Grant’s August, Vincent

‘band-rumped storm-petrel’ off Graciosa, early August 2012 (Vincent Legrand). Grant’s Storm-petrels are on average more square-tailed than Monteiro’s Storm-petrel. However, Flood and Fisher (2011) advise to exercise extreme caution as there is much overlap in this feature between taxa. This problem is accentuated in judging these features in field conditions by apparent variation caused by angle of view and posture of bird which is further complicated in varying weather conditions. The shape of the tail is best assessed on square-on photographs and the presence of a deep fork is a stronger feature than an apparent square ended tail, which could be a result of feathers being splayed.

‘band-rumped storm-petrel’ off Graciosa, early August 2012 (Vincent Legrand). Grant’s Storm-petrels are on average more square-tailed than Monteiro’s Storm-petrel. However, Flood and Fisher (2011) advise to exercise extreme caution as there is much overlap in this feature between taxa. This problem is accentuated in judging these features in field conditions by apparent variation caused by angle of view and posture of bird which is further complicated in varying weather conditions. The shape of the tail is best assessed on square-on photographs and the presence of a deep fork is a stronger feature than an apparent square ended tail, which could be a result of feathers being splayed.

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