Breeding biology and nesting behavior of the endemic subspecies of White-eyed Vireo ( Vireo griseus bermudianus ) on the Bermuda archipelago

Abstract

Avian island endemics are prone to extinction, and the preservation of remaining taxa requires long-term studies of their natural history and threats to survival. Thus, we provide, for the first time, a detailed account of the breeding biology and nesting threats of an endemic subspecies of vireonid, the non-migratory Bermuda White-eyed Vireo (Vireo griseus bermudianus). From 2016–2021, we located 84 nests, collected breeding data associated with 47 breeding pairs, and conducted observations throughout the nesting cycle. Some breeding pairs remained together for up to four successive breeding seasons. Bermuda Vireos began building nests in late February and cared for fledglings until mid-August. Both sexes contributed to all nesting stages, which were similar in duration to those of other vireo species (N, mean ± standard deviation): nest building (13 nests, 6 ± 3 d), incubation (11 nests, 14 ± 2 d), nestling care (6 nests, 11 ± 2 d), and fledgling care (5 nests, 41 ± 12 d). Nests, eggs, and nestlings were all vireonine in structure and appearance; nests were found in 14 tree species (2 endemic, 2 native, and 10 introduced). Across six years, 25 of the 42 nests (60%) with eggs produced nestlings, and 10 of the 25 broods (40%) produced fledglings; introduced predators were likely the primary cause of nest failure (16 of 27 nests, 59%). The Bermuda White-eyed Vireo is the last endemic terrestrial bird that breeds on the island and is of local conservation importance. Our observations should prove beneficial to other researchers interested in the breeding biology and nesting threats of breeding vireo species beyond Bermuda and for creating effective recovery plans necessary for conservation and management. © 2023 by the author(s).