Docent Circle: Field Notes Week of 2004-09-07

Cowbird Chicks Prosper By Sharing The Wealth

Brown-headed cowbirds are born freeloaders. They lay eggs in the nests of other birds, leaving their babes to be raised by adoptive parents. Theory suggests these and other nest parasites should evict any other chicks to hog all the food for themselves. But in fact, young cowbirds live and let live. Now researchers from the University of California, Berkeley and Cambridge University, United Kingdom say that sometimes it pays to share. In the study, the scientists observed cowbirds growing up in phoebe nests. They report in the journal Science that cowbirds raised with two phoebe chicks grew faster than cowbirds raised with one or no adoptive siblings. The researchers theorize that the presence of three gaping mouths spurs parent birds to work harder than the cheeps of fewer chicks. Meanwhile, the larger and stronger cowbird can intercept the majority of the food. UC Berkeley Article

Oak Disease Spreads Via Human Hikers

Human hikers and mountain bikers are spreading a disease threatening California forests. The fungus that causes sudden oak death, Phytophthoraramorum, has killed thousands of oak trees around the state and afflicted other native plants such as rhododendrons and bay laurel with a leaf disease. Previous work had found that the pathogen can be carried by hiking boots. Now J. Hall Cushman of Sonoma State University, California, has confirmed that forest lovers are helping to speed the trees' demise. Cushman took soil samples from forests seemingly clear of the disease and tested them for the fungus. He found the pathogen frequently along trails, but not from samples taken just a few feet off trails. Parks with the most foot, horse, and bike traffic were more likely to have the disease than quieter parks. The findings, which could trigger trail closures in some parks, were reported at a meeting of the Ecological Society of America in Portland, Oregon. The California Oak Mortality Task Force website has more information on the disease.

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