The Life Cycle Of A Bird
Once a baby bird has hatched it goes through a number of stages before it reaches full maturity and understanding the life cycle of a bird can help with identification.
Egg – eggs are laid by female birds in clutches ranging in number from just 1 for condors to as many as 17 for the grey partridge. They are incubated by one or both parents for a period of time until the embryo inside has developed into a chick which is ready to hatch. A chick may have to work for hours or even days to break through the shell of its egg. Most birds have a small bump near the tip of their beak called an egg tooth to help them hatch.
Hatchling – a hatchling is a bird that has just hatched and may be almost completely naked apart from some fine down. Its eyes may not open and it is unlikely to be able to care for itself. The term hatchling is usually used to refer to altricial chicks which are undeveloped and unable to move around. They will stay in the nest for some time and will rely on their parents for feeding and to keep them warm. Precocial birds such as ducks and owls are relatively mature when they are born and are sometimes able to feed themselves and leave the nest soon after.
Nestling – nestlings are chicks that are a few days old and are covered in soft down. There may be signs of flight feathers and their eyes may have opened but they will be unable to leave the nest and will still rely on their parents for food and warmth.
Fledgling – chicks that have developed flight feathers and wing muscles are known as fledglings. They will have started to explore outside the nest but will still be under the care of their parents. Fledglings are fairly awkward and only able to fly for short distances but will be active and able to hop about. The length of time it takes for a chick to fledge varies between species. For example it takes 6 months before the chicks of the great frigatebird fledge and their parents feed them for a further 14 months.
Juvenile – a juvenile bird is at the awkward teenage stage of being a bird. Juvenile birds will have left the nest and will be fully independent. They will be in their first plumage and can look similar to adult birds although they may be duller with less defined markings. Out in the field it can be difficult to identify a juvenile bird and for most species of birds the length of time they are a juvenile is very short.
Subadult – subadult birds are young birds that are older than juveniles but have still not developed adult plumage and are not sexually mature. Some birds such as house sparrows will become sexually mature at just a few months whereas larger birds such as golden eagles won’t become sexually mature until they are 4 or 5 years old. The terms immature and subadult are interchangeable by many ornithologists although immature can be used to refer to any bird that isn’t an adult.
Adult – adult birds are sexually mature and are able to reproduce. They will be in full adult plumage which may change depending on the season. Some birds have brighter plumage with clearer markings when in breeding season while in other birds, such as puffins, the shape and colour of their bills may change.