Atlantic Puffin: subspecies and ageing

Bill development

During the first five years of its life the bill of the Atlantic Puffin develops rather slowly to maturity. First winter birds have small bills which don't show yet the distinctive colors and vertical grooves in the orange tip. These appear in the following years. The bill becomes deeper with age and gets up to 3 grooves. The number of grooves provide a good - though not exact - indication of age until it starts to breed at the average age of five to six years. Harris (1976) investigated this phenomenon at the Isle of May breeding grounds, where 21 individuals were recaptured during several years. It was found that most two year old birds had 1 groove, three year old birds mostly 1,5 (1-2) grooves, four year olds mostly 2 (1,75 -  2+)* grooves, five year olds 2 - 3 grooves, 6 year olds 2+ - 3), seven year olds 2+ - 3. Old birds with three grooves may show a chalky substance in the third groove. But breeding birds with no grooves at all occur and a few will never get more than 2 grooves.

Puffins have summer and winter bills because they molt the ramphotecal coating every year. After the breeding season the bill starts to flake off. Winter bills are less deep as in summer, due to the shrinking of the cere and a less deep 'chin'. The grooves are still present in winter bills, but less distinct.

* 2+ = 2 grooves + 1 suggestion of a groove

Atlantic Puffin Fratercula arctica grabae 2
Horta, Faial, Azores (ring: Lisboa J 02470)
Culmen: 39.2 mm; # grooves: 0 Total: 78.6, 1st winter
(ca 9 months), 2nd cy, juvenile

Atlantic Puffin Fratercula arctica grabae 1
Belgium, february (Tricolor oil spill, 2003)
Culmen: 41.6 mm; # grooves: 1 shallow Total: 78.6 mm,
2nd winter, 3rd cy, immature female

Atlantic Puffin Fratercula arctica grabae 1
Belgium, winter (Tricolor oil spill, 2003)
Culmen: 44.7 mm; # grooves: 2
Total: 81.9 mm, adult male. 1

Atlantic Puffin Fratercula arctica
Culmen: 45.3 mm, depth: 35.7 mm, # grooves: 1,5
Total: 81.6 mm; unsexed adult, summer

Atlantic Puffin Fratercula arctica
Location unknown
Culmen: 46.0 mm, Depth: 34.0 mm, # grooves: 2,5
Total: 80.3 mm, unsexed adult, summer

Bill measurements

The bills of the three subspecies differ in size depending of their sex, origin and season. Northerly birds of the subspecies naumanii have substantially larger bills than those of grabae originating from the British Channel area, the southern end of their distribution.  There are also differences in (bill-) measurements in birds from different localities and males average larger.  Isle of May puffins for instance have larger bills than from most other British colonies (Harris, 1976). Puffins from southern Iceland are smaller and seem more close to grabae, than birds from the northern parts of this island which are more like arctica  (Petersen, 1976).

The increase in size of Atlantic Puffins is clinal from south to north. East - west differences have also been found.

Several authors have proposed to discard the recognition of subspecies and to consider Atlantic Puffins conforming to a cline (Petersen, 1976). In all cases there is an overlap in bill measurements (see table below). Only at the bottom and top end of the range measurements might provide a reliable subspecific identification in beachcast birds outside the vicinity of their breeding locality. Winter bills are less deep

Bill measurements of adult Atlantic Puffins (summer)
Subspecies  sex                Bill length      Bill depth (mm)

naumanni *  ♂
naumanni *  ♀

41 - 51
38 - 48
41 - 52
40 - 50
45 - 47
43 - 60

41 - 41
27 - 38
35 - 42
32 - 40
35 - 48
35 - 49

*measurements include cere (horny rim at the base of the bill) After Camphuysen (pers. notes)

Skull development

Skull development in Puffins follows the same pattern as in other auks. In its first winter the different bones of the skull have not fused yet. Fusion will be more or less complete in spring of its second calendar year. Puffin skulls don't develop the supraorbital ridge like Alca, Uria and Alle.

1. Courtesy of Kees Camphuysen, NIOZ (Royal Netherlands Institute for Sea Research)
2. Courtesy of Joel Bried, Dep. of Oceanography and Fisheries, University of the Azores, Horta, Faial.