SHORT COMMUNICATIONS 
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fig. I. Paired views of ventral surfaces of Northern Saw-whet Owl wings, photographed in October-November under 
visible light and ultraviolet light. Hatching-year (A) showing even fluorescence across all underwing surfaces; second-year 
'Bi showing contrast between strong fluorescence on newly molted outermost primaries and innermost secondaries ana 
after-second-year (C) showing three generations of feathers, including chalky-white retained juvenal primaries _ wi no 
fluorescence. Photographs by Scott Weidensaul. 
secondaries 8—12; DFB, unpubl. data), show a 
distinctive pattern of bright fluorescence in these 
areas, separated by a block of older retained 
juvenal feathers with relatively little fluorescence, 
limited to the base of the flight feathers (Fig. 1B). 
Owls showing a mix of old and new feathers, but 
not in the sequential block pattern ot a SY 
• Fig. 1C), are classified as after-second-year 
<ASY). after Pyle (1997). 
Extremely old feathers, presumably those at 
least 2 years of age, appear chalky or yellowish 
white under black UV light, evidencing no sign of 
fluorescence. Distinguishing third-generation 
feathers from second-generation feathers can be 
challenging, requiring significant experience on 
the part of the bander, particularly when working 
under artificial light at night. However, the 
difference under UV light is usually easily 
apparent, even to relatively inexperienced work¬ 
ers. Thus, use of UV light greatly improves the 
accuracy of age classification of Northern Saw- 
whet Owls. 
