-By Daniel Eagan

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Kids won't get all the references in Rio, the latest animated feature from Blue Sky Productions, but they will soak up plenty of color and music in this catchy 3D cartoon. Adults will appreciate the strong thread of nature conservancy that runs through the film, along with Rio's infrequent but sincere stabs at social awareness. But it's the action, slapstick, and irresistible images of Rio itself that will delight children.

The opening credits offer a dazzlingly choreographed introduction to rainforest bird life, eventually focusing on Blu (voiced by Jesse Eisenberg), a rare macaw who has not yet learned to fly. Kidnapped by smugglers and shipped to Minnesota, he is rescued and raised by Linda (Leslie Mann), proprietor of a small-town bookshop. Brazilian ornithologist Tulio (Rodrigo Santoro) persuades the reluctant Linda to bring Blu, the last male of his species, to Rio to mate with Jewel (an enthusiastic Anne Hathaway).

It doesn't take long for Tulio's plans to go awry. Smugglers spirit the macaws off to a hiding place ruled by the evil cockatoo Nigel (Jemaine Clement). Although they are chained together by the feet, the macaws manage a daring escape. But since he still hasn't learned to fly, the frightened Blu is little help when Jewel tries to return to the rainforest. Forging a guarded relationship, the birds must rely on new friends to get their chain removed, chased all the while by Nigel and his cohorts.

Meanwhile, Linda and Tulio search Rio for Blu, aided by Fernando (Jake T. Austin), a homeless orphan who has worked with the smugglers. Since it is the eve of Rio's famous Carnival, the city is teeming with festive crowds. The birds and the humans wind up performing in a massive parade before a sudden reversal forces Blu to confront his worst fears.

Just as many scenes in the story take place in favelas as on beaches, giving Rio at least a modicum of social awareness. The film's darker moments, including a ghastly tableau of imprisoned birds and a 3D-enhanced encounter with a table saw, give a welcome edge to Rio's generally sugary tone. And although Blu can't fly, the screenwriters have worked in several ingenious airborne scenes that make excellent use of the city's stunning scenery.
Considering the setting, it's surprising that Rio has only two full-fledged songs, although the soundtrack is filled with snippets of everybody from Sergio Mendes to will.i.am. Nigel does get to boast about his villainy ("Like an abandoned school/I have no principles") in a funny number, but another song or two could have brightened the film's mood, which tends to sag in the middle.

Hathaway, who even sings a bit, is a delight throughout. George Lopez is comforting as a helpful toucan, while Tracy Morgan, who turns up briefly as a sort of locksmith, adds his reliably unpredictable humor. The impressive animation uses 3D adroitly, saving the big effects for special occasions like a fly-around of the Christ the Redeemer statue.

Fox is releasing Rio with Scrat's Continental Crack-Up, a clever short featuring the popular star from the Ice Age franchise.