If that spooky, hundred-year-old dusty look doesn't come naturally, fake it with hot-glue cobwebs; we "spun" them over realistic-looking stuffed birds.
Source: Halloween 2004, Volume 2004 Special Issue 2004
Hot-glue pads, from dickblick.com
Low-melt trigger glue gun (23601-0000), from dickblick.com
Place several hot-glue pads around the area you want to cover in webs, about 3 inches away from your display. Fill a low-melt trigger glue gun with hot glue; set the gun on low.
Squeeze out a dime-size pool of glue on one of the glue pads, then place the tip of the gun into this glue and quickly pull the gun over the object and rest the tip on another pad. Squeeze out a second blob of glue on this pad, and loop over your object again.
Repeat until everything looks as if it hasn't been cleaned in decades. Once the webs harden, carefully loosen them from the pads.