Black-capped chickadees are a beloved fixture at the Arboretum, one of our common year-round residents and the state bird of Massachusetts. Visitors can easily observe them flitting through the branches, often in small groups during fall and winter and in pairs during spring and summer.
In Boston, black-capped chickadees begin searching for nest cavities around mid-March, weeks before most migrant species return. By mid-April most are building nests and by the first week of May the females typically are laying eggs. The nestlings begin hatching two weeks later, grow rapidly, and start fledging in early June.
Each year, the Arboretum’s NestWatch volunteers follow this process by monitoring over a dozen “chickadee tubes” installed throughout the landscape. These nest tubes are variations on a design by Dr. Desiree Narango and are specifically designed to attract and accommodate chickadees. The following photos depict the life stages of young black-capped chickadees in several different nest tubes throughout the grounds.
A typical Arboretum “chickadee tube”, a derivation of a design by Desiree Narango. The main differences are an overhanging roof to prevent nest predators from reaching into the entrance hole and a recessed wooden floor to reduce water absorption through the venting holes on the bottom. The 1 1/8 inch entrance hole allows only black capped chickadees and house wrens to enter. The tubes are filled to the entrance hole with aspen wood shavings in late winter, as chickadee’s seem to prefer nest boxes which they can excavate themselves.
Arboretum NestWatch volunteer Mitchell Stokes inspects a nest tube. Our team of NestWatch volunteers monitor assigned nest boxes and nest tubes every 3-4 days during the breeding season, gathering data on the nesting process of the birds which use them. The data is submitted to the Cornell Lab of Ornithology’s NestWatch database, advancing the study of bird breeding behavior and helping us track nest usage at the Arboretum.
A pair of black-capped chickadees has excavated the aspen shavings that once filled the entire tube. Different pairs excavate to different depths, although the average is 6-7 inches below the entrance. This may be from a natural inclination to build their nests beyond the reach of common nest predators, such as raccoons and possums. The area below the entrance in this photo was purposefully rough sanded and scratched during construction, in order to provide easier gripping for the exiting birds.
Black-capped chickadees construct their nests with moss, inner tree bark, and soft grasses. They line the nest cup (where the eggs will be laid) with a soft layer of animal fur. These cozy nest materials are necessary in order to keep their eggs and nestlings warm through the chilly spring weather. Female chickadees, like most songbirds, lay one egg per day, usually in the morning. To keep them hidden or perhaps to keep them warm, the female initially hides her eggs under a plug of animal fur whenever she leaves the nest. Clutch sizes average between 6-8 eggs and the female begins incubating once she has laid the final egg (or occasionally the day before). To facilitate incubation, the female loses a patch of feathers on her breast, called a brood patch. When she sits on the nest, her feathers part and the bare skin of her brood patch presses upon the eggs. Even though the skin-on-egg contact increases the heat transfer between her body and the eggs, she still must incubate them for approximately 12 days before they hatch.
1-3 Days Old: Black-capped chickadee nestlings, like most songbird young, are altricial (born naked and blind). This is opposed to the fully feathered and mobile precocial nestlings of most ground nesting and aquatic birds, such as chickens, geese and ducks. From now until they leave the nest, these young birds are entirely dependent on their parents; without them, they will die. During the first few days they require constant attention. The female spends time in the nest brooding to keep them warm while the male brings them food. Both parents remove their waste, conveniently contained in fecal sacks that can easily be picked up and carried away.
4-8 Days Old: Feathers begin to fill in along the wings, back, and tail, but patches of bare skin can still be seen and the eyes remain closed. The female spends more time out of the nest gathering food and the nestlings grow strong on a protein rich diet of insects (especially caterpillars). They nestlings have huge white and orange oral flanges extending from either side of their small beaks. These help the adults locate and feed them in the dark of the nest.
9-11 Days Old: Their eyes are now open and they can see the world around them. Their skin is almost completely covered by feathers. The iconic black and white pattern begins to grow in. When blind, the young typically beg for food even when a human opens the tube to check on them (see the brave, hungry nestling in the previous photo). With sight comes wisdom, and they now all silently hunker down when disturbed.
12-14 Days Old: The nestlings now resemble their parents. Their oral flanges are receding and their feathers have developed. Instead of waiting passively, they now flap their wings, noisily call for food, and perch in the nest entrance to monopolize the adults’ attention. At twelve days old, the nestlings are now strong enough to fly from the nest if a predator attacks. However, since they lack fully developed flight feathers, they would not be able to fly well or far and face the danger of starvation or predators on the ground. As a result, it is best not to visually check chickadee nestlings once they reach 10-12 days old. That said, the nestlings in this photo are about 14-15 days old. They were checked due to concerns that the consecutive days of rainy weather in early June had compromised the nesting tube (fortunately, it had not). Despite being bothered, all seven young in this photo remained in the tube for another few days before successfully fledging.
14-18 Days: An empty nest! One by one, the young chickadees flap up to the entrance hole and flutter out to nearby branches and shrubs. Although they can now fly short distances, they remain dependent upon their parents for food. The adults continue feeding them, somehow keeping track of this constantly moving clan. After a couple of weeks, the young birds have learned to find food on their own. They either fly away from their parents for good or are purposely left behind by them. Adults at this point require time to regain strength lost from the energy intensive task of raising young. Just 14-18 days from naked and blind nestlings to fully capable and flying young birds.
Juvenile chickadees face long odds. Although the average lifespan of a black-capped chickadee in the wild is about 2 years, it is likely that most of this year’s fledglings will not survive the next few months. However, if they learn quickly to avoid predators, survive disease, and find enough food to live through the hard winter months to come, we may see these same birds again next spring. They will be looking for mates (and nesting sites) to start the process all over again.