In "A Visit from Saint Nicholas," line 19 compares "coursers" to "eagles." Is there a "trick" meaning to this question?
But a miniature sleigh, and eight tiny reindeer,
With a little old driver, so lively and quick,
I knew in a moment it must be St. Nick.
More rapid than eagles his coursers they came,
And he whistled, and shouted, and called them by name;
"Now, Dasher! now, Dancer! now, Prancer and Vixen!
On, Comet! on Cupid! on, Donder and Blitzen!
Actually, no, this is not a trick question. By calling the reindeer "coursers," the poet is comparing them to horses, not to eagles. The line reads: "More rapid than eagles his coursers they came." He's not saying that the reindeer are like eagles; he's saying they're like coursers, horses.
In the Middle Ages, coursers were used as warhorses. They were smaller and less expensive than the destrier, another breed of warhorse. According to horseguild.com, the courser was a "steady, long winded horse" that we'd refer to as an "endurance horse" today. That sounds like the perfect description of Santa's reindeer to me. They certainly had to be strong and long winded, able to endure a long ride.
I hope this helps.