Possible Re-Write

This plot change deserves some consideration.
Including the falcon is not that bizarre an idea. Woman of our heroines stature often took up falconry; it would add a sensitivity to her character that further clashes with the Duke, (Maybe he scowls at it at some point).
The falcon is an indication that she is no bashful introvert.
It gives the whole animation a little more spice, its an unusual, and not at all cliched element.
It gives us further reason for the sweeping camera movement at the start.
My only concern is that we'd have to be careful with how its introduced, it has to be associated with the Duchess at the start but we don't want to draw too much attention it. the diamond and the relationship between Duke and duchess is the important thing at this point.
All that aside, hears an extended synopsis for this version. The name for the animation, as well as the train, might be too obvious, but theres a nice conneciton with raptor; it means bird of prey but its from the latin raptus which means 'to seize' both property and people, ah ha!

The Flying Raptor.

The Duke and Duchess are traveling to the Duke's country on board the world famous Flying Raptor.
the Duke admires his reflection in the Duchesses Diamond necklace, she is disgusted by his vanity and turns her attention to her falcon, perched nobly on her gloved hand.
The camera pulls out of the window as the Duchess stands and releases the bird out of the skylight.
The camera pulls further out as the Duchess as she watches the bird enjoy the freedom she craves; the camera pulls out and around the train, following the falcon.
The train is racing through a mountainous reaching, above the cloud line, the sky is a deep pink as the sun sets.

Revealed, clinging to the last carriage is a bandit. He watches the falcon soaring past, then climbs onto the roof of the rocking carriage; the camera moves around him, he reaches the roof, staring determinedly down the train.

Back in the first carriage, the duchess is looking out the window, presumably watching her falcon, she glances at her watch whilst the Duke pats his hair, looking at his reflection in the back of a silver plate.
There is a crash from above, both the Duke and Duchess look startled as the Bandit drops into the carriage, he snatches the diamond before running off down the train, the Duke is enraged and chases after him.

The Bandit knocks on a compartment door and keeps running, the door is flung open by a confused looking passenger just as the Duke draws level with it.
The door closes and the stunned Duke sees the Bandit at the end of the train standing next to an open door, holding the diamond up. The Bandit grins, and nonchalantly tosses the diamond out of the doorway. The Duke rushes to his feet and runs to the open doorway.
The camera begins in close-up and pulls away from the count. The camera passes out of the doorway to show the count reaching the doorway and the Bandit running in the opposite direction down the train. The count looks frantically for the diamond from the open doorway.

Back at the first carriage, the countess is unhooking the coupling to separate the cars, the gap widens, just as the Bandit leaps the gap above her head.
The Bandit lands in the fist carriage next to the Duchess and they embrace. As the train pulls away from the camera the Duchess holds out her gloved hand and her falcon alights, clutching the diamond necklace in its beak.