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' accidentally kills the siren, leading the others to pretend to be acorns and chase him.
At the end of the film, the sirens, detecting more prey, found Gutt, a piratical gigantoptechus, in a cave. And one of them appeared before him as a mermaind of his kind, lying in a bounty of fruit inside a massive shell. She soon managed to seduce Gutt, but revealed her true form when it got too close to her, grabbing the ape by the lips, pulling him as the shell closed. All that could of Gutt are screams of pain as more sirens swam towards for the shell. The sirens eaten Gutt alive, making their specie extinct.
- Whether the Sirens are truly evil or not is up for debate, as while they tried to devour The Herd and possibly succeeded in devouring Captain Gutt, they could be just fierce predators that are trying to survive in a changing world. Furthermore, when Scrat trampled the Siren who posed as his acorn to its death, the other Sirens immediately proceed to hit him as acorns in the same way he killed the Siren, proving that they indeed care for each other of their kind.
- The Sirens are the main reason Gutt wasn't Pure Evil as they cast an image that Gutt fell in love with. Since Pure Evils cannot feel love, Gutt is not Pure Evil.
- Unlike real mermainds who have the real yet seductive appearance and only use the corner to attract, they use the corner for both cases.