Leucistic Cory’s Shearwater Calonectris borealis off São Miguel, Azores, in November 2019

Abstract

The Cory’s Shearwater Calonectris borealis is the most abundant seabird in the Azores. It breeds along the coast of all islands and on most islets in the archipelago (Monteiro et al. 1996a). Birds attend colonies and adjacent waters from late February to late October (Monteiro et al. 1996b), when they can be seen daily around most islands. From mid-November to late January most birds have migrated to wintering areas in the tropical and southern Atlantic (Camphuysen & van der Meer 2001; González-Solís et al. 2007). Aberrant colourations such as albinism, leucism, and melanism have been reported in a wide range of seabird species. One of the aberrant colourations, leucism, is defined as a loss of pigment of entire feathers. A loss of pigmentation may also occur in the legs and bill however, excluding a change in colour of the eyes (van Grouw 2006). This loss of pigmentation, or lack of eumelanin, is due to congenital and heritable failure of pigment-producing melanoblasts to reach some or all areas of the skin (van Grouw 2013). In this note, we document an observation of an aberrantly coloured Cory’s Shearwater in the Azores.