Identification of extra-limital 'dark rumped' storm-petrels can be difficult and has been much-discussed in the literature. The left-hand photo shows a a Matsudaira's Storm-petrel which is flying actively past, with the carpal held well forward, the wings angled back and the 'arm' held angled in towards the body. The central photo shows a bird 'holding' over a feeding area, with the wings held out fully from the body and slightly forward. The right-hand photo depicts a bird gliding away but yet to adopt truly active, purposeful and rapid flight. Note how the apparent proportions of the wing (the aspect ratio) and the wing-length in proportion to the body-length are dependent upon the wing-set and flight action. Also note that the tail-fork is difficult to see unless the bird is viewed 'in plan'. This can be compounded by the fact that the tail is often held closed and that the fork in the tail is then effectively invisible. These photos have been selected as they show not only the structural features (and their apparent variability) but also show clearly the white patch at the base of the primaries. At close range this can be a conspicuous feature and on many individuals displays a noticeably 'hooked' outine. However, at medium and long range and in poorer light, the patch can be difficult or impossible to discern.

© A. R. Dean