerability). We found scores of 3 to 55.2 for the 101 songbird species evaluated, with New World warblers (Parulidae) over-represented among the highest scoring species. We found the scores to be sensitive to uncertainty in index components, highlighting the importance of considering scoring uncertainty when evaluating ecological vulnerability indices. Finally, we found that for seven of the top ten highest scoring species, modest improvements in population trends had the potential to lower the scores substantially. Our methodology is readily applicable to other regions where OSW development is planned and songbird migration is common, allowing research and monitoring activities to be targeted to species most likely to be negatively affected by OSW facility encounters.

Methods
This dataset consists of processed Z-Scores used to produce the Migratory Corridor Score, a component of our vulnerability index. The Z-scores were produced using raw count data from Northwest Atlantic Seabird Catalog (NWASC) sightings and eBird citizen science observations from both offshore in the Northwest Atlantic and from Bermuda made in autumn. The NWASC was provided by the National Oceanic and Atmospheric Administration (NOAA) and contains data collected by NOAA, the United States Fish and Wildlife Service, and the Bureau of Ocean Energy Management. The NWASC contains offshore survey data (largely focusing on seabirds) from various state and federal agencies and non-profit groups and is housed at the NOAA National Centers for Coastal Ocean Science. eBird data was collected from the publicly accessible online interface.

We tallied the number of observations of each species from the three data sources. We normalized each of the three counts by estimated North American population size for each species which we obtained from The Partners in Flight (PIF) Population Estimates Database housed at the Bird Conservancy of the Rockies. We utilized the column "Population Estimate USA/Canada" in version 3.1 of the Population Estimates Database. We z-transformed the resulting normalized count data and selected the largest Z-score for each species.

The dataset provided here consists of the processed Z-scores. For access to the Northwest Atlantic Seabird Catalog please reach out to the National Centers for Coastal Ocean Science at NOAA (https://coastalscience.noaa.gov). For access to the raw eBird data please see (https://ebird.org/home) and for the PIF Population Estimates Database please see the Bird Conservancy of the Rockies (https://pif.birdconservancy.org/population-estimates-database/).