The Curve-Billed Thrasher

Toxostoma curvirostre

Curve-billed thrasher perched at the top of a honey mesquite shrub.

The curve-billed thrasher, which forages on the ground beneath shrubs and cacti, is about a foot in length and generally grayish brown in color. It has robust legs, feet and bill - typical of ground-foraging birds - which it uses to shuffle through plant litter and dig into the soil in its search for seeds and insects. During the breeding season, the male may take a conspicuous perch and issue a loud and melodic call for a mate. The male and female resemble each other closely. The bird may belong to any one of several subspecies, some of them confusingly similar, across its expansive range.

Distinctive Features

Approx. one foot in length
Wingspan approx. 13 inches
Color is grayish-buff
Throat may be whitish
Bill and legs black in color
Downward curved (“decurved”) bill.
Eyes are orange in color
Long tail feathers

Range and Migration Habits

The curve-billed thrasher occupies a wide range. In the United States, the bird occurs most commonly in the western two thirds of Texas and in the southern halves of New Mexico and Arizona. In Mexico, it occurs from the states of Sonora and Chihuahua southward to Oaxaca, south of Mexico City. It inhabits lower elevations from the Sea of Cortez eastward to the Gulf of Mexico. Some populations in the northern parts of the bird’s range may migrate over limited distances, moving, for instance, from mountain flanks down into desert basins during the winter and returning from the basins to the mountain flanks in the summer. Other populations appear to remain in the same area year round.

Habitat

In the desert basins of Arizona, New Mexico and western Texas, the curve-billed thrasher prefers shrub and grasslands that have cholla cacti, a choice plant for nesting. Along the mountain flanks, it favors thorny thickets at the edges of pinon pine and Gambel oak woodlands. In its scrubby and prickly home, the bird moves in quick, darting runs or flys from bush to bush.

Diet

The curve-billed thrasher’s diet includes:

Seeds
Cacti fruit & berries
Insects

Using its curved bill as the primary instrument for sorting, nervously and quickly, through plant litter and for digging in the soil, the bird seeks out cacti and other plant seeds as well as various insect prey. In season, it feeds on cacti fruit, which offers both nutrients and moisture during the months of drought. It may visit backyard seed feeders placed on the ground or hung from lower branches.

Behavior/Life Cycle

A curve-billed thrasher, with its mate, may proclaim territory by singing from perches at the perimeter, which can encompass several acres. A pair may occupy the same territory throughout their lives.

They will defend their immediate nesting neighborhood and food sources vigorously against competitors from other species as well as those from its own species.

Typically, a pair, which may form a long-lasting bond, mates in the winter, after a courtship laced with song. Beginning in the early spring the two birds cooperate in building a nest, fashioning a bowl-shaped structure lined with long grass, ideally in the lower, more shaded branches of a cholla. (By contrast, the cactus wren often builds a rugby ball-shaped pouch-like nest in cholla.) The female curve bill thrasher lays her bluish green to yellowish blue eggs with reddish brown speckles early in the morning on successive days, usually producing a total of three or four. Both birds incubate the eggs.

Within some two weeks, the pair watch as their offspring begin to hatch, naked and helpless, on successive days, in the order in which the mother bird laid the eggs. Over the next two to three weeks, the pair struggles to tend to their nestlings. They answer their nestlings’ incessant cries for food, which may include fruit, pollen, nectar and insects taken from nearby cacti. They fret over their nestlings’ squirms as limbs develop and feathers appear. They oversee their nestlings’ emergence from the nest and their first clumsy attempts at flight.

For the next several weeks, they nurture the fledglings, still answering their cries for food but teaching them the art of foraging and reinforcing their call to independence. About six weeks after the female produced her first clutch, her offspring will take their leave, looking forward, with good luck, to a lifespan of several years. Meanwhile, the female rushes to produce a second clutch, and maybe even a third, before the season ends.

Life’s Hazards & Predators

Typical of nature, a young curve-billed thrasher faces an obstacle course of life-threatening hazards as it grows and matures. In hard times, it may simply starve, its parents unable to provide sufficient food. It may fall to predation by a snake, a raptor, a roadrunner, a rodent, or, occasionally, ants. It may even impale itself, inadvertently and fatally, on a cactus thorn.

Interesting Facts

A pair of curve-billed thrashers may build successive nests in the same cholla, sometimes superimposed over cactus wren nests.
Once they leave the nest, young curve-billed thrashers may “play,” bouncing, hopping and circling, using their beaks to tug at grass and twigs.
When courting a potential mate, the curve-billed thrasher produces a surprisingly lyrical song, with great variation in its phrases, according to the famed naturalist Roger Tory Peterson in his Western Birds.

by Jay Sharp

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