Nat is the son of the captain of the ship, The Dolphin, which, in addition to transporting passengers, delivers items that people have ordered. In chapter 14, he tells Kit of a very peculiar order, a fascinating shipment that actually pertained to Kit.
"Sixteen diamond-paned windows ordered from England by one William Ashby. They say he’s building a house for his bride. A hoity-toity young lady from Barbados…"
The “hoity-toity” young girl from Barbados is actually Kit Tyler, and Nat is mocking her because he is a hurt and jealous in discovering the news that his love interest may be interested in someone else. Previously, there was some sort of connection between Kit and Nat, and he is upset that, not only is she seemingly engaged, she failed to confide in him. He goes on to insult her by using the metaphor of a little bird, Kit, that gobbles up a fat partridge, the wealthy William Ashby.