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.

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, that has twenty-one members placed in three genera, and one of seventeen global species of the Polioptila Genus. They are known in Mexico as perlite gorrinegra and perlite sinaloense.

They are small in stature. The sexes are different with the females being an overall plain slate-gray with their head being has a pale eye-ring and is slightly darker than the back with the remiges being a paler and browner dusky color of the remiges. The males are of a similar color as the females, but they have a very extensive glossy black cap that reaches well below the eyes and reaching the nape and their eye-ring is diminished being only prominent under the eyes. 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 in color with the outer two rectrices being mostly white. Their bills are long narrowing to a fine, slightly hooked tip with the mandible and tip being blackish-gray and the lower mandible medium gray and their iris is brown. The females are an overall plain slate-gray with the head being slightly darker than back with the remiges being a paler and browner dusky color of the remiges.

The Black-capped Gnatcatcher is found in mesquite thickets associated within arid riparian woodlands and in thorn-scrub and arid deciduous forest at elevations below 500 m (1,650 feet). They consume sessile arthropods. Their nests are subject to parasitism by the Brown-headed Cowbird, Molothrus ater. The young are feed by both parents. The Black-capped Gnatcatcher has been poorly studied and very limited information about their behavioral patterns and biology has been documented.

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

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.

From a conservation perspective the Black-capped Gnatcatcher is currently considered to be of Least Concern with stable, widely distributed populations. Their long-term viability is threatened by agricultural development and cattle grazing of their habitat.