Orioles on the life list

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(HOST) When the Ivory Billed Woodpecker, long thought to be extinct, reappeared recently, it made headlines around the world. Today, commentator Ted Levin tells of another species that disappeared and then made a comeback – in less dramatic fashion.

(LEVIN) I heard a Baltimore oriole yesterday. A series of clear, sweet notes delivered from a maple along my running route. Since both sexes sing, a rare quality among songbirds, I’m not sure who I heard. The oriole perched high, and I was plugging along so I couldn’t see whether it was black and orange, the male, or brown and yellowish, the female.

I’m surprised the female oriole has any time for song. Her sack nest – the finest, most complicated bird nest in Vermont – requirers considerable skill and plenty of time to build. The process is random and disorangized and begins with a few strands of grape bark or the inner-lining of milkweed stems draped over the sides of a thin branch. When enough strands dangle – you’d have to be an oriole to make the call – she starts to weave and tie loose ends. Then, she threads plant fibers around the nest the way a kid makes a potholder; each piece goes in and out, over and under. The process takes about three or four days, and all the while, the male stands around and whistles.

The American Ornithological Union (AOU), the preeminent scien- tific bird organization of North America – if not the world – publishes the periodic and authoritative “Checklist of North American Birds”, which names every species found on the continent in taxonomic order, from most primitive – loons – to most recent – songbirds.

The list is not inert. From time to time, one species may be lumped in with another or split apart into one or more separate species. Revisions are research driven, a constant in the ever- changing world of ornithology. I anxiously await each new edition of the Checklist. It is the only time I can add (or lose) a bird to my life list while sitting home in an easy chair.

In 1973, the AOU Checklist of North American Birds combined the Baltimore oriole and the Bullock’s oriole into one species called the “Northern oriole”. Researchers had determined that the birds successfully interbred in a zone of overlapping range on the Great Plains. And my life list grew shorter by one.

Originally, the Plains had been a treeless barrier separating the two orioles; Bullock’s to the west, Baltimore to the east. After the Indian wars of the 1870s, ranchers and farmers balkanized the grasslands and imported shade trees – elms, cottonwoods, Lombardy poplars – to cool their homes and line their streets. Nurtured, the trees survived. Because both orioles depend on droopy-branched trees to glean caterpillars and to hang their famous nests, each bird began to expand its respective range. Where they met, they hybridized.

Then, in the 1995 edition of the Checklist, the AOU determined, after years of field work and DNA testing, that the two orioles did not interbreed as much as had been previously thought and that they were not even each others’ closest relative. The Baltimore oriole is more closely related to the black-headed oriole of Mexico. Consequently, the northern oriole was split back into Baltimore and Bullock’s. Two good species again.

And once again, my life list expanded.

This is Ted Levin of Coyote Hollow in Thetford Ctr.

Ted Levin is a writer and photographer and winner of the 2004 Burroughs Medal for Nature Writing. He spoke from our studio in Norwich.

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