Black-capped Gnatcatcher, Polioptila nigriceps

Black-capped Gnatcatcher, Polioptila nigriceps restricta. Photograph taken within a residential community in Alamos, Sonora, March 2019. Photograph and identification courtesy of David F Smith, Alamos, Sonora.

Background and Identification

The Black-capped Gnatcatcher, Polioptila nigriceps restricta, is one of two subspecies of Black-capped Gnatcatcher, both of which are found in Mexico. They are a member of the Polioptilidae Family of Gnatcatchers, which has twenty-one members placed in three genera, and one of seventeen global species of the Polioptila Genus. Their nests are subject to parasitism by the Brown-headed Cowbird, Molothrus ater. The young are fed by both parents. The Black-capped Gnatcatcher has been poorly studied and very limited information about their behavioral patterns and biology has been documented. They are known in Mexico as Perlite Gorrinegra and Perlite Sinaloense.

Black-capped Gnatcatchers are small in stature. They are 10 cm (3.9 inches) to 12 cm (4.7 inches) in length and weigh 5 g (0.18 oz) to 8 g (0.28 oz). The sexes are different in appearance, called sexual dimorphism. Females are overall plain slate-gray with a pale eye-ring and tail slightly darker than their back. Remiges are pale brown and dusky colored. The males are similarly colored, but they have a very extensive glossy black cap that reaches well below the eyes. Males also have a thinner eye ring. The side of their head, throat, and underparts are white. Their wings are dusky brown, the greater wing coverts are broadly edged in gray and the tail is strongly graduated and black with the outer two rectrices being mostly white. Both sexes have long bills that narrow to a thin, slightly hooked tip. Irises are brown in both sexes. The easiest way to tell males and females apart is to look at their heads. Males will have a black-capped head, whereas the head of females is light grey. The song of the Black-capped Gnatcatcher is a series of high-pitched, squeaky notes that can be heard during the breeding season.

Habitat and Geographical Range

The Black-capped Gnatcatcher is found in mesquite thickets associated with arid riparian woodlands and in thorn-scrub and arid deciduous forests at elevations below 500 m (1,650 feet). They are often found in areas with dense, shrubby vegetation where they can hunt for insects and spiders.

The Black-capped Gnatcatcher is endemic to northwest Mexico with a few strays found in southeast Arizona. They are found within the lowlands of Western Mexico from eastern Sonora south to Colima. The restricta subspecies is found from eastern Sonora and Chihuahua to northern Sinaloa. Their northern populations are known to migrate southward after breeding.

Common Misidentifications

The Black-capped Gnatcatcher is a straightforward identification that is not easily confused with any other species.

Conservation Status

From a conservation perspective the Black-capped Gnatcatcher is currently considered to be of Least Concern with stable, widely distributed populations. However, the species is considered uncommon and local in parts of its range, particularly at the northern edges. Their long-term viability is threatened by agricultural development and cattle grazing of their habitat.