Picture a seagull, and you’re likely thinking of the herring gull (Larus argentatus) – one of the larger (and louder) of the gulls around the coast of the UK. You might be imagining birds that hang around seaside towns harassing holiday makers, leading to tabloid headlines such as “Seagull terror: lock up your babies”. They’re ferociously adaptable, and can easily learn to exploit new food sources (such as tourists). But we know surprisingly little about what they get up to when they’re not scrounging for chips.

Bold, beautiful, and behaviourally fascinating, gulls are known to live up to 30 years; just imagine when you’re watching them that some individuals may have been born as long ago as the 1980s.

Although urban gulls in our towns are on the rise, gulls with a more traditional coastal lifestyle are declining rapidly. Urban herring gulls are harder to study than their wilder counterparts, because they use the town’s architecture as their own personal cliff face, and access to observe them is difficult. As gull researcher Peter Rock says, “houses are just small islands with steep cliffs”, but it’s much trickier to properly observe gulls on someone’s roof than it is on the side of a cliff.

To get around the problem of observing the birds, Peter and his colleagues used tiny GPS devices like the one in your phone or sat-nav. They strapped solar-powered GPS tags to the backs of four urban herring gulls – two males, two females – in the Cornish seaside town of St. Ives, UK. Each of these tags weighed just 18.5g, and were attached using a custom made harness. They then tracked each gull everywhere they went during the breeding season – when the parent gulls are building a nest and spending lots of time searching for food to feed their new chicks. Each of the four gulls was assigned numbers G4036 to G4039.

herring gull gps

One of the St. Ives’ breeding pairs. The Herring gull on the right is wearing the GPS tag. Photo by Peter Rock.

The results were surprising; they captured a portrait which showcased a wide variation in behaviours. Far from being townie menaces, these birds had complicated lives; more so than is commonly thought.

What do urban Herring gulls eat?

True to their perceived nature, all the birds spent a bit of time hanging around streets, but street-life was only a small fraction of their life. Instead all of the gulls strongly depended on farmland for getting food. Animal feed was a particular favourite, as was recently ploughed farmland (with all sorts of chopped up invertebrates and other animals exposed with the turned-over soil).

How far do they travel?

These four gulls covered a huge distance. Between them, they managed to travel 32,000 km throughout the summer. That’s three quarters of the circumference of the Earth.  But this total distance wasn’t evenly spread. G4036 and G4038 would routinely take long journeys of over 100 km; in contrast with G4037 and G4039, who never made such long trips. These more conservative birds were also predominantly land-based; perhaps making the occasional quick dash across water to get from A to B.

When do they sleep?

Two of the gulls would spend the nights at the colony, presumably sleeping. However, G4038 and G4036 were nocturnal sea-farers. G4038 spent some nights sleeping on the water (known evocatively as ‘riding the tide’). G4036 was mostly a night-gull; flying over the sea (sometimes as far as 80 km), then taking regular breaks on the water surface. In fact, neither of these two gulls seemed to have set themselves regular bed-times.

By the end of the study, only one gull was still wearing their GPS tag. One gull went missing, one was untagged by the researchers after technical issues, and the fourth gull removed their own harness and left it neatly next to the nest.

These were only four birds, but they showcase an amazing diversity of gull behaviours.  Whilst their traditional coastal counterparts are suffering from a population decline, studying the activities of these successful urban herring gulls may hold vital clues as to what’s going on. Peter and his colleagues are now planning to expand their research to study larger numbers of gulls in bigger, inland UK cities.

 

references

Rock, P., Camphuysen, C. J., Shamoun-Baranes, J., Ross-Smith, V. H., & Vaughan, I. P. (2016). Results from the first GPS tracking of roof-nesting Herring Gulls Larus argentatus in the UK. Ringing & Migration, 31(1), 47-62.

subscribe

Discover the story behind the research through the scientist’s eyes, subscribe to Biosphere digital magazine for access to in-depth articles that bring the natural world to life.