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NORTHERN SAW-WHET OWL
Aegolius acadicus

Northern Saw-whet Owl

All text & photos © Hilton Pond Center

Hatch-year Northern Saw-whet Owl (above)


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(updated 4 Dec 2011)

In 1999, Hilton Pond Center for Piedmont Natural History became what was then the southernmost site in a national network using night-time banding to study dispersal of Northern Saw-whet Owls, Aegolius acadicus. This northern species breeds primarily in the northeastern and western U.S. and in southern Canada (green area on map below right) and overwinters mainly in the central U.S. and the Atlantic Coast states (blue area on map). As banding studies have expanded, winter banding records for these owls have increased for several southern states, including Alabama, Georgia, and South Carolina.

Through October 1999, only four Northern Saw-whet Owls (NSWO) had ever been banded within South Carolina--the first in 1960 and the latest in 1972; none had ever been banded in South Carolina's Piedmont region. At Hilton Pond Center in November and December 1999, Bill Hilton Jr. netted and banded seven of these diminutive owls that perhaps migrated in from Canadian forests but may have come from a population that breeds in the southern Appalachians of North Carolina.

NSWOs are captured by playing an audiolure (endless-loop recording) of the owl's monotonous "toot-toot-toot" call from shortly after dusk until just before dawn at high volume. Owls are attracted to the sound and--as they approach the tape deck's speakers--fly into an array of 60mm-mesh mist nets that are 12 meters long and 2.6 meters tall; thus far we have used a triangle of nets with the speaker in the middle and with a fourth net extending from one of the triangle apices. Nets, checked hourly through the night, are not deployed during wet weather or when temperatures are below 25 degrees F.

Although Northern Saw-whet Owls are sexually monomorphic (i.e., males and females look alike), there is measurable size difference between the sexes; females generally are about a third larger than males. Researchers elsewhere have determined saw-whets can be sexed with greater than 90% accuracy by comparing an individual owl's wing chord and mass. Ageing is facilitated by looking at the owl's wing under ultraviolet light; newer feathers glow pink under UV because of porphyrins (see below), so a young saw-whet's wing will be uniformly pink because all its feathers came in at once. Adults exhibit partial molt, so some of their older feathers may not show any pink color at all.

All text & photos © Hilton Pond Center

10 NORTHERN SAW-WHET OWLS BANDED
AT HILTON POND CENTER
1999-2007

BAND
NUMBER

CAPTURE
DATE

AGE

SEX
(based on measures)

WING
CHORD (mm)

MASS
(grams)

0554-13207

11/29/99

Second Year

Female

137

98.4

1333-92472

11/29/99

Hatch Year

Unknown

134

85.7

1333-92473

11/30/99

Hatch Year

Female

135.5

99.3

1333-92474

11/30/99

Hatch Year

Female

130.5

89.8

1333-92475

12/02/99

Hatch Year

Unknown

138

85.0

1333-92477

12/05/99

Hatch Year

Male

132

78.1

1333-92478

12/08/99

Hatch Year

Female

137

90.8

0554-13208

11/30/00

After Hatch Year

Female

137

105.3

0554-13209

11/27/01

Second Year

Female

137

104.5

0554-13211
12/15/07
Hatch Year

Female

142

97.4

All text, tables & photos © Hilton Pond Center

After our initial seven bandings in November and early December 1999, 13 additional nights of playing the audiolure in mid- and late-December 1999 and early January 2000 did not result in the capture of any new or banded Northern Saw-whet Owls at Hilton Pond Center. It is suspected that overwintering saw-whets leave the South Carolina Piedmont at latest by mid-March, when they are known to start showing up in good numbers at more northerly migration banding sites.

In the fall of 2000, an audiolure was played dusk to dawn at Hilton Pond Center starting on 31 October--about a month earlier than in 1999--to determine when NSWOs actually begin to arrive in the Piedmont. The first capture came on the night of 30 November (see table above)--a year and one day after the first local bandings for this species. Six additional nights of netting resulted in no other owls. In 2001, the first and only capture came on 27 November, just a few days earlier than the earliest local record. In 2007, no NSWO were captured on the evening of 5-6 December; the next net night was 14-15 December when we finally netted our tenth NSWO.

NOTE 1: Netting attempts on three nights in early December 2004 produced no owls. No netting attempts were made in the winter of 2002-2003 because of knee surgery on the owl bander, or in most winters since because of bander illness, eye surgeries, finances, work obligations, or extended travel.

NOTE 2: One gray-brown-morph Eastern Screech-Owl, Otus asio (left)--itself apparently attracted by the NSWO tape--was caught in a net on 5 December 1999.

NOTE 3: In 2011 we began playing the audiolure and running night nets on 4 December, with plans to continue almost nightly at least through the middle of the month. (A recent influx of Coyotes around Hilton Pond Center may affect our plans.)

Click here for information about Other South Carolina Bandings of Northern Saw-whet Owls.

 


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