David Owen: Why Do Pandas Have Such Difficulty Breeding in Zoos?: The New Yorker A female giant panda unambiguously signals her approaching receptivity to mating. She wanders over a wide territory and scent-marks stones, the ground, and other surfaces with a waxy, hormone-rich secretion from a gland under her tail. She walks through water, to spread her scent farther. Her main vocalization changes from a throaty whinny to a high-pitched chirp, which one zookeeper translated for me as "I'm here! I'm here! My time is coming! She masturbates, and when she encounters an adult male at the critical moment she lumbers toward him, rear end first, and lifts her tail. Still, things don't always work out. David Wildt, the head of the Center for Species Survival at the National Zoo, in Washington, D.C., told me, "Some pandas know how to have sex, and some don't." The pair at the National Zoo - Tian Tian (male) and Mei Xiang (female) - don't. They have been together at the zoo since 2000, but until last week they had produced just two cubs, both by artificial insemination, and one of these had died. At the end of last week, Mei Xiang gave birth for a third time, live on one of the zoo's panda Webcams. The latest arrival is also the product of artificial insemination. As Wildt described it to me, Tian Tian and Mei Xiang are simply "reproductively incompetent." A key difficulty is that Mei Xiang places herself in what he called "pancake position" - flat on her stomach, legs outstretched - and Tian Tian isn't assertive enough to lift her off the ground. Rather than mounting from behind or pulling her toward his lap, he steps onto her back and stands there like a man who has just opened a large box from Ikea and has no idea what to do next. . . .