JACKSON, Wyo. (AP) — A trio of sprightly two-day-old cygnets hears their new foster parents calling nearby. Instinctively, the young, captive-raised swans jump off a platform and paddle into the chilly waters of Yellowstone National Park's Grebe Lake.

Bad move.

This is a swan "graft," an effort to trick the two adult swans into raising the three young now swimming toward them.

But "mom" and "dad" aren't enthused. Hovering near their man-made nest platform in the lake, the adoptive parents see the fast-approaching youngsters as pests, rather than beloved offspring. Instead of bonding, they star...