Hatching Year

Northern Saw-whet Owls chicks that are still in the nest are assigned the Bird Banding Lab age class L (local), but once they fledge and leave the nest, through 31 December of that year, they are assigned the age class HY (hatching year). In southern latitudes some saw-whet owls fledge as early as  late March or early April, while in the bulk of the species’ breeding range fledging occurs in June or July.

Nestling owlet, near fledging age, in juvenal plumage (© David F. Brinker)

Northern Saw-whet Owl during first prebasic molt between juvenal and basic plumages (© David F. Brinker)

During its first three or four months,  a young Northern Saw-whet Owl wears two distinctly different plumages.  Its first plumage, acquired in the nest cavity, is the fulvous-and-chocolate-colored juvenal plumage illustrated in most field guides.

The juvenal plumage is worn until the first prebasic molt takes place in August or, at latest, early September.  In rare cases, likely with unusually late broods, this molt may extend beyond September.  During the prebasic molt the body contour feathers are replaced so that the young owl is now difficult to distinguish from older Northern Saw-whet Owls in the field.  During the first prebasic molt the rectices, primaries and secondaries are not replaced.  Thus autumn migrant hatching-year Northern Saw-whet Owls have flight feathers that do not show the contrasts in color associated with older owls.  All flight feathers on HY saw-whet owls are uniform in color and are normally dark with fresh, unworn margins.

Fall hatching-year wing in white light (top) and long-wave ultraviolet (bottom). Note even fluorescence across all flight feathers. (©Scott Weidensaul)

When viewed under UV light, HY saw-whet owls captured in fall migration show an even fluorescence across the underwing surfaces, most intense in the inner primaries and outer secondaries, and fading significantly across the innermost secondaries, which show little or no fluorescence.  Banders generally do not complete molt cards for HY Northern Saw-whet Owls because all flight feathers are of the same molt generation.  HY saw-whet owls in their first basic plumage are encountered from late August until 31 December.

Dorsal surface of an HY Northern Saw-whet Owl wing in natural early morning light. (© David F. Brinker)