PEREGRINE FALCON (Falco peregrinus)
Names and terminology
The genus name Falco comes from the Latin falx, which means sickle-shaped. It is often assumed that this refers to the shape of a falcon’s wings in flight, but others believe that it was meant to describe the shape of their talons or beaks. The species name peregrinus is derived from the Latin word meaning wandering, from which the word “pilgrim” also originates. It refers to the peregrine’s habit of not only making long migrations, but also of dispersing widely from their birth site to find nesting territories. Both males and females are commonly called falcons, although falconers refer to males as tiercels and only females as falcons. Chicks are called eyases, and the nest site is called an eyrie (also spelled aerie).
How to recognize a falcon
Falcons belong to a group of birds known as raptors, or birds of prey. The majority of these birds share some basic characteristics, most notably that they have large strong feet and sharp talons for holding on to their prey, and sharp hooked bills for tearing at flesh. They also often have excellent eyesight, and most are highly skilled fliers. Their long, pointed wings, and their medium-to-long but generally narrow tails can distinguish falcons. As a result, they have quick and powerful wing beats and are much more agile than other raptors, but on the other hand they cannot soar as well as species with broader wings. Falcons are also unique among raptors in that they have a notched beak (which looks like a little tooth on the upper mandible) that they use to help them sever the spinal column of their prey. Behaviourally, falcons differ from other raptors in a few ways. Most notably, they do not build their own nests. Rather, they use tree cavities, rock ledges, or stick nests built by other raptors. Also, when excited, falcons typically bob their heads and pump their tails up and down. Other raptors may also move their tail when excited, but tend to wag it from side to side instead.
While peregrines are rare, they are remarkably widespread. In fact, the peregrine has a more extensive natural global range than most other birds. Peregrines can be found on every continent except Antarctica. Presently, the breeding range is restricted to most of Canada, Alaska, the western states, and scattered sites in the eastern United States.
Unlike many raptors, which avoid crossing large bodies of water, peregrines have often been seen far out at sea, catching and eating seabirds while on the wing, and even resting at times on ships. Studies on a few individuals from Canada and Greenland have suggested that peregrines spend roughly one month flying south, and another month coming back north in the spring. On average, they leave their breeding grounds in September and return in March. Northern nesting birds typically leave earlier and come back later, while birds which breed further south may linger on their breeding territories longer and return sooner. Many of the urban peregrines (city dwellers) in eastern North America have now chosen to not migrate at all anymore – they just stay in their breeding territory all year long. This is presumably because unlike in traditional natural nesting areas, the food supply in cities is reliable throughout the year, and thus there is no need for the peregrines to migrate.
Peregrines generally mate for life, but will readily accept a new partner if their mate dies. Migratory pairs may separate for the winter, while resident peregrines generally maintain pair bonds throughout the year. In either case, most peregrines go through courtship rituals every spring. Males court the females with aerobatic flights and repeated calls. Courtship feeding is often observed, where the male will catch prey and present it to the female. This strengthens the pair bond, and also gives the female the extra nutritional boost she needs to lay healthy eggs, since she is too heavy to hunt efficiently on her own just prior to laying the eggs. Although pairs commonly stay together for many years, the relationship between couples often appears to be not too friendly. Females are normally dominant over males, and can be quite aggressive toward their partners. Often they will take food from the male, or chase him away from the nest. For his part, the male often approaches his mate cautiously and bows in submission to her.
Once the pair bond has been established, the next priority is to select a nest site. The male chooses several potential nest sites, and shows these to the female. She then decides which one of these she likes the best, and that becomes the nest. In some cases, pairs will alternate between two or three closely spaced nests over a period of several years, but more often a pair will use the same nest again and again, provided that they nest there successfully.
Peregrine eggs range from creamy pink to reddish-brown in colour, and are 53 mm (2.1 in) long (slightly smaller than chicken eggs). An average nest contains three or four eggs. Young pairs often only have two eggs in their first breeding season, and then increase to three or four eggs in subsequent years. Some peregrines regularly produce five eggs, and rarely as many as seven. The demands of feeding hungry growing chicks makes it difficult for a pair to successfully raise more than four chicks, although if food is plentiful they can sometimes manage to feed five. The eggs are usually laid every other day, and are left mostly unattended until the last or second-last egg has been laid, at which point incubation begins.
For peregrines, incubation usually lasts 33 to 35 days from the date the last egg was laid (or the second last, if that is when incubation began). The eggs generally hatch on successive days, but occasionally two hatch on the same day, or a day or two passes between hatching. During the incubation period, the eggs are rarely left uncovered for more than a minute or two, although on very warm days the adults may stay off them for somewhat longer periods. Typically the female sits on the eggs throughout the night, and also for much of the day. The male takes over for several short shifts through the day so that the female can get away and hunt for herself. As a result, the female usually does about three quarters of the incubation herself, while the male contributes the rest. In the last couple of days before hatching the female often becomes reluctant to leave the nest, and chases the male away if he offers to take over incubation.
Peregrine chicks grow up very rapidly. By the time they are six weeks old they have already grown to full adult size, and are starting to fly. As the chicks develop, the parents allow them to become increasingly independent, and each week the appearance and behaviour of the chick’s changes noticeably:
There is a great deal of variation in the time at which peregrine chicks leave the nest for their first flight. On rare occasions they take off as early as 33 days after hatching, while others linger for over 50 days. The majority, however, leave between 38 and 45 days. Females generally stay in the nest longer, because they are heavier and need longer to develop and strengthen the flight muscles needed to carry them safely. In the days before fledging, the chicks often spend hours on end perched looking over the edge, and flapping their wings, but seem to not be able to get up the nerve to go. Often the parents seem to try to encourage their young ones to take off, by flying past the nest carrying food in their talons, and by withholding food from the chicks for most of the day.
Some studies suggest that peregrines have an average life expectancy of only four to five years, while others indicate that the range is as high as 10 to 12 years. Captive birds frequently live even longer, and there are also records of a few wild birds, which have nested for as many as 17 consecutive years. Although some peregrines have been known to breed when only one year old, they are generally considered to be mature at two years of age. Females will typically continue to lay eggs once a year until they die. The only time that a female would lay more than one clutch of eggs in a year is if the first eggs are lost or damaged before hatching or the chicks die in their first few days.
Food and hunting
Peregrines generally hunt by diving on their prey from great heights. They fold their wings to their sides and go into a stoop (dive straight down), attaining speeds of up to 320 kilometres per hour (200 mph). They are the fastest living creatures on the planet, next to humans in airplanes or race cars. It was long thought that peregrines hit their prey in midair with their feet clenched like a fist in order to knock out their victim. However, it has been discovered that they keep all of their toes fully extended, and strike either with their talons or with the back of their forelegs. The impact is usually forceful enough to kill the prey instantly, and the peregrine either stoops down to catch it as it tumbles, or picks it up off the ground where it lands. In cases where the initial blow was not enough to kill the prey, peregrines usually bite the neck of the victim to finish it off. Peregrines have extremely good eyesight, even in poor light, and often do much of their hunting at dawn and dusk, while remaining at rest during the heat of the day. Peregrines, as well as many other predatory species, can eat large quantities of food in one sitting, which is to their advantage because they never know when they will get their next meal. Peregrines can, in one sitting, eat a meal weighing as much as one quarter of their own weight. Additional food is usually stored in caches to be returned to at a later time when fresh food is scarce. A typical peregrine family (two adults and three young) eats roughly 225 kilograms (500 lbs) of food per year.
Prey of choice
Most peregrines eat birds almost exclusively, although fledglings are often observed chasing after and catching large flying insects such as dragonflies. While on migration, many peregrines hunt primarily shorebirds. In natural areas, Peregrines often nest near wetlands. As a result, their diet consists largely of ducks, grebes, rails and a variety of wetland songbirds such as blackbirds. In urban areas, the peregrines take advantage of the abundance of city birds such as pigeons, starlings, and sparrows.