Heermann's Gull Overview, All About Birds, Cornell Lab of Ornithology

The Heermann's Gull, like many other gulls, frequently steals food from other birds. The Brown Pelican is a frequent victim. An adult Heermann's Gull is most likely to try to steal food from an adult pelican, and an immature gull is more likely to steal from an immature pelican.

The Heermann's Gull is the only North American gull that breeds south of the United States and comes north to spend the nonbreeding season. After breeding is over in July, the gull quickly comes north all the way to southern Canada. It heads back southward by December, and most breeders are at the breeding islands by March.

Perhaps as a result of the increasing populations in Mexico, several attempts have been made by Heermann's Gulls to breed in California. The first was on the island of Alcatraz. So far these attempts have been unsuccessful, but eventual successful nesting is expected.

The oldest recorded Heermann's Gull was a female, and at least 24 years old when she was caught and released in Oregon in 2009. She had been banded in Mexico in 1985.