Offshore wind energy is a growing industry in the United States, and
renewable energy from offshore wind is estimated to double the country's
total electricity generation. There is growing concern that land-based
wind development in North America is negatively impacting bat
populations, primarily long-distance migrating bats, but the impacts to
bats from offshore wind energy is unknown. Bats are associated with the
terrestrial environment, but have been observed over the ocean. In this
review, we synthesize historic and contemporary accounts of bats
observed and acoustically recorded offshore over North American waters
to ascertain the spatial and temporal distribution of bats flying
offshore. We integrate these records with studies of offshore bats in
Europe and of bat behavior at land-based wind energy studies to examine
how offshore wind development could impact North American bat
populations. We find that most offshore bat records are of long-distance
migrating bats and records occur during autumn migration, the period of
highest fatality rates for long-distance migrating bats at land-based
wind facilities in North America. We summarize evidence that bats may be
attracted to offshore turbines for roosting and foraging opportunities,
potentially increasing their risk of collision, but that higher wind
speeds offshore can potentially reduce the amount of time that bats are
exposed to risk. We identify knowledge gaps and hypothesize that a
combination of mitigation strategies may be the most effective approach
for minimizing impacts to bats and maximizing offshore energy
production.