Did you know: What is the developmental timeline from egg to fledge?

As we watch the rookery on the golf course and also see those Eastern Bluebirds growing on the bluebird trail, we note these birds “grow up” at different rates.

The time spent from egg production to fledgling varies by species.  Smaller birds often mature more quickly and may go from newly-hatched chicks to fledgling juveniles venturing out on their own in a couple of weeks or less.  Raptors or larger species, however, may stay in the nest under their parents’ care for several months.  Some examples:

SpeciesIncubationLeave nest or BranchingHatch to Fledge
Ruby-throated Hummingbird11 -16 daysN/A20 – 22 days
Eastern Bluebird12 – 14 daysN/A17 – 18 days
Green Heron19-21 daysN/A16 – 18 days
Laughing Gull22-27 daysFew days after hatching35 days
Great Egret23-26 days3 weeks6 – 7 weeks
Wilson Plover23 – 25 daysShortly after hatching21 days
Brown Pelican29 – 35 daysN/A77 – 84 days
Bald Eagle34 – 36 days9 – 10 weeks56 – 98 days
* N/A means the species goes directly from hatchling to fledgling

Sexual maturity can take even longer, with small birds ready to take their first mates in a year.

A baby Eastern Bluebird will weigh slightly more than its parents when it fledges at just 17 – 18 days.  As seen above, the eaglet takes longer to fledge but it will be nearly full grown at 9 weeks of age. They will add some weight as they develop their flight muscles after they leave the nest. Their wingspan will be as large or slightly larger than the adults at this time.

When a young eagle first leaves the nest, its wing and tail feathers are longer than those of an adult.  As an eagle matures, its wing and tail feathers become shorter and narrower with each successive molt.  The larger wings of a juvenile make it easier for the bird to catch an updraft or weak thermal and to fly slower and in tighter circles than an adult.  The down side of the larger wings and tail is that the juvenile rises slower, sinks faster, and cannot soar as far as the adult.  Adult Bald Eagles are able to flap their wings faster and fly at a greater speed than immature eagles, making them more efficient at chasing down live prey.

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