FBH member Dave Kabatchnick photoed these three young fishers, probably litter-mates, near Hemenway Hill in the Blue Hills on July 4th.      Fishers are tree-dwelling members of the weasel family that can weigh up to twelve pounds. They are fierce predators and can kill squirrels, rabbits, and porcupines. Although they spend much of their time on the ground, they are found only in forested areas.       Nearly driven out of New England by hunting and trapping, fishers have recolonized much of Massachusetts, and were first reported on the Cape this year. They have been in the Blue Hills since at least 2003, when FBH member Robert Mussey found tracks near Unquity Road. So far as we know, this is the first time they have been photoed in the Reservation.