Importance of island-scale conservation for protecting sea eagle nesting habitat

Protection of islands offers opportunities to efficiently achieve conservation goals. However, islands can be profoundly different from mainland systems and specific understanding of island biota is necessary to inform management. For example, sea eagle ( Haliaeetus ) species may relax widely held habitat requirements when nesting on islands, which have different habitat availability and threatening processes from the mainland. We used maxent species distribution models and structural equation modelling to investigate nesting habitat of White-bellied Sea-Eagles ( H. leucogaster ) in the Houtman Abrolhos Islands, Western Australia. These islands lack the nest substrates, tall trees and cliffs, typically used by sea eagles. However, absence of predators and low levels of threats allow White-bellied Sea-Eagles to nest at or near ground level. We found that most habitat selection occurred at the island level, with White-bellied Sea-Eagles nesting on large islands and islands with abundant foraging resources, and avoiding islands disturbed by anthropogenic activities. Within islands, nest sites were strongly associated with proximity to the coast, with weaker effects of variables related to the physical stability of the site (vegetation density, geomorphic substrate). The Houtman Abrolhos Islands support a notable abundance of breeding White-bellied Sea-Eagles. However, the eagles nesting there may be unusually sensitive to human disturbances given the exposed nature of nests. Anthropogenic impacts are currently low, but likely to increase with climate change and expanding nature-based tourism. We advocate for conservation actions to be performed at the island level, rather than in exclusion zones surrounding individual nests, to maintain robust White-bellied Sea-Eagle breeding activity.