AN UNKINDNESS?

I just discovered to my horror that the collective noun for a group of ravens is an UNKINDNESS.  The collective noun for a group of crows is a murder.  Who came up with these UNKIND terms??  It must be a European thing from the time of the black death- with so many corpses around the crows and ravens had much to eat much to the horror of the people.  Nature's recyclers.  
We had a large group of juvenile ravens fly in last night and pick the big redwood tree next to the new deck for their nightly roost.  It is so marvelous to watch- birds flying in from all directions- choosing one tree and then another- flying to and fro until they settle on one particular tree.  Once they decide on a tree, they all settle in and quiet down.  At that point ,between the darkness of the interior of the tree and the night falling it is impossible to see the birds.  I however know they are there and am very pleased indeed.  This morning I went to the window to see them fly out into the world, but missed them- got up a little too late.  I hope they will return one day.  One never knows how they chose their nightly tree refuge.