Herring gulls have wrecked many a seaside picnic, pouncing on unsuspecting people trying to enjoy a Cornish pasty, a sandwich or a bag of chips.
But a study from the University of Exeter suggests gull chicks prefer seafood even after being raised on a diet of the sort of scraps found around humans.
Scientists studied herring gull chicks that had been rescued after tumbling out of nests in roofs in towns across Cornwall. While they were in captivity, they were given either a “marine” diet consisting of mainly mackerel, sprats and mussels, or an “urban” diet, mostly bread and cat food.
Every few days the chicks were presented with a choice of four foods in different bowls, to test which they preferred – and all of them strongly favoured fish. “When fish is available they clearly prefer it,’ said the lead author, Emma Inzani, from the Centre for Ecology and Conservation at the University of Exeter’s Penryn campus in Cornwall.
The team worked on the presumption that because the chicks came from rooftop nests they would have been raised mainly on an urban diet. “Our results suggest that, even when reared on an urban diet of foods found only around people, these chicks might be unlikely to seek out urban foods as adults,” Inzani said.
Herring gulls are often seen as a pest in urban areas, where they scavenge for dropped food and in bins, and sometimes take food from people, but they are considered a species of conservation concern and, like all wild birds, their nests and chicks are protected by law.
Inzani said a combination of reduced fish stocks in UK waters, coupled with abundant and easy-to-access food waste in towns, may mean it is not as profitable for gulls to spend a lot of energy going out to sea to forage.
In the study, 27 chicks had access to food all day, but half had urban food for 80% of the day and seafood for 20%, while the other half of the chicks received the opposite diet.
When presented with all four foods together on days five, 10, 15 and 35 of the study, both groups consistently favoured fish – and even those that tried the bread rarely ate much of it. A video released by the team shows a chick heading straight for the mussels and gobbling them up, then trampling over the bread to get to the seafood and ignoring the cat food.
Another of the scientists involved in the study, Neeltje Boogert, said: “Animals can live and exploit urban areas for human food waste. However, this does not necessarily mean they’re thriving or that they prefer this food, rather than making the best of a bad situation.”
The chicks were apparent orphans who could either not be reunited with their parents, placed back into their nest, or whose exact origin was unidentifiable. All were brought into the rehabilitation facilities within 24 hours of rescue from towns across Cornwall, the majority from residential roofs.
When they were released back into the wild, chicks in the terrestrial group were significantly lighter than their fish-eating counterparts.
The report says the findings that the chicks were not keen on bread was at odds with a 2015 study on black-headed gulls. It found urban-dwelling black-headed gulls were more likely to go for bread over fish, while gulls in rural areas exhibited the opposite preference.
“An increased reliance on anthropogenic foods such as bread may emerge later in life, perhaps when older individuals experience lower foraging returns from attempts to feed on dwindling marine prey,” the report states.
It adds that investigating the development of individual food preferences of animals is important to understand and predict how species may cope with increasing urbanisation and the climate emergency.
The paper, published in the journal PeerJ, is titled: “Early-life diet does not affect preference for fish in herring gulls (Larus argentatus).”
