Interesting Information on the Peregrines and their Nesting Behaviors
Where is the nest? The falcons on this camera are nesting on the tenth floor of the north side of the Maricopa County administration building in downtown Phoenix, Arizona.
How can you tell the difference between the male and female peregrine? Females are larger and more powerful than males. They have a mottled or streaked chest washed with salmon color. The male has an unmarked light-colored chest and s looks more slender. Both adults have dark blue-gray wings and backs barred with black. Their undersides are pale, and their heads have a dark crown with a black stripe on each cheek. Their eyes are large and feet and legs yellow.
Do they mate for life? Peregrines typically keep the same mate for life. However, if a member of the pair dies, the surviving falcon will pair with another bird.
Do the adults migrate? Some peregrines migrate and some don't, it depends on their geographic location. The Phoenix peregrines apparently do not migrate.
What do peregrines eat? Their prey consists mostly of birds including ducks, pheasants and pigeons. Based on prey remains, falcons find many different birds in urban surroundings. Bats are also taken on occasion. Prey remains and observations on this pair have revealed mourning doves and pigeons are their primary prey. Interestingly we also found the remains of a burrowing owl at the nest site.
How do peregrines capture their prey? Prey is caught on the wing. Peregrines swoop down on their prey from above, using great speed (over 60 mph), the falcon delivers a powerful blow to its prey with a half-closed foot (like a fist). It retrieves the stunned or dead bird either in mid-air or after it falls to the ground.
How long do peregrines live? Peregrines live to be 12 to 15 years old. However, the mortality rate for young falcons is about 60%. This means that approximately 6 out of every 10 falcons hatched will die in its first year of life.
February – Early in the month individual peregrines visit the nest box for brief periods, often vocalizing when they do. As the month advances, the pair begins to visit the box more frequently and together, exhibiting various courtship behaviors such as sprawling on the bottom of the nest box and calling. When a single falcon is present in the box, it might call vigorously to its mate, enticing it to visit the nest box. The birds also often clean the nest box, removing feathers or other debris with their beaks. One or another of the pair can often be seen to lean forward, pushing with its talons, to use its breast to form the substrate into a bowl (“scrape”) where the eggs will be laid or dig in substrate to form a depression. Scraping is part of courtship.
March – Courtship behavior continues. The male and female frequently visit the nest at the same time, leaning toward each other in a bowing fashion. They may also be seen to exhibit other bonding behaviors. The birds continue to work on the scrape and clean up around the nest in preparation for egg laying. Eggs should appear sometime toward the end of his month. The falcons typically lay between 3 or 4 eggs, spaced 1-3 days apart. They don't start incubating until they've laid their next to last egg. Both adults take turns incubating the eggs, which hatch in about 30-34 days after incubating starts in earnest. During incubation, prey is brought into the nest box by the foraging adult for the pair to share. The pair exchanges incubation duties about every 30 minutes to an hour. During incubation eggs are repositioned and rolled, this often occurs after an incubating exchange.
April – This is the incubation month. One of the pair will be attending the eggs most of the time. The eggs may be left alone for very brief periods during prey exchanges or changes in incubating shifts. The parent out foraging will bring prey to the parent on the nest. Incubation continues for another 33-35 days.
May-June – The chicks typically hatch in early May. A falcon chick is called an eyass. Both adults tend to the young; feeding and keeping them warm until they are about 10-11 days old. After that, both adults will need to leave the young unattended to hunt in order to meet the needs of the quickly growing eyass’. Nestlings eat a lot and grow quickly, doubling their weight in about six days. By the time they reach three weeks of age, they will be ten times larger than they were at birth.
The months of May and June are filled with activity at the nest. Adults bring prey to the box about every hour and the growing young preform wing-strengthening flapping exercises and explore the nesting area, often venturing out onto the ledge of the building. The young are capable of flight at about 42 days of age, though these first attempts are awkward and may be better described as controlled crashes. At this time the adults may attempt to coax the youngsters out of the box on trial flights. Young often stand on the edge of the box, acclimating themselves to the outside environment. At the end of the nesting period the adults stop directly feeding the young (bringing prey inside the nest) to encourage the young to fly and leave the nest. Once a young bird has left the nest it is considered fledged. The adults continue to provide prey the young during the fledging period in addition to teaching them how them how to hunt.
July – Flight and hunting lessons continue as the young falcons prepare for life on their own. Towards the end of July and into early August, the adults will start to encourage the young falcons to disperse and find their own territory.
Why do the eggs hatch within a few days of each other when they are laid as much as eight days apart?
How long is the incubation period?
Why don’t the adult peregrines sit on the eggs all of the time?
Do all of the eggs hatch?
Do males help incubate the eggs?
Can a parent feel movement inside the eggs?
Do peregrines eat their own eggshells?
Is it normal for the chicks to be left unattended for extended periods of time?
How long do young peregrines stay in the nest?
How do the chicks develop?
Where do peregrines nest? In the wild peregrine falcons nest on remote ledges, cliffs and canyon walls, where it is difficult for predators to reach them. Cliff nests are generally located under overhangs or on ledges with vegetation which afford some additional shelter from the elements. Peregrines do not gather nesting material. Instead, they make a shallow depression in the existing debris with their by scratching with their feet. This hollow is called a scrape
Why do peregrine falcons nest on buildings? Falcons have adapted quite nicely to urban areas. City skyscrapers with their tall vertical faces and ledges emulate the conditions found on cliff faces and in canyons. Wildlife biologists frequently provide a gravel-filled nest boxes or trays for city-nesting birds to use.
>How much time elapses between eggs being laid? Eggs may be laid anywhere from eight hours apart to as much as seven days apart.
Why do the eggs hatch within a few days of each other when they are laid as much as eight days apart? Incubation starts in earnest when the last egg is laid, so most eggs hatch within a few days of each other. This is referred to as asynchronous hatching. Older chicks sometimes bully smaller younger siblings, keeping them from feeding. Delayed incubation facilitates close hatching dates and enables all the chicks to fledge within a few days of each other.
Why don’t the adult peregrines sit on the eggs all of the time? Before incubation begins the falcons may be observed standing in or near the nest guarding the eggs. Once incubation begins, one of the adult falcons is usually sitting on the nest, however during warm weather or food exchanges between the male and female, the eggs may be left unattended for short periods.
Do all of the eggs hatch? Sometimes there is "egg failure" which can result from a number of factors including infertility, breakage, or weather. The female may push an egg that has failed to the side of the nest box. If an entire clutch is lost, the female may attempt to re-nest several weeks later, often in a different location.
Do peregrines eat their own eggshells? There is nothing to suggest that peregrines exhibit this behavior. However, adult peregrines have been seen nibbling at the shells to break them up rather than to eat them.
Is it normal for the chicks to be left unattended for extended periods of time? Yes, but for the first few weeks after hatching the chicks are brooded almost constantly. After approximately 2-3 weeks they no longer need constant brooding and are often left alone. The adults typically perch nearby, often for extended periods.
How long do young peregrines stay in the nest? Approximately forty to forty-five days after hatching. The downy white feathers the nestlings have when they hatch are replaced by juvenile feathers in about three to five weeks. At about 6 weeks of age, young falcons will make their first attempts at flying. After they fledge (take their first flight) they are referred to as fledglings and are still dependent on their parent’s care for another four weeks or so.
How do the chicks develop? See the Canadian Peregrine Foundation’s Peregrine Falcon Development – Age Guide chart.
Does the light on the camera at night bother the falcons? No. The light is an infrared (IR) light and is not visible to the birds. Viewers can see the birds after dark, but the birds are not disturbed by the light. A special filter makes the light visible to camera. IR lighting is widely used by biologists to study wildlife at night…notice the image is black and white, not color, that is typical for IR images. This makes the rust-colored eggs look white in the nest at night.
The male’s often has his left eye is closed, is it OK? It appears one of his eyes is bothering him. The eye does not appear damaged, though he does tend to keep that eye closed a lot. The bird is now more than 10 years old. The maximum life expectancy for peregrine falcons is about 15 yrs. He is an old bird. If you watch long enough, you will see him open the eye. The male seems very capable in capturing prey so apparently he still sees well through that eye.
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