martes, 9 de julio de 2019

1st summer Northern Gannet pitfall for Brown Booby

On 6.7.2019 a brown and white gannet was seen off Arnao, Asturias (Saúl Rodríguez).  See two photos below. The bird was initially identified as a Brown Booby (Sula leucogaster) mostly on the basis of the face pattern and overall black and brown plumage.

© Saúl Rodríguez, 6.7.2019

© Saúl Rodríguez, 6.7.2019

On 9.7 Daniel López Velasco, after being contacted by Jorge Valella who initially realised the bird was not a Brown Booby, confirmed that the photos of the bird and initial thoughts of Jorge were right so the bird was indeed a 1st summer Northern Gannet (Morus bassanus).

Features pointing towards Morus were:

• Brown chest limit too far from the front edge of the wing compared with Sula leucogaster (see figure below)

• White rump (hardly visible in the photos)
• Dark underwings


Sula leucogaster  © Daniel López Velasco


Arnao photos were not taken close enough and face pattern strongly recalled that of Sula leucogaster but a better analysis of the bird shows worn feathers and a face pattern that could be caused by moulted feathers into white, therefore matching at distance the leucogaster pattern. The rather ‘milk chocolate’ colour is paler than that expected for a leucogaster, richer and darker.

This bird really stands out the difficulties of accepting a distant Brown Booby sighting in this part of the year if it is not properly seen and even photographed.

Thanks to Jorge Valella and Dani López por pointing out this interesting pitfall.