Peter Rock, urban gull expert and a Research Associate at the UK’s University of Bristol, estimates urban gulls have been around for thousands of years, but they only began breeding on buildings after World War Two following the introduction of landfills on the outskirts of city centres.
Their numbers truly began to climb in the UK with the passing of the country’s Clean Air Act in 1956, which prevented landfill operators from burning rubbish on site.
“This was an open invitation to the gulls. They had a feeding bonanza,” says Rock.
Landfills may have encouraged gulls to nest in our cities, but with increasing anti-gull measures in place they aren’t the reason they have stuck around.
“Once urban populations start developing they realise it’s actually quite a comfortable life,” says Rock.
In the past 35 years, the number of gulls nesting in British cities has increased sharply.
Since the last national census of seabirds in the UK was conducted in 2000 the number of urban gull colonies has more than doubled from 239 to 512, says Rock. Cities offer gulls a safe environment free from predators and disturbance, warmer temperatures than the countryside and street lighting to enable foraging at night.
The key to the urban gull’s success is not necessarily easy access to food, adds Whitehead, as tracking studies have shown that gulls continue to forage quite a long way from urban areas. Rather, their numbers are being bolstered by rooftop nesting space free from predators.
“Herring gulls in urban areas are doing incredibly well. They’re producing more chicks each year so you’re seeing a real boom in population,” says Tony Whitehead, Public Affairs Manager of the UK-based Royal Society for the Protection of Birds (RSPB).
Despite their incredible population growth, the number of herring and lesser black backed gulls in urban centres is only a small proportion of the total population found nesting on coastal cliffs, offshore islands, by lakes and on moors. It is at these natural sites that gulls are faring much worse.
Rock’s research over the years has shown that in most cases gulls hatched in town will not recruit into a wild colony and vice versa.
What has developed, according to Rock, are two distinct populations that, despite encountering each other on migrations, don’t really mingle.
Rock reports that in the last 30 years, non-urban herring gulls have seen their numbers drop by 60 per cent, while lesser black back gulls have declined more than 30 per cent.
Whitehead says there are three major factors contributing to their decline; a lack of food (or food not being in the right place at the right time), disease and predation. The decline of the UK fishing fleet has also played its part.
“Bycatch isn’t available in the quantity it used to be and we know in other places around the world this is affecting the seagull population.”
Though Whitehead points out that the presence of trawlers may have artificially inflated population numbers in the first place.
So have seagulls abandoned the sea?
Rock says no. The majority of gulls are still nesting in natural sites and there are plenty of urban gulls to be found in towns and cities by the sea.
“They all move around. Usually herring gulls disperse off to the coast even if they have been breeding inland. It may well be that people who have been used to going to the seaside with hordes of seagulls have noticed that there is some decline,” says Rock.
shared via: www.bbc.co.uk/earth/story/20160708-have-seagulls-abandoned-the-sea
article: Kara Segedin
photo: Nick Upton/naturepl.com