Scientists estimate there are between 9,000 and 10,000 species of birds on the planet. While this certainly isn’t a shabby number by any standard, updated taxonomic classification systems and calls for researchers to study hidden diversity among birds suggest that the number of actual bird species might be closer to a staggering 18,000. Yet for all this vast diversity, these avian cousins share one thing in common: the bird life cycle.
TL;DR (Too Long; Didn't Read)
Hatchlings crack open their eggs and become down-covered nestlings who rely on their parents for protection and food. Once they begin to feather, juvenile birds are called fledglings and spend their time building their muscles and growing flight feathers. Soon, fully mature birds fly from the nest to find a mate and begin the cycle all over again.
All From an Egg
What comes first, a bird or an egg? While it is impossible to answer this conundrum, it’s certain that all birds begin their lives carefully enclosed in eggs. The size and color of eggs and the amount of time a bird remains inside the egg varies by species, but eventually, all birds emerge from the egg. Some birds possess a specialized, temporary bony growth on their beaks called an egg tooth that helps them crack open the shell. During the time immediately following a juvenile bird’s exit from the egg, it is known as a hatchling.
Inside the Nest
Juvenile birds are covered in soft down instead of feathers and cannot fly. This makes them vulnerable to predators and incapable of feeding themselves. At this stage, baby birds are called nestlings because they spend all their time snug in the nest, relying on their parents for protection and food.
Learning to Fly
Eventually, nestlings lose their down and sprout feathers, which they need for flight. Juvenile birds who are growing flight feathers and learning to fly are called fledglings. These young birds work hard to practice the skills required for flying and strengthen their muscles. Once their flight feathers have grown in, fledglings take their first flight, which is called a fledge.
Starting the Cycle Over
Birds that are fully feathered and fly from the nest are now mature birds. These birds are ready to find mates and build nests of their own so they can lay eggs and become parents themselves, thus starting the bird life cycle all over.
There is no right answer to the question of whether the bird or the egg comes first since the life cycle of a bird is a circle with no beginning or end. None of that matters to the impressive number of birds on the planet who spend their lives naturally moving through their life cycle.