From Hatching to Fledging

Joe Meche is a member of the board of directors of the North Cascades Audubon Society and is in his eighth year as editor of the chapter newsletter. Joe is also a member of the board of directors of the Washington Brant Foundation. He has been photographing birds and landscapes for over 30 years and has been watching birds for more than 50 years.

Eggs are among nature’s most intriguing wonders and the place where all birds begin their lives (see “Beaks and Bills,” June 2004). From fertilization to hatching, the eggs and the young birds within are protected and nurtured by the adults. For those that survive the often tenuous incubation period, a new world awaits as they break free of their shells to begin what many consider to be the most difficult period of a bird’s life.

Between hatching and fledging, the young bird is called a nestling. The first order of business, however, is to get out of the egg, in the process known as pipping. Just before pipping, the chick assumes a tuck position inside the egg and breaks into an air chamber, still inside the egg, and begins to use its lungs for the first time. To free itself from the egg the chick uses two fascinating adaptations—the egg tooth and the hatching muscle on the back of its neck.

The pecking power comes from the hatching muscle and the sharp, calcified egg tooth is used to break the shell. Remarkably, both of these adaptations are transient—shortly after hatching, the hatching muscle withers and the egg tooth drops off or is absorbed. Some parent birds, when sensing difficulty, will peck away at the egg to assist in the hatching process.

One of the first duties of the parents after the hatch is completed is to remove the litter of eggshells from the nest to maintain camouflage and reduce the potential for predation. The nest can be quite chaotic when all the chicks have hatched and the demands on the parents reach a fever pitch. These demands are in direct proportion to the type of young in the nest. Altricial young are born blind and helpless and must remain in the nest under the care of the adults, while precocial chicks are capable of leaving the nest almost immediately after hatching.

The first days after hatching are critical since the parents must protect the young and, most importantly, regulate their body heat. This is the brooding phase and usually lasts a week or so. Large broods fare better than smaller ones since there is more potential for the nest mates to keep each other warm as they huddle together. One of the most important parts of early development in birds is the ability to generate metabolic heat and maintain a high and constant body temperature. This enables the chicks to gain some degree of independence, thus allowing the parents to spend more time with the next priority—food.

Food is the primary prerequisite for growth, and growth accounts for a major expenditure of energy in development. In the early stages of development, the diet of most birds focuses on protein. The chicks have a unique ability to store excess energy as fat to compensate for interruptions in food deliveries by the parents. This ability to store fat also provides for reserves in the days after fledging when the young birds begin to learn how to feed themselves.

As the nestlings continue to develop, sibling rivalry is another hurdle that must be faced. With some birds, the rivalry can be particularly ferocious. In a manner that is somewhat akin to humans, larger siblings can bully their smaller nest mates, especially when it comes to food. Siblicide is not uncommon, especially among some of the larger birds, like egrets and some raptors. Parent birds react rather impassively to the nest behavior of their offspring and, in some species, the primary method of brood reduction comes when an older sibling kills a younger one.

Studies indicate that the cries of the nestlings stimulate the parents to provide food. The noisier the nest, the more active the parents become in their pursuit of food to fill the hungry mouths. The gaping mouths of the young birds provide good targets for the adults, and some cavity nestlings have colored markings on their mouths to present an even better opportunity to hit the mark.

There is a great range in the feeding techniques and frequency among species. The feeding frequency increases as the nestlings grow and their appetites increase accordingly. Nestlings require two to three times as much food as the adults during the nesting period. Small birds are fed between four and 12 times per hour; eagles will feed their young four to five times per day; and barn owls ten times a night.

Another important function that the parents provide at the nest is sanitation. Nestlings of passerine species and woodpeckers eliminate their waste in fecal sacs, which the parents pick out of the nest and take away to foil predators, but also primarily to keep the nest clean. I’ve spent quite a bit of time observing numerous nests and watched as the adults delivered food to the nestlings, picked up a couple of fecal sacs and then flew away. As the nestlings continue to develop, these activities are almost constant during the day.

The nestlings exercise as they mature by flapping their wings while gripping the nest to flex and strengthen their feet and legs, and to keep themselves from flapping out prematurely. By the time they fledge and leave the nest, the young birds have mysteriously learned how to fly; perhaps not that well, but well enough to begin the first days of the rest of their lives. Most passerine species will stay with the parents for two to three weeks before setting off on their own. Other species like swans, for instance, might spend a year or two with their parents.

From the first days of hatching, the young birds have been imprinting with their parents. After fledging, the biggest challenge for the young birds comes in learning how to find food for themselves for the first time. The time that they spend with the adults after leaving the nest is a time for mimicking the adults’ techniques and fine-tuning their own. Among the numerous tasks to be learned by the young birds is the need to become vigilant of predators. This is a learned behavior that often comes from group feeding and foraging.

Birds learn to communicate and navigate through a series of familial and social interactions early in their lives. After young birds leave the nest, the long days of late spring and summer become the learning days. By the time fall rolls around, another wave of nestlings has fledged and the young birds have reached the status of juveniles. This new generation can now look forward to spring when they will search for a mate and assume their roles in nature’s amazing cycle of reproduction. §