Thursday, May 21, 2009

Warblers, Ovenbirds, Black Throated Warblers

Nature Watch

by Susan Benson,
CNHM Director of Education

"Teacher, Teacher, Teacher!" As a child, many of us may have exclaimed this to
our favorite elementary teachers. Today, it is instead the English translation of
the sound of the ovenbirds. This week we should be hearing this sound in the
forest as this six-inch high warbler returns from its 2,300 mile migration from
Nicaragua. Another sound that should be heard this week is the black-throated
green warbler, singing out to us, "zee-zee-zee-zoo-zee" Although found in two
slightly different habitats, these are both forest-dwelling birds that spend
their summers in northern Wisconsin, and are worth listening for, as we almost
never see them.

Ovenbirds migrate at night, flying 39 miles per hour to reach their northern,
summer home. The term "ovenbird" comes from the shape of their nests, built on
the ground with Pennsylvania sedge that resembles the shape of a Dutch oven.
When we hear the "t-cher" sound, it is the males often singing from near the
ground, and the call gets louder as they sing. Nearby male ovenbirds sing
together. One male begins singing, and the second starts immediately after. They
pause, and then sing one after the other again for up to forty repetitions. The
second joins in so quickly that they may sound as if only one bird is singing.
Ovenbirds hop across the forest floor of Wisconsin's mature forests, preferring
upland deciduous trees, or mixed conifer and deciduous forests. Ovenbirds forage
for insects off leaf litter on the forest floor.

It must be a challenging life being a small, migratory bird. It is believed that
half of all adult ovenbirds die each year. Extensive studies have been made on
ovenbirds in the Chequamegon-Nicolet National Forest on the impacts of forest
fragmentation. In areas where the forests have decreased to very small sizes, egg
predation occurs more frequently. Studies are currently underway in Drummond and
Cable study plots to determine the impacts of exotic earthworms on ovenbirds and
other ground-nesting bird species. Although, not a species of special concern, it
is also believed that the populations are declining in the east as the forest
becomes more mature. With healthy populations in northern Wisconsin, ovenbirds
share a welcome sound to greet other forest dwellers such as ourselves until
early June.

The dark black bib and bright yellow face of the black-throated green warbler is
rarely seen, but the sound is often heard as they sing in coniferous forests. The
males begin their "zee-zee-zee-zoo-zee" in the middle of his territory to attract
females, and later in the breeding season to deter other males. This warbler sings
continuously throughout the breeding season - one individual was heard 466 times
in one hour. These warblers also glean insects from small branches; sometimes
hovering and picking their prey from branches in flight.

The black-throated green warbler is another bird that has challenges in its
summer and winter habitat. They migrate north in the spring from Mexico, where
populations are thought to be declining due to the loss of mature forests. This
species is also susceptible to nest parasitism by the brown-headed cowbird.

When taking a walk outdoors, be sure to be on the look-out for the sights and
sounds of our migratory warblers. Bring your binoculars and bird book, as
warblers are quick to move, and difficult sometimes to identify. Keep a tape or
DVD of bird songs in your vehicle to continue improving your bird song
identification skills. Maybe you'll be lucky enough to spot a "bouquet" or
"confusion" of warblers, which is simply a group of warblers, and is, simply
beautiful to see.

Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility and exhibits, the Curiosity Center and Brain Teasers 2, in Cable at 13470 County Highway M. Also find us on the web at to learn more about exhibits and programs.

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