Peregrine Falcon

Identification

A compact, deep-chested falcon with long pointed wings and a relatively short tail. Females are noticeably larger than males — the size gap is so wide that the sexes were once described as different species. Adults are slate grey above with a fine dark barring on the underparts, a crisp black helmet and a broad black cheek stripe that hangs below the eye like a drooping moustache. The eye ring, cere and feet are yellow. Juveniles are brown above and heavily streaked below, with a paler, less crisp face pattern.

Almost everything it eats is taken on the wing: pigeons, ducks, shorebirds, starlings. The classic attack is the stoop — a folded-wing dive from high above that ranks as the fastest recorded movement of any animal, exceeding 320 km/h in level flight measurements. It does not build a nest, but scrapes a shallow depression into a cliff ledge, a quarry face, or increasingly a skyscraper balcony, bridge girder or church tower, where city birds hunt the local pigeon flock. The alarm call is a hard, chattering series of kek notes.

The species was nearly erased from eastern North America by DDT and has recovered so completely that urban pairs are now routine. Look for it in fall and winter at coastal migration points and estuaries, where it flushes shorebird flocks, and scan tall city buildings and cathedral towers in spring for ledge-nesting pairs. Its level, stiff-winged flight — deep, quick beats followed by a glide — is a reliable cue even at a distance.

The stoop and how it hunts

Almost everything a Peregrine eats is taken in the air. The classic attack is the stoop: the bird climbs above its target, folds its wings into a teardrop, and drops at a speed that is generally accepted to exceed 320 km/h, making it the fastest recorded movement of any animal. The strike is often delivered to the wing or the back of the neck rather than to the body, and the prey is then retrieved as it falls.

Peregrines also use level pursuit, especially against pigeons and ducks, and they will work a flock of shorebirds by flushing it repeatedly until a straggler breaks away. A hunting pair sometimes coordinates, with one bird flushing and the other waiting above.

Nesting on cliffs and in cities

The species builds no nest. Instead it scrapes a shallow depression into a ledge, a quarry face, a bridge girder or a tall building balcony, and the same site may be used for many years. In towns, the birds effectively hunt the local feral pigeon flock, which is why urban pairs often choose the tallest building with the widest ledges.

Both parents incubate and both feed the chicks, and the female - noticeably larger than the male - does most of the brooding while the male hunts. Young birds leave the nest ledge before they can fly properly and spend a period on the ground or on lower ledges, which is the stage at which they are most vulnerable to traffic and to dogs.

Confusion risks

The black helmet with a broad cheek stripe hanging below the eye, slate-grey upperparts and finely barred underparts make the adult unmistakable in most of its range. Juveniles are browner above with heavy streaking below and a less crisp face pattern, and they are the birds most often mistaken for something else.

The usual comparison is with the Northern Hobby and the Eurasian Kestrel, both of which are much smaller and slighter. Flight style is a useful tiebreaker: a Peregrine's beats are deep, stiff and regular, followed by a flat glide, while a Kestrel hovers and a Hobby flies with faster, looser wingbeats and a more curved silhouette.

Where and when to look

Autumn and winter are the best seasons for watching hunting behaviour. Coastal migration points, estuaries and reservoirs attract birds that follow shorebird and wildfowl flocks, and a single Peregrine can empty a whole mudflat in a few minutes. Scan the horizon and the sky rather than the mud: the bird is usually up high, waiting.

In spring, look for ledge-nesting pairs on cliffs, quarries, cathedral towers and tall city buildings. City pairs are often easiest to watch, since they can be followed from a pavement with binoculars and often nest within sight of an office window.

Fieldcraft and conservation notes

Peregrine populations collapsed across much of Europe and North America in the mid-twentieth century because organochlorine pesticides accumulated in their prey and thinned the eggshells, so that eggs broke under the weight of the incubating bird. Bans on those compounds, combined with protection and with the provision of artificial nest ledges, allowed a recovery so complete that urban pairs are now routine.

The main thing to remember as a watcher is restraint at breeding sites. Disturbance at an eyrie can cause a bird to leave eggs or small chicks exposed, and in many countries nesting Peregrines are given special legal protection that makes approaching a nest without a licence an offence. Watch from a distance, and use a scope rather than walking towards the ledge.