To understand how they got them. Your birds were in a pen and not locked up in a coop?[/quote :
The fence... I am not sure what it is called, but it is about 1" x 2" rectangles and 4 or 5 feet tall. The "egg flock" were in their coop, but the door was left wide open (because we have never had this problem before!). The Silkies were in a pen like this
http://www.freewebs.com/gracefulbantams/chooseyourbird.htm but their nest box did not lock, so I think that was the "weak link".
The animal (or animalS) must have crawled over the fence, because there was no sign of digging anywhere!
I'm so sorry. We had an issue many years ago, with a fisher cat (or just our assumption of one) getting one of our 10 cochins every night. They would roost in the barn and weren't penned. Finally, we thought of the bright idea (imagine that???) of turning on the electric fence...and poof!...problem solved. We had one cochin left at that point. They were the cutest little birds, and followed us everywhere.
Today, we have a flock of 23 pullets and one rooster - the roo is a NH Red, and the rest are a combination: Black Star, NH Red, Buff Orp, Barred Plymouth Rock. They are spoiled rotten, and their pens and houses are as secure as Fort Knox...until the next breach. Then they'll be as secure as Guantanamo Bay.