The color of the iris of some birds changes with age, especially in the raptors. The juvenile Red-shouldered Hawk, Buteo lineatus, has a medium brown iris, which will darken with age. The keen vision of hawks, and in fact of many birds, results in part from their large eyes in relation to their head size, as well as the anatomic structure of the eye itself. The Birder's Handbook (Ehrlich,Dobkin,Wheye) has a great essay, "Hawk-eyed" p. 229-231, that explains some of the structural features of a hawk's eye that gives it a visual acuity that far exceed the sharp vision of a human. Too much to relate here, plus you should all have this book on your shelf, as it is a most readable and interesting source that goes far beyond what you'll find in a bird guide book.l I know, most already have the book, but like me you probably don't refer to it often enough!
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| Juvenile Red-shouldered Hawk on Bush Lupine, Pierce Pt. Road - Point Reyes National Seashore
Closer view show the color of the iris better: Juvenile birds have streaky chests, whereas our western adult Red-shouldered Hawks are a rich orange.
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Closer still:
This young bird was oblivious to our presence, and in fact seemed to follow us along the path, catching grasshoppers that fled at our approach.
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