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Peregrine falcons (Falco peregrinus) are crow-sized raptors that usually nest on rocky cliffs in the wild. People have unintentionally created good nesting habitats for these birds – ledges on tall buildings, bridges, cellphone towers – and for this reason, there were 44 nesting pairs of peregrine falcons last year in Massachusetts. Most are on structures in urban areas. Peregrines have nested on buildings in Boston and Cambridge, including at MIT and Harvard, and the Tobin bridge in Charlestown. Today, only a few pairs nest on cliffs.
Industrious people have set up cameras at some peregrine nesting sites, including at the Custom House in Boston, so you can watch the processes of egg laying, hatching and the raising and feeding of falcon chicks. The chicks should hatch in early May. (A falcon cam in Lawrence gives perhaps the most close-up view.) Peregrine falcons mate for life. Most live for about 10 years, but one male at the Custom House territory lived until he was 17! He helped raised about 50 chicks.
Peregrine falcon pairs choose their nest site at the beginning of March, often returning to the site of the previous year. At the beginning of April, the female lays four eggs. One falcon sits on the eggs while the other hunts or rests nearby, but both male and female adults hunt to feed the chicks and the female tears off small pieces of meat to feed the nestlings. The 2-ounce chicks hatch in early May and double their birth weight in only five days! They now look like fluffy white snowballs. By three weeks, the chicks have grown to 10 times their birth weight. They leave the nest in mid-June. Watch for them as they practice flying near their nest sites.
By August, the chicks are completely independent and soon leave their home forever; young falcons search for territories of their own – one born in Boston set up a nest in Montreal from 2009 to 2017 – during their first fall and winter. Peregrine falcons in far northern places such as Greenland migrate south to Florida or even South America each winter, but the peregrines in our area do not migrate, because there is prey here even in winter. In our region, once they establish a territory, falcons remain year-round.
Although peregrine falcons live on every continent except Antarctica, they are not that common in Massachusetts. In the 1930s and 1940s, there were 375 nesting pairs east of the Mississippi, 14 of which nested on cliffs in Massachusetts. These birds were harmed when the pesticide DDT came into widespread use after World War II. It reduced the amount of calcium in the bodies of female peregrines, causing them to lay eggs with thin shells. The birds crushed the eggs while incubating them. The last nest from this period was in 1955 in Great Barrington. By 1966, there was not even one nesting pair on the entire East Coast.
In 1972, lawmakers banned DDT, and Massachusetts scientists began raising young falcons in captivity and releasing them into the wild, a process called hacking. At first, in the 1970s, these releases were unsuccessful. But scientists released young birds in 1984 and 1985 in downtown Boston that led to the first successful nest in 1987. Since that time, wild peregrines have hatched more than 1,150 peregrine chicks in Massachusetts.
Although “hacking” may sound like a modern word, falconers way back in the 1500s used the term. They placed falcon chicks in a wagon, called a hack wagon. They fed the young birds, and once they could fly, the birds would come and go as they pleased. The birds learned to hunt, and then falconers captured them and trained them.
This is essentially the same process that is used today: Adult falcons are bred in captivity. Scientists collect, incubate and hatch the eggs. When the chicks are about three or four weeks old, biologists place them in a wooden hack box in a desired location – often on a tall building or cliff. The hack box has grated windows and a locked door. The birds can see out, but they are safe from predators. Caretakers, who stay out of sight so the birds will not imprint on them, provide food. When the birds get bigger, the door is opened. The birds practice flying and hunting on their own, but the caretakers still provide food. The young birds come and go, eventually becoming independent.
Peregrine falcons usually hunt other birds in flight, especially pigeons. They are fast fliers and good at maneuvering at high speed. Still, it takes them on average about five tries to catch one bird as they fly high – up to 1,000 feet – and wait for a bird to fly by below. Then they flap to get their speed up and nosedive straight down. They can reach speeds of more than 200 miles per hour in their dives (called stoops). The peregrine strikes its prey hard enough to stun or kill it as it streaks past. Then it pulls out of its dive and turns to catch the falling prey. The most common prey are pigeons, starlings and blue jays.
Unlike many other birds, peregrine falcons do not build nests. Instead they find a cliff or ledge, and scrape out a shallow depression. Human-made nest boxes usually contain pea gravel, which allows the peregrine to make a shallow nest from which the eggs will not roll away.
Peregrine falcons have several adaptations that help them hunt, including a triangular notch on the edge of their upper beak called a tomial tooth. It helps the falcon sever the spinal cord of its prey, killing it quickly. Another: Each peregrine falcon nostril has a protruding small bony cone that breaks up air flow, allowing air to enter the nostrils more easily so the bird can breathe freely during its high-speed dives.
When mating season arrives, the male peregrine – two-thirds the size of the female – courts the female with dives and rolls. While the male and female are both flying, he passes food to the female, who rolls over and accepts it while flying upside-down!
It is just about time for peregrine chicks to hatch. Watch the falcon cams to see how the chicks grow from day to day.
Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
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