Wednesday, June 1, 2016

Some Confusing Plumages for Some Common Birds

In my column last week I mentioned my birding group at Pee Dee National Wildlife Refuge enjoyed views of a first-year male orchard oriole. I received several inquiries as to how I knew how old the bird was. Many sandpipers have distinctive juvenile plumages that the birds hold through the fall migration. Gulls can take from two to four years to reach maturity and may have a distinctive plumage for each year of their immaturity. Each spring, area birders see some summer tanagers that are in the process of molting into adult male breeding plumage from immature plumage, but those birds are rapidly coming into the adult plumage.

The orchard oriole is somewhat unique among our common breeding birds in that it has a first-year male plumage that is very different from the adult plumage. The young birds arrive in the spring along with mature adult males, sing the same song, and establish territories. But where two year-old males and older have a familiar oriole pattern of black and chestnut the younger birds are lemon yellow with a prominent black bib. It can be extremely confusing to an inexperienced birder. It looks like a completely different species, and though most field guides depict the younger male plumage it is often overlooked when thumbing through identification references. 

Though the younger birds are able to reproduce they have difficulty in finding a mate because females usually will pick an adult male to maximize nesting success.

Another songbird that causes similar confusion is the American redstart. Like the orchard oriole, the one year-old males do not attain the black and orange plumage of adults until they are two years old. These males closely resemble females and will sing the American redstart song during migration and through the breeding season, but also are less unsuccessful at breeding for the same reasons as the orchard oriole. 

For both species, it may be a strategy to enable females to readily identify the younger, inexperienced males in order to pick a male that is better able to select and defend a territory; and help with parenting duties. 

First Year Male Orchard Oriole by Lee Weber

Two + Year Old Male Orchard Oriole by John Ennis

First Year Male-plumaged American Redstart by Jeff Lewis

Two+ Year Old Male American Redstart by John Ennis

1 comments: reviews said...

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