The Secret Life of Mistletoe

THE GOOD, THE BAD, AND THE MISTLETOE

The ancient thick-trunked leafless mesquite held its ground stubbornly on the flanks of the wash bottom, its gnarled upthrust limbs festooned with huge clumps of mistle-toe. The shiny red berries of the encrusting parasite gleamed in the lengthening afternoon light in this landscape of angular rocks and barbed thorns.

Delighted with the discovery of so thick a cluster, I found a bush that could serve as an impromptu blind and settled in the sand for the show. The Druids loved mistletoe, and they cut clumps from the branches of sacred oaks and dispensed them to believers as a spindly, twisted limb of the spirit world. That ancient infusion of reverence led by roundabout symbolism to our own sea-sonal custom of tacking mistletoe over doorways in hopes of cajoling a kiss.

FOCUS ON NATURE

But I watch mistletoe clumps for more secular reasons. They offer a fascinating tutorial in ecology, illustrated with brilliant feathered flashes of blue and black.

At first glance, parasitic mistletoe seems an ugly, dishonorable sneak of a plant. Its tiny seeds sprout a unique shoot that attaches itself to the host plant, infiltrates the bark of its host, and grows into tumorlike tendrils. Once established the mistletoe leeches nourishment for the rest of the infected host's life.

Some 20 species of mistletoe infest all manner of plants, including Arizona varieties that cling to ponderosa pines, oaks, cottonwoods, willows, mesquite, catclaw, creosote, and a number of other woody plants. Sometimes the parasites effectively drain the life from the host, especially if the host plant has an overabundance of mistletoe during periods of drought. More often the parasite clings for decades, contributing to the tree's eventual death by drought, frost, or insects.

So what's to love in a clump of mistletoe? Throughout Southwestern deserts, mistletoe provides a crucial link in a complex food chain.

It's chiefly a matter of timing. Mistletoe berries appear in late fall and flourish through winter, just when most other food sources ebb. Trees drop their leaves, insect larvae slumber, and ants live on their hoarded seeds. That's why many birds forsake northern lands for the year-round cafeteria of the tropics. But the appearance of the energy-rich mistletoe berries sets winter's table for certain species. The year-round bugand fruit-eating mockingbirds change their menu as soon as the berries appear, gleaning up to 95 percent of their food from the mistletoe. They hide among the berries like misers gloating over their gold. But they'll flash out into the sun in an instant to defend their berry territory, driving away whole flocks of other would-be fruit eaters.

Often that includes the phainopeplas, which are so intimately connected to mistletoe that they've developed a unique migratory pattern. Most songbirds winter in the tropics and then head north for the spring buffet. Phainopeplas arrive in fall just before the mistletoe ripens, stake out berry-based territories, rear their young, then head south again in May and June, neatly avoiding the summer heat. It's all choreographed by the mistletoe.

The berries also influence the migrations of other species. Blue-birds, robins, cedar waxwings, sage thrashers, quail, Gila woodpeckers, and other birds rely heavily on mistletoe berries at certain times of the year. For instance bluebirds generally summer at high altitudes then migrate downslope to mistletoe-infested cottonwoods and mesquite. They loll through the otherwise barren winter, relying almost entirely on mistletoe berries.

But it's a fair trade. The mistletoe relies heavily on the birds to spread its seeds. The outer part of the berry sticks to the hungry flyers' beaks, and when a bird cleans its beak on a branch it leaves the seeds behind, possibly giving life to another batch of mistletoe. Some species of mistletoe germinate best after passing through a bird's digestive track, including the desert mistletoe found on mesquite trees in Arizona.Sitting in my clump of bushes, I gleaned considerable pleasure from the thought of this gaudy procession of songsters timing their lives by the clock of the mistletoe. Just then five bluebirds flurried out of the underbrush and alighted on the mistletoe-laden mes-quite branch. They fell to the ber-ries with joyful intensity. But they had barely enough time to smear seeds on their beaks before a furi-ous mockingbird erupted from a nearby mesquite and hurled itself at the intruders. They scattered in a great spatter of blue, unwilling to match their courage with a bird that enjoys taunting hawks. The mock-ingbird perched triumphantly on the mesquite, preening the chip on its shoulder.

I simply watched. He gobbled several berries, then flaunted back to the other mesquite. I disentangled myself from my bush and broke off a mistletoe twig for my wife, like a Druid grasping at some-thing sacred.