A paper that I've been involved in for some time now, authored by Marcel Gil Velasco and Guille Rodríguez, has just been published:
Gil-Velasco, M., Rodríguez, G., Menzie, S. & Arcos, J.M. (2015). Plumage variability and field identification of Manx, Yelkouan and Balearic Shearwaters. British Birds 108 514–539
Three medium-sized Puffinus shearwaters breed in Europe: Manx P. puffinus, Yelkouan P. yelkouan and Balearic Shearwaters P. mauretanicus. These three, considered a single, polytypic species until relatively recently, can be difficult to identify in some situations, notably in a vagrant context. This paper presents a detailed review of the plumage variability of the three taxa; combined with an understanding of structural differences and flight characteristics, this should provide a sound basis for the identification of problematic individuals.
The plate on the left is my favourite from the paper; Marcel and Guille did a fantastic job of finding photographs that compliment each other – like this pair do.
There's also some superb artwork by Martí Franch, which can be viewed at high resolution on the British Birds website.