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Birds of Prey

A Feathered Visitor

For the past six winters a Barred Owl has been a daily visitor at my house.  For most of these years, he roosted (and slept) all day every day from December through February on a White Birch tree just outside my door.  Although I usually try not to interfere with the natural rhythm of things, one year when the snow was exceptionally deep, making hunting quite challenging, I decided to offer the owl a daily treat – one small rodent.  Enough to entice him but not to satiate him or make him dependent upon this source of food. (I once opened up the gizzard of a road-killed Barred Owl and discovered five small rodents – they average about this amount per day.) Thanks to the Listserv in my town, I could appeal to residents for small rodents (trapped, not poisoned) which they generously deposited in a specially marked box outside the Town Hall, freshly frozen.

 

Every afternoon like clockwork the Barred Owl would become alert and open his eyes.  If he had left his perch during the day, he would return at dusk, precisely at 4:30 p.m. His timing appeared to be in sync with the amount of daylight, as he arrived a bit later as the days lengthened.  Most mornings I would take a mouse from the freezer and let it thaw (when I forgot, the microwave came in handy!).  I would take the mouse outside, dangle it by its tail to alert the observing owl, and place it on the railing of my porch. Practically before my hand released the mouse the owl would fly in, grasp the mouse on the fly in its talons and disappear into the woods. More than once I felt the tips of his wings brush against me.

Six years, 60 days a year, comes to 360 days…this owl has spent nearly a year, one-tenth of its life, outside my door.  I came upon the remains of a Barred Owl not even a quarter of a mile from my house this week.  I can only hope it wasn’t my friend.

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Snowy Owls Starting Their Return To The Arctic

Every year in North America some Snowy Owls migrate southward during Arctic winters while some remain in the Arctic.  (In some winters — not this one — we see large numbers, or irruptions, of young owls in the Northeast which is thought to be a result of food and weather conditions further north.)  Individuals that spend the winter in New England usually can be found near large, open terrain that resembles their Arctic breeding grounds. Agricultural fields, coastal dunes and airports provide them with an ample diet of small mammals and birds.  Overwintering Snowy Owls begin to head northward in March and April. Occasionally a few owls linger on wintering grounds well into spring and summer (records of Snowy Owls exist in May in Massachusetts and June in New Hampshire).

Much has been learned about the migratory flights of Snowy Owls due to satellite tracking. According to Birds of North America, in February 2012, a transmitter attached to a female at Logan Airport in Boston, MA tracked an owl to Nunavut, Canada. The owl migrated north along Hudson Bay’s eastern shore during spring migration and returned south along Hudson Bay’s western shore during the autumn migration. It eventually returned to Logan Airport the following November, having completed a 7,000 mile round trip.

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Great Horned Owls Courting & Mating

Great Horned Owls are one of the earliest species of birds to breed in the Northeast. Their intense hooting begins in late December or early January, about a month before actual mating takes place. Males call during most seasons of the year, but the period when the males are hooting vigorously lasts for a month or six weeks. During the mating season the deep, rich tones of the males are occasionally interspersed with the higher and huskier notes of the females. The answering calls of the females are typically heard for only a week or two, toward the end of the six-week period.

Eventually, when a male and female approach each other, they do a sort of courtship “dance.” The male cocks his tail, swells his white bib (see photo), and with much bobbing and jerking utters a series of deep sonorous calls that elicit calling responses by the female. He cautiously approaches the female, continuing much tail-bobbing and posturing. The owls nod, bow, and spread their wings as well as shake their heads. Courting pairs have been observed engaging in high-pitched giggling, screaming, and bill-snapping. Mutual bill rubbing and preening also occurs. Copulation concludes the courtship ritual, with both owls hooting at a rate of 4 or 5 hoots per second throughout copulation, which lasts 4 – 7 seconds.

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Great Horned Owl Nestlings About To Fledge

5-17-19 great horned owls_U1A8938Great Horned Owls do not build their own nests, though they may provide some lining to an existing cavity or nest. Snags, cliffs and man-made structures provide nesting sites, but most commonly Great Horned Owls use the tree nests of other species such as hawks (especially Red-tailed) crows, ravens and squirrels. Most, but not all, nests are used for only one season. Pictured is a Great Blue Heron nest that has been usurped by a Great Horned Owl family – a feat achieved by the owls claiming the nest as early as February, prior to the return of herons.

After incubating her eggs for roughly a month, the female Great Horned Owl then broods her young for two to three weeks. The father’s role consists of bringing food to the female while she is incubating and brooding. She then tears the food up into bite-size pieces for the nestlings.

When the nestlings no longer need the heat their mother’s body provides, brooding ends but the mother stays with her nestlings until they fledge at about seven weeks of age. (Pictured: Great Horned Owl mother and two downy nestlings, roughly six weeks old. Thanks to Marc Beerman for photo op.)

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Hungry Barred Owls Near Feeders

3-4-19 barred owl _U1A2992Over the past few weeks many people in northern New England have discovered Barred Owls perching near their bird feeders during the day. At this time of year, with snow on the ground, food is harder to find and owls are forced to hunt during the day as well as at night. Bird feeders are a sure source of food, as mice and voles are coming out to feed on spilled seed (most often at night).

The owls we see are relying primarily on their sense of hearing to locate small rodents. Their ear openings are asymmetrically placed, which means that sounds reach the owl’s ears at different times. This helps them zero in on the exact location where the sound is coming from, both when they are perched as well as in flight.

Although Barred Owls can detect the sound of a mouse scurrying through tunnels two feet beneath the snow, this winter has been more challenging for them than many. Almost every snow storm has been followed by rain, which has created multiple layers of icy crust. Although sound may be heard through solid, liquid, or gaseous matter, one wonders if these multiple layers of crust compromise an owl’s ability to hear. In addition, these conditions can’t help but impede an owl’s ability to reach its target as quickly as it normally does.

A dear friend whose compassion for creatures big and small is unmatched was going to great lengths (coating balls of hamburger with hair cut from her dog’s coat so they would bear some resemblance to small rodents) to help a resident owl in a time of need. Some would argue that nature shouldn’t be interfered with, but those readers with a desire to come to the aid of a hungry owl could let a little seed fall on the snow that’s packed down around the feeder in hopes that a large supply of accessible food might attract more rodents which might fill more owl stomachs.

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An Owl’s Digestion Process

11-26-18 -barred owl coughing up pellet2 _U1A1839Most owls do not bother to tear small prey such as mice and voles apart but instead swallow them whole.  After eight to sixteen hours, all the nutrients available in the eaten prey have been absorbed by the bird.  Owls cannot digest the fur, feathers, bones, teeth and nails of their prey, so these parts remain in the bird’s gizzard (specialized organ that grinds up food in most birds but serves as a filter for holding indigestible parts in birds of prey).  This accumulation of indigestible parts takes on its pellet form (which is the shape of the gizzard) about eight hours after ingestion, but is sometimes retained by the owl for another six hours or so before being coughed up. As a rule, bones are on the inside of the pellet, and the fur and feathers form a soft coating on the outside.

The stored pellet partially blocks the entrance to the digestive system so it must be ejected before the owl can eat again.  This process takes anywhere from a few seconds to several minutes.  The owl appears to “yawn” several times before regurgitating the pellet.  Note that the pictured Barred Owl has prey (a Deer or White-footed Mouse) in its talons, but out of necessity is getting rid of a pellet before devouring it.

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Ospreys Migrating

10-15-18 osprey 014

Banding birds, and the retrieval of these bands, has provided valuable information on the movement of birds. Today we also have the benefit of satellite telemetry, in which a bird carries a tracking device and its location is calculated via satellites that orbit the Earth.  The following is just a sample of what this tracking technology has revealed about the migration of Ospreys.

There are significant differences in male and female timing of migration (females leave up to a month before males), distance traveled and overwintering locations.  There is strong fidelity to overwintering sites as well as to migration flyways.  Breeding pairs of Osprey do not migrate or overwinter together, and adults do not migrate with their offspring.  Ospreys rarely migrate at night over land but inevitably migrate at night when undertaking longer (more than 12 hours) water crossings.

Subtle insights into migratory behavior can be gained by the findings of satellite telemetry, as well.  Their first flight south by juvenile Ospreys is often largely over water. A majority of juveniles migrating over the Atlantic Ocean from Massachusetts to the Bahama Islands flew as many as 1,500 miles over a period of up to 58 hours. The fact that no adults or 2nd year birds took this route over water suggests that juvenile Ospreys learn the coastal migration route during their first trip north.

Overwintering habitat preferences have also been assessed.  Of 79 Ospreys tracked by satellite, 30.4% overwintered on coasts, 50.6% overwintered on rivers, and 19% overwintered on lakes or reservoirs, with differences based on both sex and region of origin.

These few facts don’t begin to exhaust the information gathered from banding and satellite telemetry on Ospreys, much less many other species. They just serve to illustrate how modern tracking technology compliments and increases the information formerly gathered by firsthand observation and banding.

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