Birds breeding in Alaska average larger than those in California. It is disputed whether U. a. inornata occurs in California in the winter, but there is published evidence that it does and the two races may be field-separable. Alaska race U. a. inornata average more white, less dusky in their underwings and less flank streaking. A recently published theory on egg shapes suggests that strong flyers have narrower eggs. That makes sense, but the authors' explanation of asymmetry seems less compelling. Common Murre eggs are strongly asymetric, almost pear-shaped while those of the closely related Thick-billed Murre (U. lomvia) are not. Canon PowerShot SX50 HS.
References:
Ainley, David G., Daivd N. Nettleship, Harry R. Carter and Anne E. Storey.(2002).Common Murre (Uria aalge), The Birds of North America (P. G. Rodewald, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/commur
Birkhead, T.R., Thompson, J.E. & Biggins, J.D. (2017) Egg shape in the Common Guillemot Uria aalge and Brunnich’s Guillemot U. lomvia: not a rolling matter? J Ornithol 158: 679. https://doi.org/10.1007/s10336-017-1437-8
Nettleship, D.N., Kirwan, G.M., Christie, D.A. & Boesman, P. (2017). Common Murre (Uria aalge). 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 http://www.hbw.com/node/54060 on 27 July 2017).