Northern Saw-whet Owl (Aegolius acadicus)

Under UV light, newly molted feathers glow pink while older feathers glow white. This technique can be used to study molt patterns, feather wear, and to ascertain age. All of this individual's flight feathers are new, indicating this bird hatched this year. Bird banders would designate this an "HY" (Hatch Year) bird.

The ten outermost flight (long) feathers are the primaries, numbered P10 through P1 starting from the outer edge. The inner set of long feathers are the secondaries, numbered S1 through S10 where S10 is closest to the body. Thus, P1 and S1 are adjacent.

Second Year saw-whets (birds about a year old and designated SY by banders) have molted their outermost primaries and innermost secondaries. This bird has old P4 - P1 and old S1 - S5 as indicated by the whiter color.

Birds older than 2 years show more complex molt patterns.