I am heartbroken for your poor birds, for the terror and the pain they endured. And I am so sorry for your pain and anguish too. If you can, give some Rescue Remedy to the survivors (health food stores have RR) - it has a nontoxic calming effect. You can put a few drops in their water for several days.
It's a confounding problem we humans have scripted. New Jersey has ~ a couple thousand black bear but has swelled to house over 8 MILLION humans at this point. We have deleted so much natural habitat throughout the state that the bear are venturing more and more into areas occupied by humans to find food. Not to say bear wouldn't sometimes visit human's places anyway (they would) but it is our population, not theirs, that has literally exploded in the past few decades. And along with us comes our absolute litany of stuff - houses, roads, malls, schools, etc. - all former wildlife habitat. And so the number of conflicts has risen. What to do? Is it going to get to the point that we get rid of everything other than ourselves that could present a threat or do we share some space, preparing well so as to avoid conflict? The responses to this question will vary greatly depending upon who is asked and as such, it remains an unsettled question but while it remains unsettled, we continue to build, build, build, as though there are no repurcussions.
I hate that beautiful innocent beings are mauled in this world - by bear, by dogs, by anything at all - so for me, the only answer is to bear proof in bear country or to not have birds in such areas if bear proofing is a losing proposition. Often the bear hunted and killed in the forest are not the ones that are choosing to visit human yards so a hunting season is not a guaranteed solution. Just as laws governing dogs sadly do not keep chickens safe. The only way to keep them safe from dogs is to fortress the chicken "territory."
I am terribly sorry and tremendously sad about your birds and wish I had the power to rewind the clock to before that fateful moment so that the outcome could be rewritten. I would do it in a flash.
I couldn't read every post in this thread carefully but I'm sure you are not keeping any remaining birds in the same area at this time. I hope you suffer no further heartache.
JJ