Species, subspecies or morph—what was the Canary Islands Oystercatcher?

Abstract

Taxonomists now usually recognize 10 extant species of oystercatcher Haematopus, plus the extinct Canary Islands Oystercatcher Haematopus meadewaldoi. Molecular data, however, have recently been used to propose meadewaldoi as either a morph or a subspecies of Eurasian Oystercatcher Haematopus ostralegus. The morph option is untenable for multiple reasons, but we also find subspecies rank problematic given (a) the all-black plumage and (based on our examination of all known specimens) significantly larger bill of the Canarian taxon, and (b) the global acceptance of species rank for Variable Haematopus unicolor and South Island Oystercatchers Haematopus finschi, which are genetically as close as and morphologically closer than meadewaldoi is to ostralegus but which despite their sympatry rarely interbreed. This case illustrates the difficulties of assessing species rank in shallowly divergent, morphologically conservative groups of birds such as the oystercatchers.