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Bullock’s Orioles have a black throat and a narrow black line through the eye.  Notice that this species has only one large white wingbar.  Wikimedia Commons photo

Northern Oriole

It is said that

“Whatever happened to the Northern Oriole?” the lady asked me.  “It is right here on page 304 of my bird book, but I can’t find it in your bird guide.”  I asked in what year was her guide published.  Looking in the front of the book, she replied “1983.” 

“Ah, that explains it” I said.  “My book was published in 1999.  The Northern Oriole only existed from 1983 to 1998.”

Of course, that doesn’t really explain how a bird can come and go in the bird books, does it?  No, the Northern Oriole didn’t become extinct.  It was the victim of “splitters.”

 Splitters are ornithologists who find evidence that a particular species of bird should rightfully be split into two separate species.  That was what happened to the Northern Oriole in 1998.  It was split into the Baltimore Oriole and the Bullock’s Oriole.  The other name was officially discarded.

Baltimore Orioles breed in the open, deciduous woodlands common to the northeast.  They arrive on their breeding grounds around the 10th of May and immediately start to sing their lovely whistled song.  Soon, they begin to build remarkable hanging, pouch-like nests.  Usually the female alone makes the nest which she does by pushing plant fibers through a network of woven strands.  Her slender pointed beak goes through rather like a sewing machine making a stitch.  When she pulls her beak back out she grabs a different fiber, thus interlocking the strands.  Over and over she does this.  Finally, when the nest resembles an elongated wad, she gets in and pushes and shoves until a pocket is formed.  Although well hidden in large trees like American elms, the durable nests can be seen when the trees have lost their leaves in the fall.

The Baltimore Oriole's head is completely black and he has two wingbars.  The front bar is orange and the back one is narrow and white.  Wikimedia Commons photo.

Bullock’s Orioles, on the other hand, live in much more arid environments.  They are common breeders in the western half of the U.S., including South Texas.   Bullock’s Orioles seek out mature mesquites for their nest sites.  And in Bee County they often choose mature live oaks.  Their rather unmusical song sounds something like “Chop, chop, chop. Eee-ee-bird.”  The male Bullock’s helps the female build the nest.  In one account, the male was on the outside of the developing pouch and the female on the inside.  He would poke his bill through the wall and hand a fiber to the female who would in turn push it back through in a different location.  The result was a rather beautiful, smoothly-woven, pendant nest.

It seems like these two orioles were different enough to be two species, doesn’t it?  They don’t look much alike.   So, what had happened in 1983 to have combined them into the new species, the Northern Oriole?

 Evidence had been accumulating for years that where the two orioles had an overlap in range, i.e. where east meets west, they would interbreed and successfully raise hybrid young.  This suggested that the two species were not true species, but simply races of the same species.  The “lumpers”, another camp of ornithologists, argued that the two orioles should be lumped together as a single species.  The Northern Oriole was born!

Perhaps because of this lumping, birdwatchers began to really take good looks at the Northern Oriole and its two subspecies.  Scientists did further research.  Geneticists studied their DNA.  Field biologists noted that yes, the two subspecies did interbreed in a few localities in Oklahoma and Kansas, but this hybridization was not widespread.  Plus, Baltimore and Bullock’s Orioles are really very different in plumage, song, and habitat.  The hybridization came to be viewed more as a fluke.  The reproductive isolating mechanisms (behaviors, songs, and choice of habitat that kept the two orioles from interbreeding) were breaking down in only a few rare instances.

The final piece of evidence came in 1995.  A study of the DNA of the whole blackbird family showed that Bullock’s and Baltimore Orioles were not closely related after all!  The splitters convinced the members of the American Ornithologists’ Union to officially divide the Northern Oriole back into two individual species.  When The A. O. U. Check-list of North American Birds, seventh edition, came out in 1998 we again had Baltimore Orioles and Bullock’s Orioles.

Did you notice that I said blackbird family?  Yes, orioles are really blackbirds that happen to have colors other than black in their plumages.  If you could dress a plain blackbird, or a grackle, in a tiny orange muscle shirt, he would resemble an oriole! 

Like blackbirds, orioles do sometimes sample fruit.   This can get them on the wrong side of a farmer or orchard manager.  But studies show that only 21% of the diet is vegetable matter.  The rest is insects, and a lot of the insects consumed are true pests.  The orioles feast on webworms, grasshoppers, boll-weevils, and stink-bugs, to name a few.  As one writer puts it “only a short-sighted churl or ignorant fool would begrudge (an oriole) the few green peas or berries it may help itself to while in season. It fully earns all it takes… by the immense amount of good it does in the destruction of noxious insects.”

The orioles’ penchant for fruit has given birdwatchers the idea of feeding them.   You can mount half an orange on a platform, or use a nectar feeder.  The nectar is the same as hummingbird juice (one part sugar to four parts water), but the holes in the feeder are larger to accommodate the larger bills of orioles.  It is fun to watch the Bullock’s Orioles sip nectar and realize that for 15 years they were only a subspecies!

The eighth edition of the A.O.U. Check-list is due out in 2013.  I wonder what surprises the lumpers and splitters will have for us this time?