[ No headline ]

Volunteers began round-the-clock duty at the National Zoo in Washington, D.C. , watching the female panda Ling-Ling and hoping she is ready to give birth to the nation's first panda cub. After eight years of trying, Ling-Ling and her male partner, Hsing-Hsing, mated successfully this spring, boosting hopes the 250-pound gift from the Chinese government will become a mother.