sentences:  At a common tern colony in Minnesota, a study of spotted sandpipers observed to nest near the tern colony showed that the sandpipers that nested nearest the colony seemed to gain some protection from mammalian predators, but avian predators were apparently attracted to the colony and the sandpipers nesting there were actually more vulnerable.In a study of a least tern colony in Connecticut, nocturnal avian predators in the form of black-crowned night herons and great horned owls were observed to repeatedly invade a colony, flying into the middle of the colony and meeting no resistance.For seabirds, the location of colonies on islands, which are inaccessible to terrestrial predators, is an obvious advantage.