With an estimated 400 mallards living in the arboretum, campus officials are studying reasons for their growing numbers, potential risks to the environment, other wildlife and human health, and best ways to manage the duck population. Campus officials say the population-apparently thriving on bread crumbs and other food left by people-may be far more than the arboretum can naturally support. And both the bread and the resulting duck overcrowding, they say, may be damaging water quality, increasing duck mortality and fostering diseases that can spread among the resident mallards, migratory waterfowl and other wildlife. Officials say people who leave food for the ducks may unintentionally be feeding rats as well. Robert Powell, a chemical engineering and materials science professor, said he's spotted rats near the Wyatt Pavillion Cafe while jogging with colleagues through the arboretum. "I've seen them numerous times," he said. Powell headed an ad hoc committee last year that developed a plan for improving the Arboretum Waterway. As part of that plan, the committee strongly urged the campus to work with appropriate state and federal agencies to develop a program to manage the duck population. "Certainly the ducks aren't the only issue" in improving water quality, Powell said. "It's just one of the many things that we recommended." Other committee recommendations included using reclaimed water, building a series of cascades and regularly skimming debris from the waterway to create flow and improve water quality in the elongated pond. Campus recommendations to manage the duck population go back nearly a decade. Too many ducks may not be so good for the web-footed birds themselves. Campus officials suspect that overcrowding may be causing increased aggression among the ducks-with growing numbers of injured and dead birds the result. Ducks also cause an estimated $16,000 a year in damages to landscaping and lawns, as well as the costs of cleaning their wastes off arboretum paths. Representatives of Environmental Health and Safety, the arboretum and the Grounds Division have formed a task force that is seeking to find an "ecologically sound and humane" duck-management plan. No plans exit to trap or kill the ducks. Steps under consideration include posting signs to inform visitors of a campus policy forbidding feeding of waterfowl in the arboretum; inspecting duck nests and removing eggs to reduce the number of ducklings born each spring; and regular surveillance of arboretum wildlife, and quick removal of dead or sick animals to prevent disease outbreak. Such actions are supported by both the state Department of Fish and Game and the Animal Protection Institute, a wildlife advocacy organization that is advising the campus. "We are concerned with the humaneness of the process and that the treatment be responsible and ongoing," said Monica Engebretson, wildlife issues program assistant to the Animal Protection Institute in Sacramento. "The whole situation is an artificial one, and steps...to reduce reproduction and discourage feeding are the things we encourage." But after a meeting with wildlife advocates and community duck enthusiasts earlier this month, campus officials agreed to do further study on the extent of the problem. Feeding bread to ducks has been blamed for duck deaths elsewhere in California. Avian botulism has caused the deaths of more than 20 male mallards since late October at Niguel Regional Park in Southern California. Carol Cardona, a UC Davis assistant veterinary professor and an authority on poultry viruses, said she believes that bread is the culprit. "People are feeding it to thousands of ducks, and it's the worst thing in the world for them," Mendoza told the Los Angeles Times last month.