By what developmental stage does the Whooping Crane's iris color settle into the permanent adult shade of yellow?
Answer
By the end of their first year
The coloration of the iris, the structure surrounding the pupil, undergoes a distinct sequence of changes as a Whooping Crane matures from a hatchling to an adult. A newly hatched chick possesses an iris that is blue. As the bird develops through its early chick stage, this blue color gradually shifts and transitions to gray. The final transformation to the established adult coloration occurs by the conclusion of the first year of life, at which point the iris becomes permanently yellow. This sequence—blue to gray to yellow—provides a reliable indicator of age progression during the first year, before the bird achieves its full adult plumage late in the subsequent second summer.
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