Aegolius funereus - autumn

Boreal Owl / Pärluggla

AGE - BEST CRITERIA:

In 1cy, all PP and SS are uniformly juvenile lacking moult contrasts. In older age classes the moult wave works through the hand (inwards) and the arm (outwards) according to the description below.
 
1cy: 
  • Uniformly juvenile PP and SS, lacking moult contrasts. The feathers are often rather narrow and worn.
2cy:
  • PP and SS show two distinctly different generations. In most birds, outer 2-6 PP and inner 2-5 SS (and tertials) were moulted during the summer (first post-breeding). These are fresh, darker and slightly broader compared to the rest of the wing that is pale, worn, juvenile. In birds where it's uncertain whether two or three generations are present in the wing, 2cy+ should be used.
3cy:
  • PP and SS show three generations of feathers. 2-5 recently moulted (second post-breeding) feathers are found in the central parts of the hand and arm, while fearthers of intermediate wear (first post-breeding) are found in the outer hand and inner arm, and lastly, worn juvenile feathers in the inner hand and outer arm. In some birds, with three generations present in the wing, but it's unclear whether one of them is juvenile or not, 3cy+ should be used.
4cy+:
  • Birds that show recently moulted (third post-preeding) inner PP and outer SS as well as a new wave starting in the outermost PP should safely be regarded as 4cy+. However, note that Hörnfeldt et al. (1988) states that many 4cy still retain juvenile innermost P10 (and, hence, may show four different generations of PP). In a few birds (probably 5cy+) this second wave is more advanced (central or inner part of the hand), but the age class 5cy+ should probably best be regarded as tentative.
 
1cy October. Typical first year bird showing a uniform and evenly coloured wing without any moult contrasts. The degree of wear differ a bit between individuals. [7133161]
1cy October, showing variation. Note that some individuals are less worn, and also that the white spotting may vary individually in size and intensity. [7133189]
2cy October. Two different generations of PP and SS are present in the wing. PP1-4, SS8-10 and the tertials are first post-breeding and the rest are juvenile. Note that the PC are moulted together with its respective P. [7133177]
2cy October. Another 2cy showing the same extent of moult as the previous one. Note variation in the white spotting as well as in wear. [7133181]
3cy October. A rather typical bird showing three generations of SS and PP in the wing. PP1-4 are first post-breeding (intermediate wear), PP5-6 are second post-breeding (fresh) and PP7-10 are juvenile (worn). SS1-4 are juvenile, SS5-6 are second post-breeding and the rest are first post-breeding. [7133163]
3cy October, showing variation and irregular sequence in the moult. PP1-4 are first post-breeding (intermediate wear), PP5-7 are second post-breeding (fresh) and PP8-10 are juvenile (worn). S1 and S4 are juvenile, SS2-3 and SS5-6 are second post-breeding and the rest are first post-breeding. [7133174]
4cy+ October. Recently moulted PP8-9 as well as (a new wave) PP1-3. This state of moult is typical for 4cy, and the retained innermost P10 seem juvenile (much worn and rather narrow), giving further confidens to the age being 4cy (rather than 4cy+). But in older age classes, similar patterns will reappear with an interval of a few years, and if the innermost P10 is not juvenile (but instead a retained worn feather from an adult generation) the wing would be very difficult to separate from the one shown here. For this reason, we find it advisable not to go further than 4cy+ in birds looing like this. [7133087]
5cy+ October. Some fully adult birds that show a complex pattern of moult waves that is more advanced than expected in a 4cy bird may tentatively be called 5cy+. However, since individual variation in wear and moult is a true pitfall, it's important to acknowledge a certain insecurity to this age class. [7133107]
More Aegploius funereus:
Moult
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