Cliffs with Offices In

There is a good chance there is a peregrine within a few miles of you, and a decent chance it is on a building.

Fifty years ago there was a serious question about whether the species would survive in Britain at all.

The collapse

Peregrines have never been popular with everybody. They kill racing pigeons, and during the Second World War they were killed under government policy on the grounds that they took carrier pigeons off the cliffs of the south coast.

But the real collapse came afterwards, and its cause was invisible.

From the late 1950s, breeding failures started being reported. Eggs were being broken in the nest, or not hatching. Numbers fell steeply across the country, and in southern England the bird effectively disappeared.

Derek Ratcliffe, working for the Nature Conservancy, ran the national surveys that established the scale of it, and then did the piece of work that identified the cause. He measured the shells of eggs in museum collections, going back through the nineteenth century, and compared them with contemporary ones.

The modern shells were thinner. Measurably, consistently, and starting at a specific date.

That date corresponded with the introduction of organochlorine pesticides — DDT and the cyclodiene seed dressings. The chemicals accumulated up the food chain and concentrated in a predator at the top, interfering with the bird’s ability to lay down calcium. The peregrines were crushing their own eggs.

The demonstration depended entirely on the fact that Victorian collectors had taken thousands of eggs and museums had kept them.

The return

The chemicals were restricted from the 1960s and withdrawn over the following years, and the peregrine recovered — slowly, then not slowly at all.

And then it did something nobody had predicted. It moved into cities.

The reason is architectural. A peregrine nests on a ledge on a cliff, high up, with a clear drop in front of it for the stoop. It does not build a nest; it scrapes a hollow in whatever is on the ledge.

A cathedral tower is a cliff. So is a power station chimney, a tower block, a bridge pier, a multi-storey car park and a disused mill.

And a city offers something a Welsh sea cliff does not: an unlimited, year-round, immobile food supply in the form of feral pigeons, which are themselves descended from rock doves and are nesting on the same artificial cliffs for the same reason.

Where they are

Salisbury, Norwich, Lincoln, Chichester, Derby, Wakefield, Leicester. Battersea Power Station, Tate Modern’s chimney, the Houses of Parliament. Cooling towers, gasholders, and a substantial number of anonymous office blocks whose tenants have no idea.

Many sites now have a nest platform installed by a wildlife trust and a camera on it, and the cathedral peregrine webcam has become a small English institution.

The birds do not care. What they are responding to is height, a ledge, and a clear approach.

It isn’t that the peregrine adapted to cities. Cities happened to become suitable for it — we build tall vertical structures with ledges on them for entirely unrelated reasons, and we happen to maintain an enormous population of the exact prey species it evolved to catch.