BLACKSBURG, Va. -- Populations of many grassland bird species have declined significantly in the last 30 years, according to breeding bird surveys. One cause may be farmers' increased use of exotic cool-season grasses, report Virginia Tech fisheries and wildlife sciences faculty member Carola Haas and research associate Russell Titus.
At the 83rd annual Ecological Society of America meeting at the Baltimore Convention Center Aug, 2-6, Titus will present a paper on the density and nesting success of avian species in native warm-season and exotic cool-season grasslands. The Monday, Aug. 3, 11 a.m. presentation is part of the Animal Population Ecology 1 symposium, 8 a.m. to noon in room 307.
"Because they occupy short-lived patches of earth, birds such as the Eastern meadowlark, field sparrow, and grasshopper sparrow should be efficient colonizers," Titus explains, "but many sites that appear suitable in the eastern United States remain unoccupied. We think that may be due to the farmers planting more exotic grass species in lieu of native grasses."
Haas explains that farmers have been increasing their use of nonnative cool-season grasses to improve the nutritional quality of livestock pasture. After its first year, the study appears to indicate that birds don't nest in some of the new grasses because some varieties don't bunch and leave dirt spaces that allow the birds to move around on the ground. Also, Haas says, cool season grasses can be mowed earlier than warm season grasses, "before the first nests have fledged."
The researchers are also looking at whether insect populations differ among grass varieties. "A community of native plants support native insects. The exotic grasses may not support the insects that the birds like to eat," Haas says.
She would also like to determine the economics of establishing exotic grasses. "If they require more inputs than native grasses, they may not be as advantageous as farmers hoped."
For more information, contact Dr. Titus at 540-961-0003 (H), 231-3329 (O) or rtitus@vt.edu, or Dr. Haas at 540-231-9269 or cahaas@vt.edu. (She will be unavailable until July 30. She will be at the conference.) Learn more about Dr. Haas' work at http://www.fw.vt.edu/fisheries/HAAS.