"The speed, magnitude and extent of the recovery were surprising and suggest that even severely degraded systems can recover quickly, at least in some cases, after cattle removal," say David Krueper, who did this work while at the U.S. Bureau of Land Management in Sierra Vista, Arizona, and is now at the U.S. Fish and Wildlife Service in Albuquerque, New Mexico; Jonathan Bart of the U.S. Geological Service in Boise, Idaho; and Terrell Rich of the U.S. Fish and Wildlife Service in Boise, Idaho, in the April issue of Conservation Biology.
Many animals in the arid southwest depend on riparian habitat for its water and lush plants. In Arizona and New Mexico, most vertebrates use riparian areas during at least part of their lives; and throughout the western U.S., the diversity of breeding birds is higher in riparian areas than in all the other types of habitat combined.
To help determine how well grazed riparian areas can recover after cows are removed, Krueper and his colleagues monitored the diversity and abundance of 61 bird species in the San Pedro Riparian National Conservation Area in southeastern Arizona, which is 43 miles long and roughly 2-5 miles wide. Every year, 5-10 million songbirds migrate along the San Pedro River. The researchers monitored birds during the breeding seasons of five years (two before and three after the cattle were removed) in three types of plant communities (riparian, mesquite grassland and Chihuahuan desert-scrub). They also determined the density of vegetation at the peak of summer growth several times over the course of the study.
Krueper and his colleagues found that removing the cows dramatically increased the vegetation in the study area: the density of native plants (such as grasses, cottonwoods and willows) increased 4-6 times in the riparian and mesquite grassland communities.
The researchers also found that the abundance of birds increased. Of the 61 species studied, 26 increased and 8 decreased in the study area. The birds that increased included several "species of special concern", such as the yellow warbler and summer tanager.
Only one of the species that increased (the common raven) also increased elsewhere in the region during the study period, suggesting that the increases were due to getting rid of the cows. Three of the species that declined in the study area (the house sparrow, eastern meadowlark and black-throated sparrow) also declined elsewhere in the region during the study period, suggesting that the decreases were not related to getting rid of the cows.
"Our results suggest that removing cattle from riparian areas in the southwestern United States can have profound benefits for breeding birds," say Krueper and his colleagues.
CONTACT:
David Krueper (505-248-6877, dave_krueper@fws.gov),
Jonathan Bart (208-426-5216, jbart@eagle.boisestate.edu),
Terrell Rich (208-378-5347, terry_rich@fws.gov)
For PDFs of papers, contact Robin Meadows robin@nasw.org.
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http://www.conbio.org/SCB/Services/Tips/2003-4-April.cfm
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Journal
Conservation Biology