One of two adult Kittiwakes seen this morning at the mouth of Pilarcitos Creek in Half Moon Bay. Kittiwake numbers seem to fluctuate dramatically from year to year. Note the dark "ear-muffs" typical of winter plumage. Pacific birds such as this are larger and have a longer bill than the nominate race of the North Atlantic. Interestingly Atlantic birds are more successful at reproduction, but Pacific kittiwakes live longer. Digiscoped with Panasonic DMC-LX5 | Nikon FieldScope III | 30XWA | hand-held (no adapter)
References:
Burger, J., Gochfeld, M., Kirwan, G.M., Christie, D.A., Garcia, E.F.J. & Sharpe, C.J. (2020). Black-legged Kittiwake (Rissa tridactyla). 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/54010 on 8 February 2020).
Hatch, S. A., G. J. Robertson, and P. H. Baird (2009). Black-legged Kittiwake (Rissa tridactyla), version 2.0. In The Birds of North America (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.92
Howell, S.N.G. & Dunn, J.L. (2007) Gulls of the Americas. Houghton Mifflin, Boston.
Malling Olsen, K. & Larsson, H. (2003) Gulls of Europe, Asia and North America. Christopher Helm, London.