Review of the breeding biology of rufous crab hawk Buteogallus aequinoctialis (Aves: Accipitridae) across its distribution

The rufous crab hawk (Buteogallus aequinoctialis) is a crab-eating specialist restricted to South American mangroves. Even though it is considered Near Threatened, with presumed population declines, its breeding biology remains poorly studied. Here we combined a comprehensive review of literature, museum and citizen science data to address its breeding biology, gaps in our knowledge, and conservation implications. The species lays one egg on a large stick nest placed on mangrove trees 6 to 11 m above the ground. The ovoid eggs averaged 57.5 × 44.0 mm in size (n = 25), overlapping partially with B. anthracinus and B. gundlachii eggs. The breeding period differs among regions, starting earlier in the northern parts of the distribution and progressively later in the southern ones. This review also shows that the species nests only in mangrove trees, a vegetation type under threat, and that breeding records are unevenly distributed across its range. Very little has been published on the reproduction of the rufous crab hawk in the last 50 years, and we still lack proper information on most aspects of its breeding biology. Our review shows that we can improve our understanding of a species’ reproduction by using multiple sources of previously available data and therefore provide a better basis to assist in conservation measures.