When one thinks of vampire bats, friendship and cooperation may not be among the qualities that come to mind for these blood-feasting creatures of the night. But maybe they should.Scientists have provided a deeper understanding of social relationships among vampire bats, showing how those that have forged bonds akin to “friendships” with others will rendezvous with these buddies while foraging for a meal.Researchers attached small devices to 50 vampire bats to track nighttime foraging in Panama, when these flying mammals drink blood from wounds they inflict upon cattle in pastures.