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8/24/2005

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The Red Oriole

The photo below is in fact a Baltimore Oriole and not some strange hybrid! The unusual red colouration of the bird is likely caused by diet. The phenomenon is commonly found in young Cedar Waxwings whose tail bands can be orange in some parts of the species range. Interestingly, orange coloured terminal bands were not documented prior to the 1950's. The appearance of the colour change coincided with the species population doubling from 1965-1979. So what would cause this?

Honeysuckle is an introduced shrub which produces red berries in mid-summer that many songbird species feed on. During the 1960's the shrubs were endorsed by the U.S. government as a valuable means of improving wildlife habitat. The distribution of honeysuckle increased dramatically during that time and the plants have since spread across the northeast. The increase in numbers of fruit-bearing ornamental shrubs has been credited with the increase in Cedar Waxwing numbers.

The relationship between honeysuckle and plumage variation in songbirds lies in the chemical composition of the fruit. Berries of some Honeysuckle species contain a red pigment called rhodaxanthin which causes the moulting tail feathers of 1st year Waxwings to be orange. Tartarian Honeysuckle was not tested but the species is closely related to Morrow's Honeysuckle (Lonicera Morrowi) which tested positive for the pigment. Tartarian Honeysuckle (Lonicera Tatarica) are abundant at TTPBRS and 2005 was a bumper year for the berry crop. Waxwings, Orioles and Robins were all observed gorging on berries during the first few weeks of August. At least two species of honeysuckle occur at the research station and the presence of Tartarian is known, the other has not been identified. Orange tail bands of young Waxwings have been commonly noted over the past three years of banding at Tommy Thompson Park.

Unfortunately I couldn't find any reference to plumage variance in Baltimore Oriole that is attributable to a diet of Honeysuckle berries. We can only speculate about the cause of the red plumage but diet is certainly plausible. At least 3 young Orioles banded this fall have shown varying degrees of red pigment to the feathers. One pair of Orioles (male and female were banded) successfully reared young on peninsula D in a Cottonwood directly above the shrubs. Certainly these berries would have been a substantial portion of the food brought to the nest by the adults. As the nestlings matured the incoming feathers could have come in red instead of the usual orange or yellow.

If anyone has any comments on this topic or other reports of "red" Baltimore Orioles, please email me!

Dan Derbyshire