Oooooh - those Fishers. Many a fine cat has been lost in my area to those beasties. My husband's friend watched helplessly out the window as one grabbed his cat and was gone in a flash. When I was a kid you never heard of Fishers coming into people's yards; they were reclusive and rarely seen. Over the last 20 years or so, they are either getting more prevalant, or bolder, or I don't know what.
As WestChesterfield says, they are not particularly phased by human presence, either. I came across one eating some nasty snack on a mountain road one night, and I drove right up to him, beeping the horn, and it was a good 30 seconds of him glaring at me before he reluctantly grabbed his kill and ambled off.