Orioles Double Stuff

By Jim Pauff

Orchard Orioles (Icterus spurius) look like Baltimores dipped in mahogany wood stain which shrank them when it dried.  At six inches long, orchards are North America’s smallest blackbird.  There are more around than is obvious.  They breed not only in the United States and Canada but as far south as Baja California and northern Mexico.  All orioles spend winter in the tropics or neo-tropics where, like true blackbirds, they flock in small, noisy, chattering, scolding groups.  At night, flocks sleep in tall dense grasses—like Red-winged Blackbirds among cattails in North America.

Orchard Orioles are studied in countries like Panama because they fertilize a large forest tree (Erythrina fusca Loureiro) by sipping nectar from its flowers.  Only Orchard Orioles do this; other wintering orioles peck through the base of the blooms to steal nectar.  The flower has some mahogany color and scientists wonder if that causes the difference in behavior.  Coming north, Orchards will steal nectar from trumpet creepers in the same way their relatives do down South, pecking through the flower bottom.

In the 1970s ornithologists concluded Baltimore Orioles and Bullock’s Orioles were the same bird, and called both “Northern Orioles.”  Why they did this seemingly defies logic, but in any event the brain of bird science reversed itself, going back to the original species designations.  By contrast, Orchard Orioles may soon be divided into two species: our familiar Orchard and Fuertes’ (Icterus fuertesi), which is a lighter-colored Orchard look-alike. Heretofore Fuertes’ was considered only a subspecies.  Now ornithologists refer to both as “the Orchard Oriole group.”  Also called the ochre oriole, Fuertes’ live on the east coast of southern Mexico from Veracruz to Yucatan—the part where Mexico curves around the Gulf.  Fuertes’ don’t migrate far.  Genetic testing and color spectrometry analysis suggest the two are indeed taxonomically separate—but as yet this is not official.  Speculation is some 200,000 years ago Orchards began diverging due to habitat availability.  Those living along the Mexican Caribbean lightened due to terrain differences.  They turned from chestnut brown to gold-ochre.  DNA reveals Fuertes’ do not interbreed with their darker relatives due to geography and separation.  It’s an example of “allopatric speciation”—speciation due to natural partition.

Pigments called carotenoids produce the bright oranges and yellows in oriole feathers.  However, male Orchard Orioles at maturity produce another pigment called phaeomelanin that mutes carotenoids with a reddish-yellow wash.  It isn’t present in females or immatures.  Why melanin masks the flashy colors is a puzzle.  Brightness is often used to claim territory and indicate the health of mates.  These things don’t seem important to Orchard Orioles.  As compensation, perhaps, Orchard Orioles are gregarious.  They will share a large nesting tree near water, close to kingbirds as insurance against predators.  Orchard males give more help to females raising young than larger, brighter Baltimores do.  Orchards also sing a lot.  Speculation is attributes like these make up for losing their flash, being muted but handsome in their own way.