Seagulls bring a hint of Hitchcock horror to Cadiz

The Spanish port of Cadiz is waging war on gulls that have taken command of the skies around Spain's south-western tip. An emergency plan adopted by the Andalusian regional government has seen the destruction of 15,000 gulls' eggs, removal of nests and shooting the troublesome invaders where necessary.

The thousands of yellow-legged gulls, whose numbers have risen sharply in the past five years, damage buildings and dive-bomb people on beaches and in food markets, officials say.

Although it is the most common southern European gull, the yellow-legged variety (Larus michahellis) was rare along the Cadiz coast until recently. However, its strong survival instinct has enabled it to colonise a new habitat. The voracious bird eats almost anything, finding its food on the marshy shores of the Bay of Cadiz Natural Park, around fishing ports and at two rubbish disposal plants. It preys on other birds such as stilts, avocets and terns, and destroys the nests of others. It carries microbes, damages vegetation and poisons water. This, officials claim, justifies their extreme eradication measures.

"We face difficult situations in markets, where the gulls become aggressive in their pursuit of food, and in school playgrounds, where children's lunchboxes are raided," said a regional environment spokeswoman, Gemma Araujo. "We need more co-ordinated action."

About 5,300 nests containing 15,000 eggs have been destroyed but the gulls swiftly re-establish lost ground. Officials tried to be more cunning by dunking eggs in paraffin – which kills the embryo but leaves the egg warm. The gull then continues to incubate a chick that will never hatch, delaying the moment when it builds a new nest.

The next step was to clear nests from rooftops and shoot gulls that flocked to the rubbish dumps.