A critical look at the evidence relating to 'the Chalice petrel'

This paper presents a critical review of the field evidence relating to a record of a dark-rumped storm-petrel Oceanodroma, seen from the M.V. Chalice, southwest of Scilly, on 3rd August 1988 ('the Chalice petrel'). We contend that a critical misjudgment of the size of the Chalice petrel has seriously hampered the subsequent debate about its identity, and that it can, in fact, be shown to be approximately the same size as a Leach's Storm-petrel O. leucorhoa. It seems likely that the unfamiliar flight action of the mystery petrel may have contributed significantly to the impression of a larger-looking seabird, as well as the fact that it was being compared directly with the much smaller European Storm-petrel Hydrobates pelagicus. Its size and other features are discussed here, together with a subsequent and well-documented record of a Swinhoe's Storm-petrel O. monorhis, seen from a boat in the western North Atlantic. Given the North Atlantic context of the Chalice petrel, we believe that the evidence points to it having been a Swinhoe's Storm-petrel.