Gung-ho gulls gather momentum

GULLS, the entrepreneurs of the bird world, start new businesses whenever opportunities arise.

Town dumps, for example, were once the preserve of red kites. When the kites were driven out, scavenging ‘seagulls’ moved in. Then they headed into the countryside to follow the plough, scooping up worms and creepy crawlies from the overturned soil. Such gung-ho behaviour paid off; there are more gulls alive today than there ever were.

Fifty years ago, gulls began their most audacious project yet; nesting on roofs and chimneys in towns and cities. Their business plan listed the advantages. Humans, it declared, are dirty animals which leave discarded food wastes lying about — rich pickings for scavengers.

Built-up areas are lit at night, allowing more time to forage and feed. There’s unlimited, relatively sheltered, roof-space on which to nest. Temperatures are several degrees higher in cities than on the windswept coastal outcrops where gulls traditionally breed. Predators, apart from the odd cat, are few; eggs and chicks are less likely to be taken. Nesting in towns appeals to two species in particular, the herring gull and the lesser black-backed.

While overall numbers of both have declined recently, their urban colonies have expanded. Gulls now breed in over 400 towns in Britain and Ireland.

The new arrivals are not popular, however, with human residents. Gulls are messy nesters; stains of white droppings spoil the appearance of buildings. Parent gulls become aggressive when they have eggs or young, swooping at anybody who ventures too close. Actual contact is rare but angry gulls occasionally strike an intruder, drawing blood and providing fodder for tabloid newspapers. These are noisy birds disturbing lazy-head citizens who waste hours of morning light lying in bed. Nobody wants to live close to gulls.

Given these difficulties, how well are urban gulls faring? Are town nests as productive as traditional coastal ones? Is the life expectancy of a city gull equal to that of an islandnesting one? Ornithologists Peter Rock and Ian Vaughan decided to find out. The results of their research appear in the current edition of the journal Ringing & Migration.

Bristol has a large gull colony; about 2,500 pairs nest 11km from the coast. Chicks have been ringed there since 1982. The metal rings, fitted about 14 days before the birds fledge, are light and cause the wearer no discomfort. Each carries a serial number and the message ‘Inform British Museum London’. Anyone finding a ringed bird will, hopefully, report it and, if enough are found, life-expectancies can be estimated.

Rock and Vaughan recorded 500 sightings of 191 individual herring gulls which had reached the age of four and 1,373 sightings of 505 adult lesser black-backed gulls. By tracking the birds, they were able to calculate survival rates. During the early 1990s, they found, more than 90% of adult herring and black-backed gulls survived from year to year.

By 2007, the re-sighting rates had fallen but survival was still at least 70%. The decline, however, may be more apparent than real; a missing bird is not necessarily dead; it might have left the colony. Urban redevelopment and the hostility of human residents may be forcing gulls to leave.

Comparisons with wild colonies show that mature Bristol gulls have survival rates similar to their more traditional cousins. The study, so far, has concentrated on adult birds. Do as many chicks fledge from a city nest as from a coastal one and how many youngster reach adulthood four years later? The researchers will try to answer these questions in the next phase of the project.

* Long-term estimates of adult survival rates of urban herring gulls and lesser black-backed gulls. Peter Rock and Ian Vaughan. Ringing & Migration 28.