Most Singers Are Territorial Males

Vocal Learning and Culture Midsummer. Yet the air has a snowy bite. Gusting wind and loose rock underfoot make me stumble. I clutch at my breath. In the thin air, my thighs burn and ache with anaerobic effort. In the high plains to the east of this Colorado mountain, browned prairie grasses have set seed, and fledgling meadowlarks squall openmouthed as they pursue their parents. For prairie plants and animals alike, the summer season of parental provisioning has come. But here on the mountain, spring just began. Snowfields persist in a few spots. Elsewhere, floral profusion. After nine months of snow and ice, light and water raise from the stony ground a great abundance of blooms, each one a defiant reply to winter’s long duress. No plant grows higher than my knees on this tundra.

How Many More Days?

Ten paces carry me past hundreds of these glowing disks. This buckwheat is a giant among the dozens of wildflowers here, reaching ankle height. Miniature avens, asters, waterleafs, and phlox add varied purple hues. Most plants have stems densely matted with silver hair. This felt protects them from wind and ultraviolet light and, along with the darkness of foliage, traps heat, quickening the plants’ inner chemistry in the short growing season. Flowers are heat catchers too, warming their nectar and offering visiting insects sips of sweet alpine hot toddies. This carpet of miniature flowers is interspersed with shrubby alpine and snowy willows. Like the wildflowers, the willows’ stems and leaves are fuzzy. Every plant is festooned with spiky green baubles that enclose the developing seeds. The willows bloomed before their leaves emerged, when snow first started to melt, welcoming on warmer days the year’s first ants, bees, and flies with pollen and nectar. Subalpine fir, a tree that lances twenty or more meters high at lower elevations, maintains an outpost of crouched, windswept trees here. Every individual is pressed to the ground, growing from trunks turned horizontal.

Straight Down The Middle

Branches sprout thickly around these recumbent spines, making each tree a flattened, elongate thicket, impenetrable to human limbs. Thousands of flowers within arm’s reach. Tens of thousands within eyesight. My eyes, used to a world on a larger scale, implore me to lie down, to get close and imbibe. Prostration is impossible without crushing the delicate blooms or impaling myself on a jagged stone, and so I hunker down on the worn mountain trail, dizzy from oxygen starvation and the floral marvels of tundra springtime. We call this place tree line, a boundary, but there is no sharp edge, only a carpeted mosaic of species that thrive where woody vegetation meets its limits. A few plants extend their populations higher, close to the summit, but most dwell in a band where clumps of fir and willow blend with open tundra. Ascending the mountain, it takes an hour, at most, to walk through this world. But this narrow elevational range belies the magnitude of the habitat. Plants here live all along the high Rocky Mountains, then across the vast treeless tundra of the Northern Hemisphere. Moss campion, for example, here confined to a small section of the trail, lives in the mountain ranges of North America, Europe, and Asia, and is common on the open tundra that circles the Arctic. Wind is the dominant sound here, either its hiss and slap as it scours past my ears or in the roar of fir, spruce, and limber pine that carries up from lower elevations.

Alone Again Or?

Into these relatively simple sounds, from atop one of the ragged fir flags, comes a more ornate melody. A steady introductory note, a higher buzz, a trill, then three downsweeps, the whole phrase unfolding in just two seconds. The song repeats, then another voice answers from a willow shrub twenty meters away, and a third from a fir thicket downslope. The songs are complex but not jumbled. The purity of tone and finely wrought structure are full of light and delicacy. Two long, sliding strokes, a rise into a spin and twirl, and quick foot sweeps on landing. A striking contrast to the disordered wind. These birds spend most of the year in their wintering grounds at lower elevations in the mountains and, for some, in the open scrubby vegetation south of here in New Mexico and Texas. Even at the edge of my eyes’ resolution, gazing across a hundred meters of tundra, I see the banded heads as they bob and fly. This seems an extreme environment for a songbird, but from their perspective this mountain slope combines many advantages. The brief summer brings a surge of insect food with little competition. The wildflowers and grasses will shortly offer abundant seed, enough to draw forest birds like siskins and juncos from the lower elevations to the summer feast. Moisture is easy to find in the rivulets that run down from melting snow, a rare luxury in this arid continental interior. And although they are conspicuous when they sing from their elevated perches, at the first sign of danger from hunting goshawks they can drop into vegetation as dense as the thickest lowland briar patch, vegetation that also protects nests from the eyes of ravens. In the breeding season, most singers are territorial males, and some females also sing to defend their food patches or to drive away rivals. From my seat on the stony trail, I listen to the birds and am struck by how each song has its own pitch and structure. Individuality is immediately apparent. This pure, steady introduction flips into a buzzy sound at about the same frequency, then a metallic trill. Three notes at the end dart down from five to three kilohertz. The singer on the willow starts much lower, three kilohertz, and so is recognizable from the first moment of song. The song’s buzz jumps up in frequency, then moves directly to two sweeps, omitting the trill. From the downslope fir, the third bird gives another arrangement, starting between the others, three and a half kilohertz, then a higher buzz, a hard chip note, a trill, and five sweeps.