A sea of yellow: and over it, not inappropriately, a raft of seagulls, flying erratically, at some pace. The sea was a sea of rape, we were some miles from the actual sea: so what were these birds up to?

Answer: they were pretending to be swallows, flying about catching insects in their beaks. They're not terribly good at it - not as good as swallows. But they're good enough.

What kind of gull? Fair question; there are 46 species in my world checklist. These were black-headed gulls, the default gull, the gull

of rubbish tips and rooftops, of towns and fields and even, on occasions, the seaside. The gulls of everywhere.

They are the gulls of everywhere, but not because they are particularly good at anything. Rather, they are not bad at practically everything. They have more ways of feeding than practically any other bird. One of these is swallow-faking.

They also do low-flying, a few feet above the ground, scanning, and twisting and turning to drop on to edible stuff. They hover over hedges and trees and grab fruit. They hawk for insects low over the rape field, but they also do it much higher up, wherever there are insects.

They pretend to be marsh terns, picking stuff from the surface of the water. They lack the terns' consummate daintiness, but they manage. They also surface-feed, dipping their heads while swimming. They go in for scoop-feeding, running or swimming along with head submerged.

They also feed at the walk, striding out through grass and shallow water, or behind the plough, grabbing what they bump into.

They nick food from each other and from other species. They scavenge off rubbish tips, waste ground and sewage outlets: nothing is beneath them. They eat just about anything - worms, beetles, dragonflies, crabs, fish, chicks, eggs, mice, voles, moles, weasels, fruit, seeds, carrion bread, cheese.

They are endlessly adaptable, endlessly resourceful: and that is the secret of doing well in a world dominated by human beings. But they are not the sort of creature we admire. Humans tend to be touched by extremes of specialisation, by birds that have evolved for a single high and difficult purpose.

We love kingfishers, but kingfishers are lost without fish. We love swallows, but swallows are one-trick ponies and, increasingly, the way of the long-distance migrant is becoming unviable. We thrill to birds of prey such as the peregrine falcon, but this is a bird that has flirted with extinction in this country because it can live only one way. An albatross can't come in and hunt over the land - it has already made its choice by being born.

That is the way of the specialist. It is called the Tender Trap, the term for a species that has evolved brilliantly for a certain way of life, and then finds that humans have shifted the evolutionary goalposts. It is the strategy of all-your-eggs-in-one-basket: and it works supremely well so long as conditions remain stable.

But conditions are no longer stable. Humans are changing the world from top to bottom at a rate faster than evolution can take place. So mostly it is the generalists that profit: rock doves that become city pigeons. Rats, as always, live alongside us, supremely effective and, for the most part, invisible. And we tend to despise them. We call them pests and seek to control them. Instead, we admire the tenderly trapped specialists while putting them out of business.

Meanwhile, the despised seagulls get on with the business of survival. It's the only business they know and they're pretty damn good at it. No one likes them, they don't care.

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