The Sirens are minor antagonists of Ice Age: Continental Drift. They are fish-like carnivorous animals with needle-sharp teeth that resided near an island. They are based on the sirens of Greek mythology, which were legendary sea nymphs depicted to lure sailors to their deaths through their enchanting voices (in this case, their voices when impersonating someone sound like the being they're impersonating, albeit sounding autotuned). In the film, they trick the heroes and the film's main antagonist.
Sirens are sea creatures that are hungry for flesh. They usually lie on long rock outcroppings near the ocean, where they would try to lure in any creatures that got close by casting images of whatever they found most attractive, be it loved ones, an attractive potential mate or even, in the case of Scrat, the Saber-toothed squirrel, items, such as Scrat's prized acorn. Scrat, trying to bury the 'acorn' accidently kills the siren, leading the others to pretend to be acorns and chase him.
At the end of the film, one of the sirens appears before Gutt, as a female of his species in a huge shell. When Gutt gets too close to the shell, the siren reveals its true form, seizes Gutt by the face and pulls him into the shell, which clamps shut, all that could be heard was Gutt's shouts of pain and the chomping sounds of the siren. It is presumed that the siren devoured Gutt alive, thus making his species extinct.