Unintended consequences: how the recovery of sea eagle Haliaeetus spp. populations in the northern hemisphere is affecting seabirds

Abstract

The recovery of sea eagle Haliaeetus spp. populations in the temperate northern hemisphere in the closing decades of the 20th century is one of the great conservation success stories of recent times, but the re-establishment of these apex predators in marine systems has had consequences for seabirds. Sea eagles affect seabirds both directly (by taking adults and offspring and by inducing potentially costly behaviors to minimize danger) and indirectly (by facilitating the nest predators of seabirds, mainly gulls and corvids). Repeated disturbance by hunting eagles has caused seabirds to abandon colonies and subcolonies in the tens to hundreds of thousands of pairs. In recent years, sea eagles have been widely implicated in local declines of surface-nesting seabirds in the northeast Pacific Ocean, the northwest Atlantic Ocean and northern Europe. The extent to which recent events simply reflect a return to a more “natural” ecological baseline as sea eagle populations recover from decades of persecution and chemical pollutants is discussed. We argue that there is need for a research effort to investigate the conservation implications of increasing sea eagles in the context of multiple threats to seabird populations.