Adults have a medium gray body, blackish-gray wings and tail with white edges, and a red bill with a black tip.

[1] Some birds exhibit strong site fidelity to their nonbreeding territories, including a one-legged gull who resided for 17 years at the Loch Lomond Marina in San Rafael, California.

In June 2018, one of the colony's main nesting sites, the Seaside McDonald's, was destroyed by a drunk driving crash.

[6][8][9][10] Heermann's gull eats small fish, marine invertebrates, lizards, insects, refuse, and carrion.

The success of the colony in any one year is dependent on the availability of prey and this is related to the ocean temperature changes brought about by El Niño.