A Brown Pelican isn't likely to be very brown. The juveniles have a definite blue tinge, and an adults neck may be white, or chestnut brown. The colors intensify as breeding season nears. The Brown Pelican is the smallest of the pelicans, and the only one that catches fish by diving. The other pelicans fish while floating, sometimes using teamwork to herd fish into clusters.
The wingspans vary from 6 to 9 feet, none of them are small birds. I've seen pictures of a Brown Pelican swallowing a full grown Marsh Rabbit. No explanation accompanied the pictures, but Marsh Rabbits are strong swimmers, so a rabbit in the water is a definite possibility.