Straight-billed Gaper (Aidemedia chascax)  

The Straight-billed Gaper, described in 1991 based on subfossil remains, is known only from the island of O’ahu, Hawaiian Islands, where it lived sympatrically with another species of its genus, the Sickle-billed Gaper (Aidemedia zanclops James & Olson).  

These two species differed mainly in the shape and size of their beaks, and it is assumed that they may represent males and females of a single, sexually dimorphic species. [1]  

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References:  

[1] S. L. Olson; H. F. James: Descriptions of thirty-two new species of birds from the Hawaiian Islands: Part II. Passeriformes. Ornithological Monographs 45: 1-91. 1991  

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edited: 22.03.2018