The Dazzling Diversity of Gull Behavior
Editor’s Note: Thank you to our long-time volunteer, Joanna Chin, for preparing this wonderful piece and to her husband, Byron Chin, for the beautiful photography. A special thank you to guest photographer, Amar Ayyash as well.
When most people picture gulls, they think of gray and white birds squawking while soaring at the seashore, possibly also trying to steal food from beachgoers. While hanging out at the shore and pilfering food is surely part of the gull lifestyle, gulls are a wildly diverse group of birds with lots of different and fascinating behaviors! Here are just a few:
Bonaparte’s Gull: The only tree-nesting gull
While all other gulls nest on the ground, on rooftops, or on rocky outcroppings, the Bonaparte’s gull builds its nest in the branches of conifers in Canada and Alaska. Instead of wandering around on the ground like other young gulls do, their chicks stay in the nest until they’re ready to fledge. A picture of a Bonaparte’s gull in its nest can be found here: https://www.arkive.org/bonapartes-gull/larus-philadelphia/image-G120205.html
Swallow-tailed gull: The only nocturnal gull
While most gulls are diurnal, or active during the day, the swallow-tailed gull does all its hunting at night. This gull is endemic to the Galápagos islands, and its preferred food is squid. It makes sense that the swallow-tailed gull is nocturnal, as squid come to the surface of the water at night, where the gull can get at them (since gulls can’t dive well at all). The swallow-tailed gull has particularly large eyes to help it see better at night, and it has a white tip to its black bill, to help the chicks find it when they feed at night. This gull spends most of its day resting, and it has a white ‘eye spot’ on its lower eyelid, so from a distance you might think the bird is awake when really it is sleeping.
Heermann’s gull: Likes to steal a meal
Heermann’s gulls are renowned kleptoparasites: that is, they derive a large portion of their diet from fish they steal from other birds, usually brown pelicans. If you’re ever lucky enough to see a brown pelican plunge-diving for food off the California coast in the fall or wintertime, look closely: you’re liable to see Heermann’s gulls following them at close range. Sometimes they go so far as to land right on the pelican’s head, so they can reach into the pouch for a fish! Most gull species will steal food from another bird (or even another gull) given the opportunity, but some, like the Heermann’s gull, are particularly troublesome to other birds. The laughing gull also frequently kleptoparasitizes brown pelicans on the southern and eastern coasts of the USA.
California gulls: A different kind of fly catcher
California gulls enjoy eating brine flies, but they aren’t really maneuverable enough to catch tiny flies on the wing. Fortunately for the California gull, brine flies tend to alight in large groups on salty marshland shores. The gulls will run along the shore at full speed with their beaks open, snapping up flies as they go! This is referred to as “ram feeding.”
Large white-headed gulls are important predators of starfish here on the West Coast. They have two general strategies for eating these echinoderms. When they encounter a large starfish, gulls are more likely to flip it over and peck and tear at its underside. They have also been noted to take advantage of the starfish’s tendency to shed arms when attacked. A gull will bash the starfish against the ground until it breaks off all the arms, then swallow the arms and center separately. For smaller starfish, a gull might pick up the entire starfish and cram two or three arms into its bill. It will then push the remaining arms together with its gape as it forces the starfish into its mouth, making it into a compact rectangular shape that the gull eventually swallows. Different strategies, but same result: gulls are a major predator of starfish along the west coast.
As if identifying gulls weren’t challenging enough, with many species looking similar and multiple plumages within a species, they like to hybridize. One of the most common hybrids on the west coast is the Olympic gull: this is a hybrid between Western and glaucous-winged gulls. They are large birds with characteristics between the two: they’ve got pink to orange orbital rings (ring of colored flesh around the eye), speckled heads during winter, gray backs that are lighter than Western but darker than glaucous-winged gulls, and wingtips that are darker than their backs. Other gull hybrids found elsewhere in the USA are the Cook Inlet gull (glaucous-winged x herring), Great Lakes gull (great black backed gull x herring), and the Appledore gull (lesser black-backed gull x herring). There have even been hybrids between the laughing gull and ring-billed gull; two medium-sized gull species that look little alike, but do occasionally hybridize!
Home is where the gull is
Most gulls exhibit strong nest site fidelity; that is, they nest in the same spot year after year, particularly if they’ve been successful in previous years. They also exhibit strong pair bonds, with the vast majority of gulls mating for life, so long as both partners are still alive. Gulls have also been known to form same-sex pairs, with female-female pairs often raising chicks! This happens because gulls have a fairly high rate of “extra-pair copulations,” that is, while they maintain the pair bond with their chosen partner, they’ll sometimes mate with another bird. This helps keep genetic diversity high while maintaining all the benefits of stable pair bonds. If you frequent an area where gulls nest, pay attention: odds are very good that you will notice nests in the same spots year after year. If you do, it’s very likely you’ll be seeing the same individual birds year after year as well!
One good preen deserves another
When a bird cleans its feathers with its beak, this is known as preening. When one bird preens another, this is called allopreening. Allopreening serves both a social and a practical purpose: it is used to reinforce social bonds, and it also helps birds preen their head feathers and remove lice, which is difficult for a bird to do by itself. Interestingly, small gulls tend to allopreen, but the large white-headed gulls such as Western, glaucous-winged, and herring gulls, do not. They have on occasion been observed foraging for parasites on the feathers of another bird, but this is not the same as allopreening. The bird being foraged upon in these situations typically finds the other gull to be an unwelcome annoyance, whereas allopreening is an enjoyable activity for both birds involved. No one quite knows why large white-headed gulls don’t seem to allopreen, but it’s fun to watch the smaller gulls engage in this behavior.
Going around with gulls “dancing,” that is, tapping their feet quickly on the ground. The gulls aren’t really dancing, what they are doing is paddling for worms, also known as worm charming. There are a couple of theories as to why this works. Some believe the vibrations mimic the movement of a digging mole, a major predator of earthworms, so when the worms feel the vibration they come to the surface to escape. Others think the tapping of the gulls’ feet mimics rain, and worms naturally surface when it rains. Either way, gulls have figured this out, and many species perform this foot-tapping behavior. When the worms do surface, the gulls eat them. The New Zealand Department of Conservation has a wonderful video of red-billed gulls paddling for worms here: https://www.youtube.com/watch?v=kgw-Z0NQsW0
Now that you know some of the strange and wonderful things gulls do, keep an eye out next time you’re in an area they frequent! You never know what you might see these intelligent and beautiful seabirds do.