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KERN RIVER RESEARCH CENTER
The following is an article written by star volunteer / researcher
Terri Gallion. It is reprinted with permission. All rights remain
with the Kern River Research Center, no permission is granted or
implied for duplication in any form. Please contact the
research center
about this article.
Fieldnotes: Winter 1994 Vol 3 No. 1
SUMMER TANAGERS ON THE KERN
by Terri Gallion, Research Assistant
"The sight of a male Coopers Tanager...is a vision of
ravishing redness and one's first impulse is to admonish the
vision for its rashness. One day in Arizona the writer spent an
hour watching a waterhole .... Among the doughty visitors came
this .symphony in red, a superb old male Cooper Tanager. As he
drank, or rather, sipped,.., he was utterly unconscious either
of my frank admiration or of lurking dangers. Believe me, what
with image and reflection, that portion of the pool wherein
Piranga drank was illuminated for a season."
William Dawson (1923) "The Birds of California".
Despite the fact that the Summer Tanager is a spectacularly colored
bird, and is locally common in the eastern United States, it's
natural history is poorly known. The male Summer Tanager is an
unforgettable brilliant neon red while the female is yellow. The
Summer Tanager is one of only four tanager species, along with
Western, Hepatic and Scarlet Tanagers, that regularly breed in the
United States and winter in the tropics. The remaining 238 tanager
species breed in Central and South America. The population of Summer
Tanagers on the Kern River is the most northern and western breeding
population in California.
There are two subspecies of Summer Tanager, the Eastern Summer
Tanager (Piranga rubra rubra) and the Cooper's Summer Tanager
(Piranga rubra cooperi). Cooper's Summer Tanager is a
brighter and larger bird, with a proportionately larger bill than
its eastern counterpart. The eastern subspecies breeds in habitats
ranging from pine to oak woodlands and at a wide range of
elevations. In the West, Summer Tanagers are restricted to riparian
woodlands and to lower elevations. Destruction and fragmentation of
this habitat has imperiled many of our migratory birds including the
Summer Tanager.
Cooper's Summer Tanager breeds as far east as western Texas, north
to southern Nevada and south into Mexico. Historically, the Cooper's
Summer Tanager in California was known only from the Colorado River
and as a rare vagrant on the coast of California (Grinnell and
Miller, 1944, "Distribution of Birds of California"). The population
of tanagers on the South Fork Kern River was not detected by Joseph
Grinnell of the Museum of Vertebrate Zoology during his survey here
in 1911. Today this is the largest population of Summer Tanagers in
California. This range expansion to the northwest may be related to
extensive destruction of habitat along the Colorado River over the
past 60 years.
When I looked in Ehrlich's "Birders Handbook" for basic life history
information, I learned I was dealing with a mystery bird. They have
been studied so little that even the most basic life history
information has never been recorded. Included among the things not
known are their mating behavior, nest shape and structure, foraging
methods, which sex incubates, and fledging age.
In 1990, I spent two weeks observing the nesting behavior of Summer
Tanagers on the Kern River Preserve. I knew that even the most basic
observations that I made would be significant. Breeding pairs were
easy to find because they were quite vocal. The male sang often and
both the male and female frequently gave PIT-TI-TUCK contact calls.
I listened for a singing male, followed him until I saw a female,
then watched until one or both approached a nest. If the pair had an
active nest, only a short time was required before they revealed its
location. I became fascinated with their behavior and, with help,
was able to find five nests in almost as many days. I observed one
of the nests from hatching until a few days before fledging.
The male moved in a circuit within his territory consisting of a
dozen or more singing perches. He perched on each in turn and sang
for several minutes. The male and female interacted frequently with
calls and diving and chasing behavior when off the nest. While the
female was incubating there were numerous food exchanges with the
female begging like a fledgling. These behaviors revealed something
of the tanager's personality and showed an intimacy within the pair
that I had not seen in other species.
From my initial findings it seems that the tanagers on the South
Fork are using mature trees, mostly Fremont cottonwoods, for both
nesting and foraging. They nested high in the trees (10 -17 m), used
the mid-canopy for foraging and singing, and frequently foraged near
the ground (1-4 m). Perhaps most interesting was the apparent
specific aggression they presented to Brown-headed Cowbirds. On 26
occasions, I saw pairs of tanagers attack and aggressively drive off
cowbirds. Almost all these attacks were directed toward female
cowbirds. Could this aggression have developed as a method to avoid
parasitism?
Terri continues to study Summer Tanagers in the vicinity of the Kern
River.
NOTE: the
KRRC was disbanded and reformed as the
Southern Sierra
Research Station
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