The Bewick`s Wren - Neighborhood Naturalist

Nature you can find in town and the nearby countryside
Corvallis, Oregon
Bewick’s
Wren
Winter 2014-15
Willamette Valley is linked
to important discoveries
about bird behavior and
songs.
In 1969, Donald
Kroodsma was a graduate
student at Oregon State
University. He was in need
of a research subject and
was inspired by a Bewick’s
Wren singing in his Corvallis
backyard. For the next two
years, he studied Bewick’s Wrens
at William L. Finley National
Wildlife Refuge. He recorded
songs, studied their behavior and
tracked their movements. That
research inspired a life-long quest to
decipher the dynamics of bird song.
Today, with the work of Kroodsma and
other field researchers, we know much more
about bird songs and behavior.
he Bewick’s Wren (pronounced like Buick) is a little
brown bird with a lot of spirit and a loud, melodious
voice. It’s common, and there may be one in your
backyard right now, or at least somewhere nearby.
T
In the mid-20th century, it was assumed that
young male songbirds learn their songs only from their
fathers. During his Bewick’s Wren research, Kroodsma
discovered otherwise. After he fledges, a young male will
practice singing, but these utterances are more like awkward
babbling compared to his father’s polished performance.
His song isn’t perfected until after he establishes a new
territory. In the dominance struggle with the local males
around his new home, he assimilates their songs. A similar
learning pattern is common among many songbirds, such as
the Song Sparrow (covered in our Winter 2008 newsletter).
We’re lucky to have Bewick’s Wrens. In some eastern
states, their numbers have declined or they’ve vanished
altogether. I think many people don’t notice them because
they live in the brush and they rarely visit bird feeders. But
scientists have noticed them, and the Bewick’s Wren in the
In most regions, including the Willamette Valley, the
Bewick’s Wren population is nonmigratory. Kroodsma
determined that this leads to song dialects. Since these
birds learn their songs from other local birds, they develop a
unique song culture. A human analogy is the development
article and illustrations
by Don Boucher
photography by Lisa Millbank
Neighborhood Naturalist, Winter 2014-15 v12 #4 • page 1
The nest cup is built within a cavity or on a
concealed ledge. It has a foundation of twigs and
is lined with grass, moss, hair and/or feathers.
of regional accents. In contrast, migration tends to mix up
the population. When these young males learn to sing,
they’re exposed to songs from birds who were raised in
different regions. The result is a more uniform song culture.
In 1997, I was on a mission to learn local bird songs,
and the Bewick’s Wren was one of my biggest challenges.
My bird sound CDs weren’t much help, and now I know
why. Each Bewick’s Wren can have a repertoire of 13 to
20 different songs. If you consider all the regional dialects
throughout its wide range, it means that there are far more
unique songs than any bird sound collection can cover. So,
identifying the Bewick’s Wren song is not like instantly
recognizing a song on the radio—it’s just not that simple.
The eggs are about ⅝” long (shown here at
actual size), and are whitish with scattered dark
speckles. A band
of spots encircles
the larger end.
Fortunately for birders learning to identify the Bewick’s
Wren by sound, there’s an easier alternative to the song.
It commonly makes a sharp, angry-sounding buzz that it
uses to scold any creature that seems to threaten or annoy
it. It’s easy to upset or annoy one. Unlike birds who dwell
in the treetops, a Bewick’s Wren has a vested interest in
what’s going on near the ground. If you pursue a singing
wren in a thicket, it’s likely to scold you once you get too
close. Conversely, a canopy-dwelling bird singing high in
a tree may not even acknowledge your existence.
Some species have simple songs that they don’t learn,
and they sing nearly the same wherever you find them.
The group of songbirds that includes flycatchers, phoebes
and pewees are born with the ability to sing accurately.
When these birds are raised in captivity, away from others
of their kind, they sound just like birds in the wild. There
have been similar experiments on Bewick’s Wrens raised
in captivity. They did sing, so there is an unlearned aspect
to their song. While vaguely similar in sound quality to
wild wrens, the song patterns of these captive wrens were
highly simplified.
Although it’s a challenge, birders can learn Bewick’s
Wrens by sound. There are no shortcuts. Birders who
know their local Bewick’s Wren songs have spent many
hours listening to them in the field. I can offer some
guidance, however. All notes in the song are precise, clear
and loud. There are no weak sounds, no sloppy notes nor
any tremolo. The songs are usually musical and I find
them to be delightful. In the Willamette Valley, its songs
aren’t likely to be confused with our other wren species,
but some songs may resemble those of a Song Sparrow. It’s
common for the wren to make one or more soft, wheezing
notes between each song. Most songs include common,
recognizable phrases. There are nuanced aspects of their
A Bewick’s Wren spends a considerable amount of its time hunting songs, like timbre and tone, that are difficult to describe
in brush, small trees and brambles. Although wrens have a habit of verbally. I know birders, like me, who feel confident
that they can identify a Bewick’s Wren by sound alone.
cocking their tails, this one’s tail is relaxed.
Neighborhood Naturalist, Winter 2014-15 v12 #4 • page 2
Willamette Valley Wrens
Bewick’s Wren
Pacific Wren
The Bewick’s Wren has a bold white eye stripe, pale throat, and a dark cap and back.
The Pacific Wren is our darkest and smallest
wren. It’s the only wren found deep in shady
conifer forests.
House Wren
The House Wren is smaller and plainer than the Bewick’s, with no “eyebrow.” It’s only here
during spring and summer.
Marsh Wren
Brown
Creeper
The Marsh Wren looks most like the Bewick’s, but has a dark patch on the back with white stripes.
Neighborhood Naturalist, Winter 2014-15 v12 #4 • page 3
The Brown Creeper isn’t a
wren, but looks similar. It
habitually hitches up tree
trunks. It keeps its stiff tail
braced against the tree. It has
short legs, a white belly and
lacks barring on the tail.
But there’s a limit to our confidence, since all of us have
encountered an unfamiliar song, only to find out it’s a
Bewick’s Wren. But as mentioned before, I can always rely
on that buzzy scold call.
Watch a video featuring
Bewick’s Wrens songs at
www.neighborhood-naturalist.com
Bewick’s Wrens may sing just about any time of year. Not
long after the winter solstice, singing gradually becomes
more frequent and intense, peaking in spring. Nest building
is started by the male in March, and later, the female helps
finish it. They build in a cavity, like a tree hole or nest
box, and prefer cavities that are near or among brush or
small trees. They’ll readily use human buildings like sheds
or barns where they can find concealed ledges or hidden
cavities. Sometimes they’ll nest in neglected objects like
flower pots, cans, boots or junked cars. The nest is a cup
made of sticks lined with dead leaves, feathers, moss and/
or hair.
An average clutch is about 5-7 eggs. The female incubates
the eggs and both parents raise the babies. After they fledge,
they remain in their parents’ territory for a few weeks.
From mid- to late summer, they set off to find their own
territories, which may be between 100 yards to several miles
away. And it is then that a young male will perfect his song.
Their habitat is nearly any brushy place below 2000 feet,
such as forest clearings, along streams and lakes, backyards,
parks, hedgerows and forests with open canopies. They eat
insects, spiders and similar small prey almost exclusively.
They were historically common east of the Mississippi
but have been reduced to a few, small remnant populations.
One reason for this could be human changes to their
habitat. Another factor is competition with House Wrens.
House Wrens overtake Bewick’s Wren nests and territories
and sometimes destroy Bewick’s Wren nests. The House
Wren’s range has been expanding in the east, which has
coincided with the Bewick’s Wren’s decline. In the west, the
two species coexist without the same impact on the Bewick’s
Wren. In fact, Bewick’s Wrens have been expanding their
range into new areas, even into places already occupied by
House Wrens—so perhaps there are other factors involved
in the decline of eastern Bewick’s Wrens.
At least there are no indications that our western Bewick’s
Wrens are under a significant threat. Which is good,
because if you haven’t yet become familiar with this feisty
and loud wren, there are plenty to find! ó
Neighborhood Naturalist, Winter 2014-15 v12 #4 • page 4
North
American
Deer Mouse
Article and photography by Lisa Millbank, illustrations by Don Boucher
A
s the stars come out on a January night, shrill
squeaks and the rustling of fallen leaves betray
the presence of the North American Deer Mouse.
Though they look something like House Mice, they’re not
closely related. Part of a diverse group of 56 native species
in the genus Peromyscus, North American Deer Mice are
widespread across the continent, living everywhere from
deep forests and subalpine meadows to pastures and
coastal plains. There are almost seventy subspecies of this
highly variable little mouse. Here in western Oregon, our
subspecies (Peromyscus maniculatus rubidus) has darker
coloration, large, sensitive ears and a long, semi-prehensile
tail that helps it clamber through brushy thickets and climb
trees. In eastern Oregon’s arid lands, pale mice with shorter
tails scamper across the sagebrush steppes.
While making its nightly rounds, a North American
Deer Mouse feeds on practically anything edible. In spring
and summer, it shows a preference for insects and spiders,
along with some leaves and fruit. Fall and winter marks a
shift toward fungi (such as truffles and mushrooms) and
seeds. If the deer mouse finds quantities of nuts or seeds, it
caches the surplus inside a hollow log or a vacant burrow.
Deer mice gnaw on shed antlers and bones, possibly for a
mineral supplement or to wear down their ever-growing
incisors. These mice may play an important role in
spreading the spores of fungi and the seeds of many plants,
as do many other native rodents.
We set up an infrared camera near a Dusky-footed
Woodrat’s house one time, hoping to capture videos of the
woodrat emerging from its enormous fortress of sticks at
A North American Deer Mouse is at home in the dark, dusk. Perhaps the woodrat had met its fate in the claws of
with large eyes and sensitive whiskers to help it navigate, a Bobcat or a Great Horned Owl, because it never showed
and a keen sense of smell to detect food, predators and other up. Instead, a tiny North American Deer Mouse emerged
deer mice. While its nocturnal habits generally protect it from the woodrat’s home. It spent each night industriously
from hawks, it’s hunted by a myriad of predators, from collecting hawthorn seeds and returning to cache them
owls to Coyotes, Bobcats, Striped and Spotted Skunks, inside its spacious mouse palace.
weasels and snakes.
Neighborhood Naturalist, Winter 2014-15 v12 #4 • page 5
If it’s not lucky enough to find a vacant woodrat house,
a North American Deer Mouse will take advantage of
any cozy, sheltered place it can find. A hollow tree, a rock
pile, an old bird nest or another animal’s burrow will do,
and these mice occasionally reside in homes, cabins and
outbuildings. The deer mouse builds its nest with bits of
moss, feathers, dried grasses, fur, chewed paper, or other
suitable materials.
During harsh winter weather, the North American Deer
Mouse relies on its food caches, its well-insulated nest and
its ability to go into a daily period of torpor to conserve
energy. It doesn’t enter a long-term state of hibernation
like many rodents do. Instead, during daylight hours, the
mouse will allow its body temperature to drop as low as
55°F. It awakens from torpor before nightfall. Groups of This nest, located under some sheet metal, is just the right size for
up to fifteen deer mice will huddle together in communal a family of five North American Deer Mice. The mice formed bits
nests to stay warm when the weather’s chilly. In early spring, of dried moss into a cup with an inside diameter of about 4 inches.
I lifted a piece of sheet metal and found a group of five
mice curled up together.
Deer Mice and Public Health
In western Oregon, North American Deer Mice are
the primary carriers of the Sin Nombre hantavirus,
which can cause a severe respiratory disease in humans,
with a 38% mortality rate. The mice are unaffected by
the virus. The risk of contracting hantavirus is very low
in western Oregon, with one non-fatal case reported
from Linn County in 2012.
Hantavirus can be transmitted in several ways,
but the primary mode of transmission is through
airborne particles of urine, saliva or feces. The risk of
infection is highest when people clean outbuildings
or attics where deer mice are present. Sweeping
causes virus-laden droplets of deer mouse waste
to become airborne, and these are inhaled into
the lungs. The CDC recommends spraying any
rodent-contaminated surfaces with a bleach solution
before sweeping to reduce the risk of transmission.
North American Deer Mice (and other rodents)
are also reservoir hosts of the tick-borne diseases
babesiosis, ehrlichiosis and Lyme disease.
Protecting the full array of natural predators helps
ensure that deer mouse populations don’t grow to a
level that will increase the risk to public health. And
to put the danger in perspective, the presence of
North American Deer Mice is an extremely small risk
compared with many commonplace hazards in life,
such as driving cars. I don’t worry much about limited
contact with wild deer mice in their natural habitat.
This baby North American Deer Mouse has been weaned recently
and is now on its own. Youngsters have gray fur.
Most of the time, though, deer mice are fairly solitary,
each with its own territory. A male’s territory may overlap
with a female’s, but neither will share its home range with
a mouse of the same sex. The mice communicate with
one another with scent markings and squeaky calls. When
alarmed, they perform a “drum roll” by tapping their
forefeet against dry leaves or sticks, making a distinctive
buzzing sound.
North American Deer Mice can breed almost any time
of year in our mild climate, but they’re least likely to
do so during the colder months. When a female enters
estrus, nearby males will attempt courtship. Researchers
studying these mice have learned that the male “sings” a
a series of ultrasonic calls that seem to facilitate mating.
A normal litter is three to five baby mice, born after a
gestation of three to four weeks. In some litters, the young
have different fathers. The babies weigh about two grams
Neighborhood Naturalist, Winter 2014-15 v12 #4 • page 6
Deer Mouse Predators
Coyote
Bobcat
Northern Saw-whet Owl
Gopher Snake
at birth, and like all baby mice, they’re naked and pink,
with sealed ears and eyes. If the mother feels that the nest
site is not secure, she’ll move her young. Very young babies
will cling to her nipples as she walks. She carries larger
babies in her mouth, one at a time. By the time they’re
one month old, they’ll have grown full coats of gray fur,
and their mother evicts them from her territory soon after
weaning. Within a couple of months, they’ll be having
babies of their own.
⁄ – ½"
wide
5 16
¼ – 7⁄16" long
These beautiful, abundant little mice usually go
unnoticed, like other small, nocturnal creatures. It may
take a real effort to find them. I look for sleeping mice
under old tarps, boards, sheet metal or slabs of bark. Look
for their tiny tracks in fine silt. Or take a moonlit walk in A front foot track in wet silt. It has a distinct palm with three pads
the winter woods, and listen as they rummage around in and two heel pads behind it. Like most rodents, a front track registers
four toes while a rear track (not shown) registers five.
dry leaves. ó
Neighborhood Naturalist, Winter 2014-15 v12 #4 • page 7
Similar Mice
Pacific Jumping Mouse (Zapus trinotatus)
This mouse has an extremely long tail and legs
modified for jumping, and lives in streamside thickets.
It hibernates, and doesn’t enter houses. It has a
strongly contrasting dark stripe down its back.
North American Deer Mouse
(Peromyscus maniculatus)
The North American Deer Mouse is the only mouse
in our area with a white belly and a bicolored tail. The
coat color is somewhat variable.
Meadow voles (Microtus sp.)
Several species of voles are common
throughout our area. They’re
plump, short-tailed,
hamster-shaped rodents
with small, furry ears.
This is probably
a Gray-tailed
Vole (Microtus
canicaudus).
House Mouse (Mus musculus)
The House Mouse is a Eurasian rodent and the most common
mouse found inside buildings. Its coat is usually evenly gray,
with no contrasting markings.
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Neighborhood Naturalist, Winter 2014-15 v12 #4 • page 8
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EVENTS
Naturalist Adventures
Third Sunday of the Month, 9am. See maps on website
February 15, Jackson-Frazier Wetland, Corvallis.
Meet at parking lot at north end of NE Lancaster St.
March 15 Luckiamute State Natural Area. Meet at North unit. From Spring Hill Drive go north on
Buena Vista Rd. for 1.2 miles. Watch for sign for “Luckiamute North” access road.
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www.neighborhood-naturalist.com/neighborhood-naturalist_events.htm for exact location.
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June 21 Woodpecker Loop and/or Mill Hill, Finley National Wildlife Refuge. Meet at Woodpecker Loop
parking area from Finley Refuge Rd.
Rain or cold will not prevent us from going out and enjoying nature. Remember to dress for rainy
and/or cold weather. May be canceled without notice if road conditions are dangerous.
For other events or more information: www.neighborhood-naturalist.com
Don Boucher, 541-753-7689, bouchdon@peak.org
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