Chimney Swifts are small, slender birds found across much of eastern North America. They are aerial acrobats known for their distinctive chittering calls and their ability to fly long distances at high speeds. An interesting fact about Chimney Swifts is that the young stay in the nest for an exceptionally long time before they are able to fly on their own.
Newly Hatched Chimney Swifts
Chimney Swifts build their nests on vertical surfaces inside chimneys, hollow trees, and other similar structures. The female lays between 3-5 white eggs which hatch after 19-21 days of incubation. The hatchlings are naked, blind, and helpless when they first emerge from the eggs.
For the first two weeks, the parents must brooding the hatchlings continuously to keep them warm. The hatchlings’ eyes begin to open at around 7-10 days old. At this stage, they are still unable to sit up on their own or lift their heads for more than a few seconds. Their wings are small stubs and their feet are unusable for grasping or perching.
The parents work hard to feed the ravenous young swifts a diet of insects gathered while flying. The hatchlings triple their weight in just two weeks. But they still cannot lift themselves up or move around the nest.
Three Week Old Nestlings
At three weeks old, Chimney Swift nestlings start to get some body control. They can sit up partially, shuffle around the nest a little, and can lift their heads for longer periods. Their wings have developed longer flight feathers, though the wings are still too small and weak for flight.
The nestlings start preening their feathers using their beak to distribute waterproofing oils. Their eyesight has improved and they watch the parents come and go from the nest. At this stage, they may beg and jostle for position to be fed first when the parents return.
In the second half of the third week, the nestlings begin “wing exercises”. They flap and flutter their developing wings within the nest, building strength. But at three weeks they still cannot get airborne.
Four Weeks Old
At four weeks old, Chimney Swift nestlings look much more like juvenile birds. They have the full set of flight feathers and their feet and legs are more developed. They can stand, shuffle, and climb around the vertical nesting surface.
The one thing they still cannot do is fly. Their wings are still underdeveloped and lack the power required for flight. Their wing “exercises” become more vigorous as they flap constantly to build muscle.
Even though they cannot fly, four week old Chimney Swift nestlings are often left alone in the nest while the parents go off to hunt for food. The stiffer wing feathers allow the nestlings to balance and hold their position better while the parents are away.
Five Weeks Old
At five weeks old, Chimney Swift nestlings look like fully-formed juvenile birds. Their wings are strong enough to provide some lift. In the protected environment of the nest cavity, the five week olds will hover and flutter in place while flapping vigorously.
By five weeks, they can climb using their feet and wings to move all around the vertical nest surface. When the parents return with food, the nestlings often flutter excitedly in anticipation of being fed.
Some nestlings may lift themselves into the air briefly inside the nest or perch precariously on the nest entrance. But sustained flight is still beyond their abilities. While close, five week old Chimney Swifts are still bound to the nest.
Six to Seven Weeks Old
Between six and seven weeks after hatching, Chimney Swift nestlings will take their first flights. At this advanced stage in their development, their chest muscles and wings are strong enough for sustained aerial maneuvering and flight.
On their initial flights, the fledglings will simply flutter down from the nest entrance to the ground. From there, they work on flying back up to the nest. These early flights help them refine control and build additional strength.
The Chimney Swift parents continue to deliver food to the newly airborne young. While first flights start around six weeks, it takes another one to two weeks of practice before the fledglings are adept fliers able to fly long distances and migrate.
Why Does it Take So Long?
Chimney Swifts take an unusually long time, six to seven weeks, to fledge compared to many other bird species. Here are some key reasons why Chimney Swift nestlings require such a long nesting period:
- They are born naked, blind, and helpless. They need time to grow feathers for warmth and flight.
- Their nests are vertical surfaces. Fledging requires developing feet and legs strong enough to perch and climb.
- They eat insects caught in mid-air. Extensive wing strength is required for aerial maneuvering.
- They are aerial masters from birth. Their agile flying skills take time to perfect.
- They have tiny feet that cannot perch. Wing strength must compensate for inability to rest.
Chimney Swifts have evolved as specialists in aerial living. Mastering the abilities they need as expert fliers requires a lengthy nesting period exceeding six weeks.
Fledgling Care
For one to two weeks after fledging, the Chimney Swift parents continue to care for and feed the young birds. The fledglings cannot forage on their own, so they still rely on their parents while mastering flight skills.
During this period, the parents lead the fledglings to suitable roosting spots for resting. The parents also call and encourage the fledglings to follow them as they forage for insects on the wing. This helps the young birds improve their flight endurance and agility.
Once the fledglings become adept at aerial feeding and flying long distances, they will no longer require the care of their parents. By seven to eight weeks of age, the juvenile Chimney Swifts can fly and feed independently alongside their parents.
Migration of Juveniles
One of the long flights that juvenile Chimney Swifts need to master is migration. Chimney Swifts spend the breeding season in North America and migrate to South America for the winter.
Juveniles that have successfully fledged and honed their flight skills over the summer join the adults on the long migration flights to the wintering grounds in the Amazon basin. The young birds fly along with the adults in large flocks on these marathon journeys.
The remarkable flight abilities of Chimney Swifts allow the juveniles to make migratory journeys stretching thousands of miles even though they are less than three months old. Their lengthy development in the nest prepares them for this immediate life on the wing.
Conclusion
Chimney Swifts have an unusually long nesting period of six to seven weeks before fledging their first flights. Their specialized aerial lifestyle requires extensive development before the young can take to the air and fly alongside their parents.
The naked, helpless hatchlings grow flight feathers, gain wing strength, and learn coordination inside the protected nest. After fledging, they continue to hone their skills with the support of their parents.
Within two months of hatching, the juvenile swifts are accomplished fliers able to migrate thousands of miles. The long fledging period equips the Chimney Swifts for a life of superb aerial mobility.
