Atlantic Puffins Fratercula arctica in summer and winter plumage can be aged as first-year, second-year, third-year, young adult and old adult using the number of grooves on the outer part of the beak. The technique is useful to bird ringers and those dealing with birds found dead in wrecks and pollution incidents where knowledge of the ages of individuals involved can help assess the likely effect on breeding populations.

Although wrecks of seabirds after spells of severe weather occur periodically, they generally do not involve Atlantic Puffins Fratercula arctica. However, in March 2013 c. 4,500 dead Atlantic Puffins (hereafter ‘Puffins’) were washed up on the beaches of east Scotland and northeast England, and in February 2014 c. 30,000 dead and dying Puffins were counted on the shores of the Bay of Biscay, France, Portugal and southern Britain (Harris & Elkins 2013; Farque 2014; Turner 2014; H. Jessop/RSPB pers. comm.). These are among the largest wrecks of Puffins recorded and they could potentially have a serious effect on the numbers of Puffins around Britain and elsewhere, especially if mainly breeding adults were affected. Aging of Puffins during the summer using morphometric criteria is well documented (Petersen 1976; Harris 1981), but these wrecks drew attention to the lack of information on how to age Puffins during the winter (but see Camphuysen et al. 2007; Harris & Wanless 2011). This paper aims to fill this gap by bringing together images of Puffins in the summer and winter to highlight the key criteria used for aging throughout the year and provide a detailed description of the changes in the bill that occur during the non-breeding season.

The Puffin is immediately identifiable throughout the year due to its contrasting black-and-white plumage and more importantly the strikingly enlarged and colourful beak. However, it takes several years for an individual to reach this state (details in Petersen 1976; Harris 1981). During the first 4-5 years of life the wing length increases, the bird becomes heavier and the beak becomes deeper with the profile changing from triangular to extremely convex. As the area of the beak increases, grooves develop in the outer part, the number of which gives an indication of the age of the bird. The rate of development of the beak varies among individuals but, despite it not being possible to age any individual with 100% certainty, it is possible to classify most individuals as being in their first, second or third year of life, as a young adult (probably in its fourth or fifth year) or an old adult. The significance of the number of grooves has not been demonstrated but as Puffins do not normally breed until they have at least two bill grooves and the bill is used in display, they presumably have some sexual importance.

I thank the very many people who have collected and photographed dead Puffins for me over four decades but particularly Debbie Russell, Mel Froude, Martin Heubeck, Stuart Murray, Mark Newell, Eric Meek, Catrina Barrett, Jens-Kjeld Jensen, Dan Turner and members of the Northeast England Beached Bird Surveys Group, and Alastair Duncan and other members of the Grampian Ringing Group. Sarah Wanless, Martin Heubeck and Kees Camphuysen greatly improved the manuscript with their comments.

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