Vesper Sparrow, Pooecetes gramineus

Vesper Sparrow, Pooecetes gramineus affinis. Photographs taken within a residential community in Hereford, Arizona, March 2012. Photograph and identification courtesy of Bob Behrstock, Sierra Vista, Arizona (naturewideimages.com).

The Vesper Sparrow, Pooecetes gramineus affinis, is one of three subspecies of Vesper Sparrow, two of which are found in Mexico. They are a member of the Passerellidae Family of New World Sparrows, which has one hundred thirty-two members placed in thirty genera, and the sole global species of the Pooecete Genus. They are also known as the Grass Finch and the Bay-winged Bunting, the Grass Finch and the Hesperian Bird and in Mexico as chingolo coliblanco and gorrrión cola blanca. They are named for their evening song.

The Vesper Sparrow is medium-large in stature and known as a songbird. Males and female similar in appearance with consistent year round plumage, with the males being slightly larger than the females. They are a pale grayish-brown and white below and the upperparts and underparts streaked with blackish brown. They have a narrow whitish eye-ring, pale-centered ear coverts with a dark border, white outer tail feathers and streaks over and behind the eyes. They have a small conical bill, long pointed wings and a long tail. Their bills are pinkish transitioning to brownish on the upper portion of the upper mandible and tip, their iris is brown or dark reddish brown, and their legs and feet are pinkish.

The Vesper Sparrow is a ground-dweller found in dry grass fields, with some shrubs or similar structure and in open habitats including fields, grasslands and cultivated crop fields normally at elevations between 1,500 m (4,900 feet) and 1,700 m (5,600 feet). They primarily consume invertebrates, beetles, caterpillars, grains, grasshoppers, insects, and spiders and some seeds on a seasonal basis. They have life spans of up to seven years. The Vesper Sparrow is poorly studied and very little about their biology and behavior patterns has been documented.

The Vesper Sparrow is easily confused with the Savannah Sparrow, Passerculus sandwichensis and the Song Sparrow, Melospiza melodia (both lack a white-eye ring, white border along the ear coverts and white outer rectrices.

The Vesper Sparrow is a wintertime visitor to Mexico and found in Baja California and south to Oaxaca and Tamaulipas but are absent from the Pacific coast south of Jalisco. The affinis subspecies is found in Baja California, northern Sonora and northwestern Chihuahua. They are partial migrants with the northern subspecies moving to southern locations for wintering and the southern subspecies being year-round residents.

From a conservation perspective the Vesper Sparrow is currently considered to be of Least Concern, however, their populations are believed to be in decline which is attributed to changes in farming practices that have destroyed their nesting habitats and introduced pesticides into their environments.