The spotted underwing coverts and dark secondaries indicate immaturity. These heavy but stunningly graceful seabirds took advantage of updrafts created by our cruise ship. They would often hang overhead above the rear deck, or quarter back and forth, rarely plunging for food. They take 4-5 years before acquiring full adult plumage. Plumage stages between Juvenile and Adult are poorly understood. We know that they gradually (3–4 yr) develop all-white body plumage but Gannets of the same age show much variation because of individual differences in the progress of molt. Adults are known to have an alternate (breeding) plumage, but a pre-alternate molt has not yet been described for immature birds such as this.
This species has been increasing on both sides of the Atlantic and recently expanded northward into the Barents Sea, possibly as a consequence of warming ocean temperatures. The 2016 population in Norway was estimated at 6,900 breeding pairs in 7 colonies. However this is minuscule (2%) compared to the 340,000 occupied sites in 21 colonies in the British Isles.
Canon SX50 HS PowerShot
References:
Barrett, Robert T.; Strøm, Hallvard; Melnikov, Mikhail (2017). "On the polar edge: the status of the northern gannet (Morus bassanus) in the Barents Sea in 2015–16". Polar Research. 36 (1):1390384 https://doi.org/10.1080/17518369.2017.1390384
Carboneras, C., Christie, D.A., Jutglar, F., Garcia, E.F.J. & Kirwan, G.M. (2018). Northern Gannet (Morus bassanus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/52617 on 29 August 2018).
Mowbray, T. B. (2002). Northern Gannet (Morus bassanus), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.693