Part of what makes gulls both amusing and exasperating to humans is their cleverness and opportunism when it comes to food. Across the gull universe, the diet is omnivorous. They’ll eat crustaceans, fish, insects and other marine organisms. They will also prey on the nests of other bird species for food.
A number of researchers have explored (and continue to explore) how much of this type predation on nests is affected by human intrusion. That is . . . beyond the immediate effects humans have on nest abandonment and nest failure, how does human involvement affect the numbers and presence of predators in nesting areas?
The Loon Preservation Committee noted that loon nest predation increased with the presence of human refuse. Another, older studied showed that human presence affected the vulnerability of cormorant eggs to gull predation. Even gulls themselves are subject to these vulnerabilities in their colonies.
In some cases, there’s actually a gull/nesting bird symbiosis. In a study done with Tufted Ducks in Finland researchers learned that some ducks will nest with aggressive gull species, and that nesting within the gull colony appears to provide more protection for the ducks’ nests.
Beyond their natural dietary considerations, gulls are obviously adept urban scavengers, too — scoring handouts of french fries and chips — or dumpster diving with fervor, even if the prize turns out to be shredded invoices.
Gulls appear to pay a physiological price for their fast-food habits. Heidi Aumen, a researcher at the University of Tasmania, studied the effects of junk food on gulls, specifically the silver gulls around Hobart. She found that gulls who ate a predominantly processed diet of bread, human snacks, and swiped pet food had higher cholesterol and glucose levels. And, the junk-food gulls were also tubby compared to their berry-and-invertebrate eating counterparts. They were 10 percent fatter, laying less viable eggs with smaller yolks.
You may have seen the two videos I’ve included at the end of this post . . . of gulls stealing food from cats and convenience stores. But, in light of Auman’s study, it’s probably more reassuring to see the juvenile gull in this photo series, working a mollusk for a hard-earned and healthy meal. (Well, I suppose the ‘health’ factor is debatable too, taking into consider the water source in the boat marina where this was shot.)
Two urban/suburban gull dining in modern ways, including the Dorito thief of Aberdeen: