Duck numbers are down, but only slightly, according to the U.S. Fish and Wildlife and Canadian Wildlife services' Waterfowl Breeding Population and Habitat Survey. An estimated 31,735,000 birds will be heading south this fall, compared to 32,164,000 last season, a decline of about 1 percent. That should mean similar hunting opportunities for Southern duck hunters in the Atlantic, Mississippi and Central flyways. Of course, as waterfowlers learned two years ago, population estimates hardly matter if cold weather doesn't jump-start the birds on their migration.