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Volume XXIV, No. II
March, 1975
PUBLISHED BY THE ORNITHOLOGY GROUP, OUTDOOR NATURE CLUB, HOUSTON TEXAS
ROOSTING RICE-BIRDS by Dr. Dan M. Johnson
In February I960, Vic Emanuel reported the arrival of 20,000 brown-headed cowbirds on
the Rice University campus (Spoon b 111 8CM):4). Both Vic and the cowbirds departed
that spring. For the next five years alumni recall pigeons, great-tailed grackles,
and barn owls, but no roosting cowbirds. Jim Ellis' report of 200,000 birds near North
Blvd. In March 1963 (Spoonbill ll(ll):6) Indicates that they were never far away. The
barn owls were eliminated as a 'nuisance' in May 1965, shortly after Margaret Anderson
had watched them feeding young. Some say the cowbirds' return In 1966 was Athena's
revenge for that unconcionable crime against her creatures; if so, her vengeance has
been fierce!
For the last ten winters, a 'blackbird' roost has formed In live oak trees on campus,
and a nightly rain of vengeance-drops has pelted sidewalks, gardens, parking lots,
scholars and lovers. The magnitude of the problem has Increased over the years. In
January 1970, when the U.S. Fish and Wildlife Service conducted It's nationwide survey
of roosts, there were 15,000 cowbirds ifl trees around the Chemistry lab; since 1971,
the roost has occupied most of the campus, including the area around the President's
home, and the birds have numbered in the hundreds of thousands or more (our estimate
for early February 1975 was 1.24 million). Where have they come from? In 1970 the
major roost In Harris County (1.6 million birds) was In a wooded area near the corner
of W. 18th and Seamist, a favorite birding spot known well to Avis Brister and the
brothers Cureton. Clearing of that woods began in 1970-71, coincident with a dramatic Increase In the roosting Rlce-blrd nuisance. The old traditional site, though
much diminished, Is still occupied by the early-roosting birds from September to December; then the whole roost moves to Rice together. This year the big move came between Christmas and New Year's, just In time to greet s+udents returning from the
hoiidays.
Though I arrived at Rice wlwilrds In 1970-71, I was not Immediately fascinated by
them. I am not an ornithologist, but a population ecologlst Interested In the Influence of predacious Insects (especially damselfly larvae) on prey populations. It was
only two years ago that I realized what a unique educational and research opportunity
was being provided by the cowbirds' annual visit. Since then the students In Population Ecology Lab, who seem much more fascinated by birds than bugs, have been monitoring death rates, estimating population size, and observing social behavior within the
roost. We hope to understand what influences mortality of over-wintering bird populations. What are the causes of death—weather?, starvation? diseases? or pesticides?
Are death rates density-dependent? Does a social hierarchy Influence which birds die?
Whatever the reason, male cowbirds seem to be particularly susceptible, especially In
February and March.
This year birds from particular locations within the campus have been banded and marked with colored plastic leg streamers: dark blue, light blue, and white. We are hoping to learn whether those roosting in different areas also feed in different areas
during the day. Thanks to the Houston Post, the Spoonbill, and the Interest of many
0G members, we've been getting a remarkably high number of sightings of color-marked
birds. (Laura Greenbaum was not only the first to spot one of our streamers, but Is
also the undisputed champion with more than 50 sightings reported!) Bruce McDonnel
and Philip Samuels, who are doing the banding as a senior research project, will have
more to report on their findings In a later Spoonbl11■ But one aspect of the data is
Intriguing, because It may provide a clue to the reason why male cowbirds have particularly high death rates. Though the ratio of males to females banded Is 4 to I, the
ratio sighted at feeders has been 8 to I. Does this Indicate that males have a different feeding strategy? Could that difference explain why males out number females
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