Saw-Whet Research

Since 1997, the Ned Smith Center has been a leader in saw-whet owl research in Pennsylvania, and more recently continent-wide. Until the center began its work, no one even realized saw-whets migrated through Pennsylvania in large numbers.

Every autumn the center operates three fulltime banding stations (in Schuylkill, Dauphin and Cumberland counties), which are open seven nights a week from the beginning of October through late November or early December.

As many as 900 owls a season are netted, banded, weighed and measured before being released. The stations are operated by a team of 18 federally licensed banders, with help from a crew of more than 85 trained volunteers. Each site is open from dusk until about midnight, weather permitting, and as many as 40 owls a night may be netted in one location.

The banders use a line of very fine, soft mist nets stretched through the woods, with a digital recording of the male saw-whet’s “toot” call playing at high volume near the nets. Passing owls are attracted by the call and caught in the nets, which are checked regularly through the night.

Once captured, each saw-whet is fitted with a lightweight, numbered leg band issued by the federal Bird Banding Lab, its age and sex are determined, it is weighed and a variety of measurements are taken, all of which help scientists learn more about these secretive birds. Sometimes a feather or tiny blood sample is taken for DNA research, or to help disease specialists studying the spread of ailments like West Nile virus or Lyme disease. Each fall, a few owls are fitted with minute radio transmitters barely as large as a pencil eraser, which help us more closely track their movements.

Then the owl is released – and if it is ever captured again by another researcher, or found dead by the general public, the serial number on its band will help us learn more about the movements, lifespan and ecology of these owls. Each year, many of the owls captured by the NSCNA crew have already been banded by other researchers, and many of the owls we band are subsequently reported. To learn more about these recoveries, and what they tell us about saw-whet owls, click here.

Bird Banding

Each year, about 1.2 million birds are banded in North America with light, aluminum alloy leg bands, each stamped with a unique serial number and issued by the federal Bird Banding Laboratory in Laurel, Maryland. (The Canadian banding program is managed by the Canadian Wildlife Service in cooperation with the BBL.)

Captured owls are ringed with a lightweight aluminum alloy band stamped with a unique serial number, which remains on the bird for life.

Once the bird is banded, the basic information – species, age, sex, date, location of banding – is entered into the Banding Lab’s database. If the bird is ever encountered again, either recaptured by another bander, killed by a hunter (in the case of gamebirds) or found dead, and the number reported, the finder will receive a certificate of appreciation detailing the bird’s history, and the bander likewise is notified.

Check out our video page to see Scott Weidensaul explain how banding saw-whets helps protect their habitats.

To report a banded wild bird (not including pigeons), call 1-800-327-BAND, or go to http://www.reportband.gov

Ageing and Sexing Owls

The wing of a hatching-year (first fall) owl shows no contrast, with all feathers glossy, new and unfaded. By the next autumn, as a second-year bird, the owl has replaced its outermost and innermost flight feathers, which contrast with the older, faded retained feathers in the middle of the wing.

Like all banders, saw-whet researchers must infer the age of the owls they catch by examining the molt, or replacement pattern of the birds’ feathers, especially those in the wings. In owls, complete molt is a process that can take up to four years.

A saw-whet with flight feathers that are all bright, glossy and unworn is an owl that was just born the previous spring – an HY, or hatching-year, bird, in bander jargon. By the following fall, an SY (second-year) owl will have replaced its outermost and innermost wing feathers, with the old, retained juvenal feathers in the middle of the wing now faded and worn. Older birds may have as many as three generations of feathers.

A pigment in owl feathers called porphyrin fluoresces under ultraviolet light, and because it fades quickly with time, the degree of glow gives banders a handy way to age feathers. This adult saw-whet shows a mix of old (faded) and new (brightly fluorescing) feathers.

But owl researchers have one additional tool – a black light. Unlike most groups of birds, owls have a pigment in their feathers known as  porphyrin, which under ultraviolet (black) light fluoresces a brilliant neon raspberry. Because porphyrins degrade quickly from exposure to sunlight, older feathers become paler and duller, while newly molted feathers glow brightly, giving banders a handy way of reading the age of the feathers – and thus determining the age of the owl.

In any light, male and female saw-whet owls look identical, but there is a subtle difference – females average significantly larger than males, weighing up to 100 grams, compared with 75g or less for most males. Banders use a combination of the owl’s weight and the length of its folded wing (known as the wing chord) to determine the owl’s gender, but about 15 percent nevertheless fall into the “unknown” category

Tracking Saw-Whets by Radio

Smaller than a pencil eraser and weighing less than 2 grams, tiny radio transmitters allow the center’s researchers to follow the movements of saw-whet owls.

Since 2001, the center’s research crew has used miniature radio transmitters to learn more about saw-whet owl migration and ecology.

The transmitters, which are about the size of a pencil eraser and weigh less than 2 grams (less than 1/14th of an ounce), are attached with a backpack harness made of thin, elastic nylon cord designed to fall off after several months, and allow the research crew to track the owls’ movements.

Because the radio transmitters must be small and lightweight, they do not have a great range in the mountainous terrain in which the crew works, so they do not attempt to track the owls when they are actively migrating. Instead, their primary focus is on what ornithologists call “stopover,” the resting period between active migration bouts. Saw-whet owls are unusual in that their stopover periods can last days or even weeks, allowing the research crew to find the owls on their daytime roosts and assess the habitats they are using.

Using handheld receivers and directional antennas, the tracking crew can take a bearing on the owl’s position – and by fielding two or three teams of trackers at night, the crew can triangulate the position of a hunting owl, allowing them to map the nightly activity ranges of the saw-whets, something about which little is known.

Most of the owls we have radio-tracked were captured at our King’s Gap site in Cumberland County, and tracked through the surrounding Michaux State Forest. Some remained in the area for many weeks, shifting their daily roosts unpredictably.

Some of Our Favorite Owls…

“Glenda”

Band #0924-00980
Hatching-year female, banded at King’s Gap Oct. 22, 2004
Tracked Oct. 24-Nov. 26, 2004; she dropped her radio Nov. 27, 2004.

Glenda used a variety of roost sites, ranging from chestnut oaks and red oaks to pitch pine, white pine and mountain laurel, perching just a few feet off the ground in the latter. She stayed in the southeast corner of the King’s Gap Environmental Education Training Center, close to the Buck Ridge Trail, and along nearby Cold Springs Road in Michaux State Forest.

“Squash”

Band #0924-01072
Second-year female, banded King’s Gap Nov. 18, 2004
Tracked Nov. 18-Dec. 22, 2004

Squash and Glenda were both using the same small area of King’s Gap and Michaux State forest, between the Buck Ridge Trail and Cold Springs Road.

Like many of the saw-whet owls we tracked, Squash showed a distinct preference for pitch pines when it came to choosing a daytime roost. These tall, scraggly conifers are considered a junk tree by many foresters, but our research suggests they are important to saw-whet owls in the predominantly oak woodlands of Michaux State Forest. The only non-pitch pine Squash used was a Norway spruce on Dec. 2, almost in someone’s backyard.

Why pitch pines? Perhaps because they are widely distributed along the ridgetops throughout the state forest – and perhaps because their branches are filled with cones not much smaller than a saw-whet, making it very difficult to spot a roosting owl.

“Chunky”

Band #0924-27996
After-second-year female, banded King’s Gap Nov. 13, 2007
Tracked Nov. 19-Dec. 12, 2007

After banding, Chunky (named for her size) moved southeast of King’s Gap, and set up shop along Mountain Creek near Hunters Run Road. Unlike many of the tagged saw-whets, she seemed to prefer white pines as her daytime roost, sometimes picking trees with very sparse needles that made her easy to spot. However, she was at least three years old at the time, and had obviously learned how to avoid danger.

Several times, the tracking crews observed Chunky holding deer mice that she’d killed the night before, partially eaten, and would finish off in the evening before going hunting again. An adult saw-whet will usually eat about two mice per night.

“Grinch”

Band # 0924-28022
Second-year female, banded King’s Gap Nov. 17, 2007
Tracked Dec. 4, 2007-Feb. 2, 2008

The Grinch was tracked longer than any of the other 22 owls tagged since 2001, providing a wealth of information about saw-whet roost habits and habitat selection – including this species’ fondness for pitch pines. Of the 32 roost sites we confirmed, 31 of them were in pitch pines (the sole exception was a white pine).

After banding, the Grinch moved just west of King’s Gap into Irish Gap Hollow, where the northwest slopes of the hills were thickly clad in conifers. After spending 17 nights there, shifting from tree to tree on occasion, she moved 3.2 miles to the southwest to Beetem Hollow in Michaux State Forest, where she remained except for one quick excursion close to Route 233 for a single day, Jan. 12, 2008, before returning to Beetem Hollow.

(Right: Aura Stauffer, telemetry project coordinator, takes data on a roost tree while the Grinch watches from a few feet above her head. ©Jamie Flickinger

Where are the Guys?

One of the biggest mysteries about saw-whet owl migration is the scarcity of male saw-whets, which make up just 6 percent of the owls the NSCNA research team captures. So where are the guys?

One possibility is that the audiolure the team uses – the tooting call of a male saw-whet – is simply more attractive to female owls, even though autumn is not the breeding season. But researchers in other areas, who used nets but no audiolure, also reported that they caught more females than males. It appears the lure is only part of the story.

One possibility is that adult male saw-whets stay on their breeding grounds year-round, leaving migration to females and young owls. If so, this would be a very unusual migration strategy among raptors, but there is some evidence for it. Almost all the males captured at the center’s banding stations are first-year owls, too young to breed – out of nearly 4,500 owls banded since 1997, only 40 have been adult males.

Notable Recoveries

A map showing the points of origin for some of the more than 160 owls originally banded elsewhere and recaptured at the NSCNA banding stations.

By marking a wild bird with a numbered leg band, scientists can uncover many of the remaining mysteries about their lives – where they travel, whether they return to the same places each summer and winter, whether they choose the same mates, and how long they live, among many other things.

Each year, the NSCNA crew catches saw-whet owls (known as foreign recaps or foreign recoveries) that have already been banded by other researchers, and some of the owls they in turn band and release are encountered weeks, months or years later, sometimes hundreds of miles away. Here’s a small sample:

Foreign owls:
Among the more than 160 owls banded elsewhere that the NSCNA crew has recaptured were birds originally:
–Banded Oct. 4, 1998 at Cabot Head (Bruce Peninsula) Ontario; recaptured Oct. 31, 2001 at Hidden Valley.
–Banded Oct. 29, 2001 at Bancroft, WI; recaptured Oct. 29, 2003 at Small Valley.
–Banded April 27, 2003 at Bois Blanc Island, MI; recaptured Nov. 6, 2004 at Small Valley.
–Banded Oct. 13, 2003 at Plover, WI; recaptured Nov. 11, 2005 at Hidden Valley.
–Banded Sept. 21, 2004 at Falmouth, ME; recaptured Oct. 25, 2004 at Small Valley, a distance of 403 miles.
–Banded Sept. 29, 2004 at Earlton, Ontario; recaptured Oct. 24, 2005 at Small Valley.
–Banded Oct. 4, 2004 at Cedar Grove, WI; recaptured Nov. 5, 2005 at Small Valley.
–Banded Oct. 10, 2005 at Eels Lake, Ontario; recaptured Nov. 19, 2005 at Hidden Valley, a distance of 300 miles.
–Banded Oct. 9, 2006 at Whitefish Point, MI; recaptured Oct. 12, 2007 at Hidden Valley.
–Banded July 30, 2007 as a juvenile, Whitefish Point, MI; recaptured Oct. 7, 2007 at Hidden Valley, a distance of 609 miles.
–Banded Sept. 18, 2007 in Tadoussac, Quebec; recaptured March 28, 2008 at King’s Gap.

NSCNA Birds Elsewhere
Among the more than 100 owls banded by the NSCNA crew, and reported elsewhere, were birds originally:
–Banded Oct. 10, 2001 at Berry Mountain; recaptured Oct. 8, 2002 at North Yarmouth, ME.
–Banded Nov. 11, 2001 at Berry Mountain; recaptured Snake Mountain, VT, Oct. 14, 2002.
–Banded Nov. 11, 2001 at King’s Gap; recaptured Nov. 14, 1002 at Hopkins Forest, MA.
–Banded at King’s Gap Oct. 23, 2003; recaptured Oct. 21, 2005 at Sand Bluff, IL.
–Banded Nov. 18, 2005 at Small Valley; recaptured Oct. 14, 2006 at Tadoussac, Quebec.

The total also includes 16 owls recaptured over the years at Lamb’s Knoll, MD, in the Catoctin Mountains 50 miles south of King’s Gap; 14 owls recaptured at Waupoos Island/Prince Edward Point, Ontario, on the northeast shore of Lake Ontario; and seven owls recaptured on the Delmarva Peninsula from Assateague Island, MD, to Kiptopeke, VA.

Project Owlnet

Project Owlnet is a collaborative undertaking involving nearly 120 owl research stations across the U.S. and Canada, all working to better understand the movements and ecology of saw-whets and other migratory owls.

Owlnet was founded by David Brinker of Maryland’s Department of Natural Resources, and is coordinated by Brinker, Steve Huy of Maryland and NSCNA saw-whet project leader Scott Weidensaul.

The Owlnet website provides standard methodologies, techniques and approaches for scientists interested in conducting migration research, as well as an active listserve to allow participants to share their results, data and information on band recoveries.

Ned Smith Center